The following recommendations allow you to provide reliable power and communication to the SmartSensor HD.

Understanding SmartSensor 8-conductor Cable length limits

The 8-conductor cable has conductors for one power and two communication channels, each with its own requirements and length limitations:

• DC power – These two conductors (red and black) are 20 AWG wires. Based on DC power limitations and the power drawn by the SmartSensor HD, this means that power can travel up to 700 ft. (213.4 m) along these conductors.
• RS-485 communication – This twisted pair (blue and striped blue/white) are 22 AWG wires. Based on RS-485 limitations, and the specifications of the twisted pair, this means that communication can travel up to 1400 ft. (426.7 m) along these conductors.
• RS-232 communication – These four conductors (orange, brown, violet, and yellow) are 22 AWG wires. Based on RS-232 limitations, this means that communication can travel up to 200 ft. (61 m) along these conductors.

Proper sensor functionality requires DC power and one communication channel. Having a second communication channel allows for sensor configuration without detection data interruption.

This document discusses power and communication requirements for SmartSensor HD in more detail and provides recommendations on how to achieve sensor functionality in various applications based on voltage, needed cable length, and desired number of communication channels.

DC Power and the SmartSensor HD

The operating voltage for the SmartSensor HD is 10–28 VDC. The recommended power supply voltage is 12–24 VDC, with a 5% voltage tolerance.

Due to HD power consumption, DC power can only travel a maximum of 700 ft. (213.4 m) along the 8-conductor cable. However, the 8-conductor cable is specified for cable runs up to 1400 ft. (426.7 m), based on RS-485 capability. To extend DC power to 1400 ft. (426.7 m), sacrifice RS-232 conductors in the cable and combine them with the power conductors when terminating the cable into the Click 200.

Extending DC power up to 1200 ft. (365.8 m)

Since the 8-conductor cable’s RS-232 capability is lost after 200 ft. (61 m), those conductors can be easily sacrificed to extend DC power up to 1200 ft. (365.8 m) at 24 VDC.

Follow the steps below to correctly terminate the 8-conductor cable into a Click 200 and achieve a maximum cable length of 1200 ft. (365.8 m) at 24 VDC:

1. Terminate the orange conductor (normally RTS) into the same terminal as the red (+DC) conductor.
2. Terminate the brown conductor (normally CTS) into the same terminal as the black (-DC/GND) conductor. Leave the yellow and violet conductors; they do not need to be connected to anything, in this case.

Note. At 1200 ft. (365.8 m), your cable will only be carrying DC power and RS-485 communication.

Extending DC power up to 1400 ft. (426.7 m)

To reach 1400 ft. (426.7 m) at 24 VDC using the 8-conductor cable, sacrifice two more RS-232 conductors for DC power.

Follow the steps below to correctly terminate the 8-conductor cable into a Click 200:

1. Terminate the orange conductor (normally RTS) and the yellow conductor (normally TD) into the same terminals as the red (+DC) conductor.
2. Terminate the brown conductor (normally CTS) and the violet conductor (normally RD) to the same terminals as the black (-DC/GND) conductor.

Communication and the SmartSensor HD

As mentioned above, while only one communication channel is needed for sensor functionality, a second communication channel allows you to connect to the sensor for configuration without interrupting the data being sent from the sensor.

RS-232

While the 8-conductor cable contains four conductors for RS-232 communication, cable runs over 200 ft. (61 m) will lose RS-232 capability. If you wish to use RS-232 at a distance of more than 200 ft. (61 m) from the sensor, RS-232 must be converted to RS-485.

Note. The SmartSensor 8-conductor Cable is not suitable for this type of conversion; you will need to use the SmartSensor 6-conductor Cable. For detailed information on how to convert RS-232 to RS-485 using a Click 304, see knowledge base article 0532 Using the Click 304, available at www.wavetronix.com.

RS-485

The 8-conductor cable contains a twisted pair for RS-485 communication. Cable runs over 1400 ft. (426.7 m) will begin to lose RS-485 capability.

Recommendations

The following tables give recommendations for various applications based on power, cable length, and number of communication channels. For more information or support, contact your Wavetronix representative.

SmartSensor 8-conductor Cable

The table below shows applications based on power voltage, and the conductors needed to achieve maximum cable length.

‍Note. For RS-232 conversion, or for applications with two RS-485 channels under 700 ft. (213.4 m), we recommend using the SmartSensor 6-conductor Cable.

Using an alternative cable

Below are Wavetronix recommendations for alternative communication cables. If you need an alternative power cable, any 2-conductor copper wire at the proper gauge will achieve the desired result.

Note. For cable runs up to 1400 ft. (426.7 m), we recommend you use a Wavetronix cable; if you choose to use an alternative cable, it must meet or exceed Wavetronix cable specifications. For cable runs longer than 1400 ft. (427 m), ensure the alternative cable used meets specifications for the power and communication standards being used. Failure to do so could cause devices to function improperly.

Communication cables

• Belden 3105A – One twisted pair with 22 AWG conductors used for one RS-485 channel.
• Belden 3107A – Two twisted pairs with 22 AWG conductors used for two RS-485 channels.
• Alpha 6453 – One twisted pair with 22 AWG conductors used for one RS-485 channel.
• Alpha 6455 – Two twisted pairs with 22 AWG conductors used for two RS-485 channels.

Power cables

The table below shows the voltage and wire gauges needed to provide DC power up to 2000 ft. (609.6 m).

Choosing a baud rate for wired communication

To achieve reliable wired communication, the selected baud rate must be compatible with the length of the cable run. The table below shows the cable length recommendations for wired communication.

*This is possible with an alternative cable.

Last updated September, 2010

The SmartSensor HD can be used as an automatic traffic recorder (ATR) in the process of gathering, storing and analyzing traffic data. In this process, the data is first collected by the SmartSensor HD and stored in the sensor’s internal, non-volatile memory. The data is then downloaded and put into an Excel spreadsheet for plotting and further data analysis. The flow of this entire process is shown in the figure below.

Since no communications infrastructure is required in this system, the process described in this article is suitable for use at temporary or permanent sensor stations.

Automatic Traffic Recorders

ATRs are an invaluable tool in the field of transportation planning. Whether used for continuous monitoring at a permanent location or temporary collection via a portable trailer, ATRs provide baseline vehicle data critical to analysis of multi-modal transportation propositions.

Key baseline data for planning analysis includes:

• Traffic counts
• Vehicle classification
• Spot speeds

Traffic count data is necessary for many of the following reasons:

• To appropriate transportation project funding
• To compute accident rates and vehicle miles traveled
• To evaluate air-quality impacts of motor vehicle travel
• To estimate trends to plan for future demand
• To calculate travel times of alternate routes
• To design transportation channels, structures, geometry, and signalization

Spot speeds and vehicle classification of count data are necessary to refine the analysis in several areas, such as structural design of pavements and bridges, congestion impacts on air quality and user costs associated with travel time and fuel consumption.

The accuracy, consistency and reliability of baseline traffic data is crucial because of the long-term impact that transportation planning decisions have on the development of our local, regional and national communities. High-definition ATRs like the SmartSensor HD provide accurate lane counts, reliable vehicle classification and accurate per-vehicle speeds in order to establish a solid baseline for decisions.

The SmartSensor HD can be used as a non-intrusive ATR station with multi-lane and auto-configuration capabilities that provide planning agencies with a unique opportunity to increase the sample size of their baseline data at a reduced cost. In some cases, planning and operations departments can share the same SmartSensor HD ATR station to further increase the cost-benefit ratio to the public.

SmartSensor HD Deployment

The SmartSensor HD with either a permanent or temporary sensor site can be used as an ATR. The top figure below shows the SmartSensor HD in a temporary deployment on a trailer. In this scenario, the sensor is powered by a rechargeable 12 volt lead-acid battery. Since a SmartSensor HD unit consumes less than 9 W in all weather conditions, a 75–100 amp-hour deep-cycle battery should be sufficient for 48-hour studies. The battery will need to be recharged between monitoring periods, or it can be continuously charged using a solar panel system.

The bottom figure shows the SmartSensor HD in a permanent installation. Serial communication to the sensor is available in the pole-mount cabinet shown in the drawing. A Wavetronix preassembled Click cabinet is recommended for this application. The cabinet will provide surge protection, AC to DC power conversion and terminal blocks for cable termination. If a communications infrastructure is available, the Click product line provides a number of communication options for integrating into existing infrastructures.

SmartSensor HD Internal Storage

The SmartSensor HD was designed with features that facilitate onboard data storage and traffic studies. First, the sensor is equipped with a real-time clock powered by super capacitors that will continue providing power even when power is not supplied to the sensor. This clock provides an accurate time base that is used to timestamp the data as it is collected by the sensor.

Second, the sensor was designed with a large amount of internal memory. This memory is non-volatile and thus stored data will not be lost if the sensor loses power. The number of interval data records that can be stored on the sensor varies with both the number of lanes that are configured and the number of classification bins and speed bins that are configured. The table below gives some onboard storage capacity examples:

Third, the SmartSensor HD includes a rich set of interval data. Besides volume counts, average speed and occupancy, the sensor also stores 85th percentile speed, average headway, average gap, counts in up to eight length-based classification bins, counts in up to 15 speed bins and counts by direction of travel (see the Data Storage & Download section and the Bin Definitions section of Chapter 8 in the SmartSensor HD User Guide for details on how to configure the storage of interval data).

Data Download Using SSMHD

Once the sensor has stored the data to be analyzed, the data is downloaded to a text file using SmartSensor Manager HD. This process is described in the Data Storage & Download section in Chapter 8 of the SmartSensor HD User Guide. As shown in the figure below, this text file is user-readable and contains all the interval data that the sensor is configured to store.

Importing Data into Excel Using DataExpress

Wavetronix distributes the software application DataExpress as freeware to aid traffic professionals in importing SmartSensor interval files into Excel. This application allows you to load a text file and select which of the data in the file should be imported into Excel (see the figure below).

Before loading the data into Excel, the intervals can be aggregated into larger intervals. For example, if the original file contained 5-minute intervals, then DataExpress could aggregate the data into 15-minute, 60-minute, 6-hour, 12-hour, 24-hour, 7-day or 1-month intervals. This feature is needed when the text file contains a very large amount of data that would be too cumbersome to work with in Excel. By aggregating the intervals, the amount of data can be reduced before creating an unmanageable Excel file. When using the 2007 version of Excel, DataExpress will also create plots of the volume, speed and occupancy data.

Once the data has been imported into Excel, the traffic professional now has all the data analysis tools of Excel available for viewing and manipulating the data.

SmartSensor HD can be a powerful tool for collecting traffic information, and a properly designed installation site is an essential part of this process. Follow these 10 tips to ensure that you get the best results from your SmartSensor HD installation.

1. Have a plan

Know in advance how many sensors you will need and where to install them. The location of sensor stations will depend on how you plan to use them: if you intend to use the sensors to detect incidents or to generate travel times, you will want to place your sensors as close together as possible; if you plan to only use the sensors for data collection, then they can be placed farther apart.

2. Avoid queuing traffic

SmartSensor HD is designed to detect moving vehicles, so you will want to place your sensor where traffic is flowing. In most highway installations this won’t be a problem, but for mid-block installations, you can run into congestion problems if the sensor is placed too close to an intersection. Make sure you install your sensor as far away as possible from intersections and other sources of congestion.

3. Avoid multipath

Multipath can occur when there are flat structures near the sensor, such as buildings, retaining walls and sound walls. Part of the reflected signal may bounce off these structures, resulting in false vehicle detections. In the top image at the right, part of the radar signal is reflecting off the vehicle and returning directly to the sensor (the black arrow), resulting in an accurate detection; the rest of the signal (the red arrow) is scattered and might cause a phantom detection, as seen in the bottom image. Try to choose mounting locations where there aren’t walls or buildings directly behind or in front of the sensor.

4. Avoid occlusion

SmartSensor HD can only detect what it can see, so if something blocks the sensor’s view of the road, the sensor might miss detections. This is called occlusion. Things that can cause occlusion include trees, tall barriers and signs. Occlusion can also be a problem in areas with high truck traffic because trucks can block the sensor’s view of smaller cars. The best way to avoid occlusion is to install the sensor away from obstacles, but you can also increase the mounting height to allow the sensor to see over the obstacles.

5. Put space between facing sensors

If your SmartSensor HD faces any other radar device, including another SmartSensor HD, the signals may interfere with each other. For optimal performance, your sensor needs to be at least 70 feet up- or downstream from any facing radar device in the vicinity. It is also a good idea to put them on different RF channels; this will lessen the chances of interference.

6. Find a location where lanes are parallel

SmartSensor HD should be placed, as much as possible, perpendicular to the flow of traffic. Normally this is easy to do, but sometimes there will be non-parallel lanes — for example, on- and off-ramps, frontage roads, or non-parallel sides of a divided highway. If you must install in such a location, the sensor’s software allows you to exclude these problem lanes.

7. Plan around existing infrastructure

To avoid unneeded expense, look for spots where poles and power sources are already in place. You can use most poles, as long as they fall within the height and offset requirements. If there’s already electricity in the area for luminaries or electronic signs, tapping into these may be easier than running new power lines out to the mounting location.

8. Keep away from overhead structures

Overhead structures such as overpasses, bridges, tunnels, pedestrian walkways and overhead signs can cause multipathing and other detection problems. Install your SmartSensor HD at least 30 feet up- or downstream from any such structure.

9. Look for even terrain

Sometimes when divided highways run through uneven terrain, one side of the road may be at a higher elevation than the other. Depending on the difference in elevation, this could cause detection problems, as shown in the picture below. Try to avoid installing in areas where the difference in elevation is extreme enough that the sensor isn’t getting a good view of the entire road.

10. Use proper height and offset

SmartSensor HD must be installed at the proper height and offset. Offset refers to the distance that the sensor’s pole is set back from the first lane of interest; if there is a frontage road or ramp that doesn’t need to be detected, it doesn’t matter in determining the offset. SmartSensor HD’s minimum offset is six feet; there is no maximum offset, but you need to make sure that all of the lanes you want to detect fall within the sensor’s 250-foot range. How high you mount the sensor will vary depending on the offset — the important thing to consider is how well the sensor can view all lanes. At least 50 percent of a vehicle must be visible for the sensor to detect it.

The SmartSensor HD gathers accurate detection data from up to 22 lanes of traffic. With its nonintrusive placement and its helpful alignment and configuration software, the SmartSensor HD is quick and easy to install. Following the 10 installation tips below will ensure you get the best possible performance from your sensor.

1. Know your purpose

The SmartSensor HD improves many aspects of traffic management, gathering data for a host of different applications:

• Count stations
• Congestion alerts
• HOT lanes
• Speed maps
• Ramp metering
• Trip times
• Incident management
• Variable speed limits
• Work zone management

How you install the sensor will depend on the applications you’re implementing.

2. Know where your sensor will go

Once you’ve decided the general area your sensor will be installed in, assess the area to see if there’s any existing infrastructure you can take advantage of. Using existing poles and/or power sources for your installation will spare you the expense of putting them there yourself.

Keep in mind that the pole you use must fall within acceptable offset requirements. If no poles fit the requirements, you will need to have one placed on the site.

3. Come prepared

Make sure you have everything you need before you go to the installation site.

• The SmartSensor HD and mount, plus Click equipment and cables
• Bandit clamping system for fastening the mount to the pole
• A basic toolkit, including a screwdriver, multimeter, wire stripper and crescent wrench
• Pertinent documentation
• Draw wire or similar equipment for pulling the cable through conduit
• Multiple ways to connect to the sensor, such as serial cables and a USB to RS-485 converter (it is recommended you come prepared with multiple means)
• Laptop or PDA with SmartSensor Manager HD installed
• Bucket truck

4. Don't worry about lane closures

Many traffic detectors must be placed in or under the asphalt, meaning that installation and maintenance require costly, inefficient and dangerous lane closures. But the SmartSensor HD is an above-ground, nonintrusive detector, so the installation process keeps your traffic flowing and your personnel out of the road.

5. Don't worry about maintenance and adjustments

Once the SmartSensor HD is installed and aligned properly, you’re done! Unlike other traffic detectors, Wavetronix sensors require almost no maintenance: they are unaffected by road damage or resurfacing; they don’t need to be cleaned or tuned; and they last for years.

6. Power your sensor

Along with the sensor itself, you’re going to need a cabinet with the power, surge, and communication devices to support your installation. The SmartSensor HD, and all the devices in the cabinet, run off of 24 VDC power. You have several options for power:

• If there’s already DC power coming into the cabinet, you just need surge devices to make sure that power is clean.
• If there’s AC power coming into the cabinet, you’ll need an AC to DC converter.
• If your installation is remote enough, you may want to consider an alternate power source, such as solar panels.

DID YOU KNOW? Wavetronix offers preassembled cabinet systems ready to power, protect and connect your installation right out of the box. These end-to-end systems simplify the ordering and installation process because they arrive prewired and are tailored to meet your needs.

7. Connect your sensor

You need to decide how you’re going to access the data the sensor is collecting. For a count station or similarly remote installation where you’re going to manually download the data in person, you may need a short-range communication device (e.g. Bluetooth). If you’d like to be able to connect to the sensor from your TOC, however, you’re going to need a communication device in the cabinet that will send your data via a long-distance medium such as Ethernet, fiber or radio.

8. Protect your sensor from surges

It’s important to protect your sensor and your cabinet from surges coming from the power source or any underground cable runs. Use a circuit breaker and a power surge protector in your cabinet to protect it from surges from the power input. If you have an underground cable run—for instance, from the cabinet to a pole-mount box directly beneath the sensor—put a surge protector on either end of the cable run to protect both the cabinet equipment and the sensor from any surges on that cable.

9. Align your sensor

Before you leave the installation site, make sure the sensor is aligned properly. First, point it perpendicular to the flow of traffic and down toward the center of the lanes of interest. Then connect to the sensor with your computer and use the alignment tool found in the SmartSensor Manager HD software to verify that you’ve aimed it correctly.

10. Set up your lanes

The last thing to do in the installation process is to configure your lanes. SmartSensor Manager HD’s user-friendly auto-configuration process will detect passing vehicles and determine where the lanes in the roadway are. Once this is completed, you can use the manual configuration options to make adjustments, if needed.

DID YOU KNOW? The SmartSensor HD collects much more than simple vehicle presence data; its innovative dual-radar design also detects speed, 85th percentile speed, volume, occupancy,  headway, gap, and size classification.

The user-friendly software, SmartSensor Manager HD, allows you to choose whether to collect this data for each vehicle that passes or for set intervals of time.

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Accurate, up-to-date traffic data is a vital part of planning for future roadway demand and for receiving tax revenue funding. But what do you do when you need this data for a roadway where you don’t have any detectors and no plans to install them in the future? Enter the temporary count station.With its quick, non-intrusive setup and accurate data collection, SmartSensor HD is perfect for this application. To use the HD for a count station, follow these easy steps.

1. Choose a mounting location

Count stations can be placed in a variety of locations, both rural and urban. Wherever it is that you need traffic counts, the first thing to consider is what the sensor will be installed on. If there’s an existing pole in the area, then that may be the easiest spot to choose. If there are no suitable poles, consider using a trailer. Some agencies keep trailers with the pole, sensor, and supporting equipment already assembled and ready to go.

2. Consider power

The general location of your sensor will help determine how you power it. If there is already any kind of power infrastructure in the area, consider tapping into that to power your sensor. Whether that power is AC or DC, the Wavetronix Click product line has a number of power converters and surge protectors you can use to make sure that the power going to your sensor is the required 24 VDC and that it is clean.

What if your sensor is in a rural area and there is no such power infrastructure? In that case, you’ll need another power source. Many count stations are battery-powered, but if this station is going to be running longer than a battery can power it, you may consider solar panels or wind turbines, which are two popular options.

3. Consider communication

There are three basic ways that traffic data can be collected from a count station:  

1. If there is any kind of communication infrastructure in the area, you can connect your sensor to it and set it to push data back to your traffic management or operations centre. The sensor pushes data out over a RS-485 line; if you need to send this data via Ethernet, the Wavetronix Click line has a module for that.
2. In areas where there is no such infrastructure, you could set up the count station to communicate wirelessly with your TOC. Cellular modems are a popular solution in this case, or the Wavetronix Click line has a 900 MHz radio module that can communicate with other radios up to 20 miles away.
3. A third alternative is not to push the data back to the TOC at all. Since count stations are usually set up to collect data over a certain time period, and it’s not necessary for the TOC to receive the data as it’s collected, many agencies choose to have the sensor store the collected data in its flash memory. Then, after the collection period has passed, an employee can drive to the count station and download the data.

4. Configure the sensor

Configuring SmartSensor HD to the roadway is quick and easy using the automatic configuration tool; just make sure the sensor is properly aligned, then start auto-configuration.

Finally, set up the data collection according to how you’ve decided to gather data. If the sensor is meant to send the data to the TOC, configure the sensor to push data over the RS-485 port. If you’ve decided to have the sensor store the collected data onboard, make sure the Storage setting is turned on.

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Ramp metering is a tool used by traffic and ITS engineers to manage the flow of vehicles entering controlledaccess highways or freeways. Controlled-access freeways generally consist of high-occupancy roadways, which in turn result in low or variable speeds and contribute to potential merge friction from vehicles entering the freeway. The principle behind ramp metering is to evenly space the merging vehicles by metering them, reducing the likelihood of congestion and accidents on the mainline.

The Wavetronix line of reliable, non-intrusive SmartSensors detect all the parts of the ramp metering system: the mainline flow, presence at the stop bar, and traffic queue on the ramps. There is always a SmartSensor for your application, whether it is system-wide traffic response or fixed-time operation. Although ramp configurations vary, Wavetronix will help you design a ramp metering solution that fits the needs of your application.

Ramp Stop-bar Detection

For stop-bar detection across the country, Wavetronix created the SmartSensor Matrix: a true presence radar vehicle detector with 16 antennas that can detect stopped vehicles in a 90 degree arc that expands out 140 ft. from the sensor.

In a multilane ramp metering configuration, there are two zones for each lane of travel. The first zone is configured before the stop bar. It is triggered when a stopped or slowed vehicle is waiting to enter the freeway. This zone can be as large as needed and must be long enough to work effectively as a presence detector when there are multiple cars in the queue.

The second zone is not always required, but is useful for systems that use a “passage zone” to ensure the vehicle has left the detection area. This zone signals back to the controller that the car has successfully cleared the area and the green light can be given to the next vehicle, as shown below. Wavetronix SmartSensors can have up to a 0.5-second delay in detecting a vehicle, so the passage zones can be small five-ft. zones. In some situations, it may be easier to make one zone that covers the whole roadway and tie it into the same channels on the controller.

Ramp Queue Detection

For ramp queue detection, the type of sensor you will want to use depends on the type of ramp: straight, clover-leaf, or long.

Straight-approach Ramps

The SmartSensor Advance detects vehicles as they approach the intersection and protects vehicles in the dilemma zone. This detection can happen at multiple zones along the approach, resembling a series of loops along a 600–900 ft. area of detection. There are several ways to detect the level of arriving traffic flow. One way is to monitor queue levels by configuring the SmartSensor Advance to detect the speeds when queue spillback reaches setback locations of interest. This method allows you to continuously activate different channels based on estimated queue length.

A 2009 ramp queue detection report conducted for Mn/DOT by SRF Consulting used four channels to estimate queue length in this way. The study reported that the average error in queue length was 9.2 ft (2.8 m) and the absolute average was 36.1 ft (11 m). These “excellent results” were achieved as the queue length on the ramp fluctuated from 0 to over 250 ft. and back six times during the almost two-hour period from 3:15 to 5:00 p.m.

Note. This feature can also be used in busy off-ramp scenarios where an extension on green at the end of the ramp may be needed to prevent backup onto the controlled-access roadways.

Clover Leaf Approaches or Long Ramps

If detection is needed beyond 500 ft. or the on-ramp is clover-leaf shaped, we suggest using the SmartSensor HD for detection. The SmartSensor HD can detect vehicles traveling perpendicular to the sensor up to 250 ft. away.

In several systems, the occupancy of a particular part of the roadway is used to adjust the signal timing at the stop bar. Sometimes this occupancy is detected by loops or micro loops. The SmartSensor HD can be used to emulate this occupancy detection over a particular space. Using the HD’s loop emulation and corresponding rack cards, the HD will output a call when the space in front of the sensor is occupied. This is especially useful for replacing loops with HDs.

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Picking a mounting location for the SmartSensor HD can be tricky because you almost never have complete control over the environment in your mounting location. You’ll always have to deal with existing obstacles—such as signs, trees, buildings near the road, hills, cliffs, and/or other uneven conditions. So while this document will show you what to look for in a good spot for your installation, the fact of the matter is that it’s usually hard or impossible to find what would be considered an ideal mounting location.

This doesn’t mean, however, that you’re not going to be able to find a good spot where the sensor will work really well. What it really means is that you should approach this document not as a list of things you absolutely must follow when you pick a spot, but more as a list of considerations that you should be thinking about as you choose your mounting location. And make sure you understand which of these considerations are most important—that is, when and how you should compromise. This document will explain which issues are more or less serious, and what problems could arise with each one.

Is this a midblock installation?

SmartSensorHD may be needed in a number of different situations, from a long, open stretch of freeway in the country to a crowded street in the middle of a city. We call this second kind of application a midblock installation (which is a kind of arterial installation), and it poses a particular sort of challenge because of the possibility of obstacles in the area.

One consideration that affects midblock installations is the relative mounting location of the sensor. Surface streets—the streets in the middle of a town or city—are usually dotted with stoplights, which cause traffic near intersections to be in a constant state of change: cars slow down and speed up, queues form and dissipate. For the highest level of accuracy, try to place your sensor in the center of the block, equidistant from the stoplights at either end. This will minimize the amount of time that traffic from either direction is stopped in front of the sensor, leading to a maximum of detection accuracy.

Is there a difference in elevation between the two sides of the road?

This is less common in a very urban location, but can happen in any area: the two sides of a road have differing elevations. The difference may be only a few feet, or it could be quite considerable. How it affects your design depends on how big the difference is:  

• Only a few feet – Sometimes the elevation difference between the two sides of the road is only a few feet, as shown in the image to the right. In these cases, for optimum performance, the sensor should be placed on the higher of the two sides of the road.

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• More than a few feet – If the elevation difference is more than a few feet, more drastic measures may need to be taken; for instance, you may need to place a sensor on either side of the road to detect just that side. Unfortunately, it’s hard to say where the line is between this option and the bullet point above; it all depends on the individual installation site. Consider this diagram:

In the two examples above, the elevation difference between the two sides of the road of the road is the same. However, in the first example, the two sides of the road are farther apart; as you can see, this causes all of the lanes to fall within the radar beam of the sensor. In the second example, though, the two sides of the road are close together laterally but far apart in elevation, as can occur in areas with particularly rugged topography. In this case, as you can see, the lip of the drop between the sides of the road blocks the radar beam, causing the car close to the drop to be missed by the sensor.

This is a case in which it would be necessary to put a sensor on both sides of the road, each taking in only one side (this will, however, mean that you have a sensor facing what is essentially a vertical wall, which can cause trouble; we’ll talk about this more later). Or, if possible, choose a new spot for your sensor.  

If you’re not sure which of these two options applies to your installation, think about the installation site. If you were standing in the spot and at the height that the sensor is going to be placed, looking down at the road, could you see all the lanes, or would some of them be obscured by the change in elevation? If you can’t see all the lanes, neither can the sensor.

Are there any radar sensors on the opposite side of the road, facing your sensor?

Two radar sensors facing each other can be trouble because they can cause interference for each other. For optimal performance, sensors facing each other need to be separated by at least a 70-ft. (21.3-m) lateral offset. Move your new sensor 70 feet downstream from the facing sensor. If the lateral separation is not possible, just make sure the two sensors are set to different RF channels; this will lessen the possibility of interference.

Note. It’s fine, however, for sensors to be mounted on the same pole, whether they’re facing the same or different directions. The important thing to remember is that they must be set to different RF channels.

Are the lanes parallel in the area you’ve chosen?

Sometimes lanes are not parallel in a given spot; this is most common in the presence of an on- or off-ramp or, in the middle of a city, if the right turn lane splits off from the rest of the road. If this lane doesn’t need to be detected then you’re fine. However, if you want to detect all lanes, having one of them not parallel with the others is going to cause problems, because the sensor should be perpendicular to the flow of traffic it’s detecting.

For optimum sensor performance, then, it’d be best to install somewhere else, where all lanes are parallel. Sometimes it’s unavoidable, however.

Are there any obstacles behind the sensor’s mounting location?

One issue to be aware of as you choose an installation spot is multipathing caused by structures behind (or just very near) the sensor. Large flat structures that run parallel to the road, like buildings, retaining walls, and sounding walls are an excellent example of this; they can be especially prevalent with midblock applications in the middle of the city, where many streets are lined with buildings. Guard rails on the same side of the road as the sensor can be another issue; although they’re usually in front of the sensor, not behind it, they cause the same sorts of difficulties.

It may not seem like these obstacles could be problems—after all, they’re behind the sensor or, in the case of the guard rails, well below the sensor’s beam. The problem comes because of the way radar works. In normal operation, the sensor sends out a radar signal, which reflects off passing vehicles and is picked back up by the sensor. But what happens to that part of the signal that doesn’t get sent directly back at the sensor? It goes bouncing off into the environment around it. If that environment happens to include a sounding wall, for example, that sounding wall can bounce the signal back into the street. Once there, it might bounce off another car, and then up to the sensor. By this time, the signal has been tossed all over the street and the ranging is completely thrown off. This can cause the sensor to register these messed-up signals as vehicles that aren’t actually there. This is called multipathing.

How do we avoid this problem? Well, first, if possible, move the mounting location to one where these obstacles are not present. If it’s not possible, or if no such spot exists in the area, you can do a few things to make sure your sensor is performing as well as possible: first, get a SmartSensor HD, which is better equipped to deal with this kind of problem. Second, once your SmartSensor HD is installed, adjust the sensitivity thresholds to tune out as many of these false detections as possible. For information on how to do this, see the SmartSensor HD User Guide.

Is there a median with trees, barriers or other obstacles?

Having a median with obstacles can cause something called occlusion.

Definition. “Occlusion” refers to when tall obstacles, such as trees, signs, jersey barriers, or even semi trucks passing through, block the sensor’s view of part of the road. It’s the same as when something is in your line of sight, blocking your view of something else behind it.  

In this case we’re talking specifically about occlusion caused by barriers in the median of the road. On a freeway, these barriers are frequently jersey barriers or guard rails. In the middle of the city, this could be caused by trees or shrubs planted in the middle of the road.

Now, to some extent, this problem can be fixed by changing the mounting height of the sensor. We’ll talk about mounting heights later, but the idea is that the height can be adjusted as needed, within a set range, to get the best view of all the lanes. The rule for knowing if your sensor is at a good height (in relation to barriers or obstacles) is that 50% of a sedan needs to be visible above a barrier for it to be detected by the sensor. If the obstacle in question is jersey barriers, guard rails, shrubs or another relatively short obstacle, you may be able to mount the sensor at a height that keeps those objects from completely obstructing the sensor’s view (remembering that you must stay within the recommended range).

Note. This figure is not to scale; mounting a sensor higher requires that you also increase its offset, which we will discuss later in this lesson.

Sometimes, however, the barrier is too tall; this would be the case with trees, for instance, or possibly signs or a lot of poles. How tall is too tall? And how dense is too dense? This goes back to our visual test we were talking about earlier in the lesson: how much does the obstacle block your view? Any part of the road you can’t see will also be hidden from the sensor. If the median obstacles block the sensor’s view of the far side of the road, you’re going to have to do one of the following:  

• Move the sensor to another location where the obstacle does not exist.
• Use sensors on either side of the road, each detecting only its side of the street. In this case, see the section about facing sensors for rules governing the installation of sensors on either side of the street.
• Use one pole in the middle of the road/median with two sensors, each pointing out to a different side of the road. The advantage to this approach is that you can use the same pole for both sensors, but of course it means you need to have power and communications in the center of the road. You need to remember, however, our discussion on obstacles behind the sensor; if the barrier in the center of the road is something like a sounding wall, then putting sensors in the middle of the road is going to cause multipathing. If the barrier in the median is something large and flat, you’ll probably be better off putting the sensors on the outer edges of the road, rather than the center.

Note. If you have multiple sensors on the same pole, you’ll likely want to connect them both to the same T-bus in the pole-mount box. If you do this, you can’t have the sensors set to push data, which means they can’t be used with contact closure cards. (If you do want to use contact closure cards, you’ll need to make sure the two sensors are connected to separate buses.) We’ll talk about this in greater detail later, so for now, we just want you to be aware of it.

Are there any overhead structures in the area?

Many roads have overhead structures. These include tunnels, overpasses, pedestrian walkways, and sign bridges. These can cause detection problems for the same reason that obstacles behind the sensor can: they can reflect the radar signal around in odd ways, causing the sensor to register false detections. To avoid this problem, the sensor should be separated from such a structure by at least a 30-ft. (9.1-m) lateral offset.

If it’s impossible to choose a spot that has this 30-ft. lateral separation, consider using the SmartSensor HD and changing the sensitivity.

Are there sounding walls, guard rails, or other obstacles on the far side of the road?

This is not nearly as serious a concern as having obstacles directly behind the sensor or above the sensor. In fact, if you have to choose between having a sounding wall behind the sensor or facing the sensor, it’s better to have it facing the sensor. (For instance, in the elevation differences section, we talked about having a sensor facing a steep incline between the two sides of the road; this is preferable to having the sensor in the middle of the road with the incline behind it.) This is because when you configure your sensor, you can exclude that far area from your lane configuration.

That said, if you’re choosing between two installation spots and all other things are equal, it’d be better to choose the spot without the large obstacle on the far side of the road.  

Frequently Asked Questions

Can I paint the sensor? Many areas want to paint sensors in order to match certain color schemes as per city ordinances and other rules. This can actually cause a problem because having the sensor case another color besides white can cause the sensor to heat up to the point where it affects performance. So it’s best if you don’t paint the sensor; if it’s unavoidable, please contact Wavetronix Technical Services for further information.

Can I mount the sensor on a sounding wall? This question is sometimes asked about areas with a lot of sounding walls or similar flat surfaces along the roads, where there don’t seem to be any other places to mount. In answer to this question, we already talked at length above about the problems that accompany having flat surfaces behind the sensor—it can cause multipathing. However, if you’ve already decided that you’re comfortable with installing in such an area, and accepting the resultant potential problems, then yes, the sensor can be mounted directly onto a sounding wall. Just remember that there’s a minimum offset, meaning you need to put the sensor a short distance from the side of the road; we’ll talk about that in the next section.

What is the wind load of the sensor? This information could be useful if you intend to put a sensor in an area known for high winds. The following tables show the drag force at a variety of wind speeds; the first table shows newtons vs. kilometers per hour and the second table shows pounds vs. miles per hour.

Can I mount sensors on either side of the road for more accuracy? Using two facing sensors to detect the two sides of the road individually does lead to more accurate data. This is done in some installations where certain aspects of the mounting location lead to lower accuracy. Some of these we have talked about already. The situations where this might be useful include the following:  

• A large, sharp difference in elevation between the two sides of the road.
• Tall obstacles in the median blocking the view of the far side of the road.
• A high occurrence of semi truck traffic causing occlusion.
• A very wide road, causing the far lanes to be out of the sensor’s beam or just out on the beam’s far edge; you may recall that when a lane is on the far edge of the sensor’s view (even it’s still in the beam), the accuracy of detection for that lane is lowered.

If you do decide to put sensors on either side of the road, remember the two points we addressed in the facing sensors section earlier: set them on different RF channels, and if possible, give them a 70-ft. (21.3-m) lateral offset.

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Occupancy is calculated by summing the durations of all vehicles in the interval and dividing that quantity by the length of the interval.  

For example, if the interval length is five minutes and 100 vehicles pass the sensor during the interval with a duration of 0.09 seconds each (sum of the durations is 9 seconds), then the occupancy for that interval would be calculated by dividing 9 seconds by 300 seconds (5 minutes), which is 3%.

Rather than using the uncalibrated detection duration, or the time that a vehicle is in the radar beam, a more accurate occupancy measurement is made by first calculating the vehicle length and then converting that to a duration by adding the simulated loop size and dividing by the speed. Occupancy based on vehicle length is more accurate than occupancy based on uncalibrated detection duration because the vehicle length calculation removes the effect of the antenna beam widening as it gets farther from the sensor. The occupancy calculation is shown in the following equation:

Note that a change to the length tuning parameter for a given lane will affect the occupancy for that lane since vehicle length is used in the occupancy calculation.

The 85% column on the Interval Data screen shows the 85th percentile speed measurement. A good way to think of this is that 85% of detected vehicles are going this speed or slower; the other 15% of vehicles are going higher than this speed.

The SmartSensor HD uses the following three steps to calculate the 85th percentile speed measurement:  

1. All vehicles detected during the interval (volume) are ranked from lowest speed to highest speed.
2. The volume N is multiplied by 85% and rounded to the nearest whole number.  
3. The result in step 2 determines which vehicle’s speed from the list in step 1 is reported as the 85th percentile speed.

Example 1

During a one-minute interval, the sensor detects five vehicles with the following speeds:  

• 48 mph
• 52 mph
• 58 mph
• 48 mph  
• 39 mph  

Here’s how the sensor determines the 85th percentile speed for this interval:

1. The vehicles are ranked based on speed (lowest to highest):  

1. 39 mph
2. 48 mph
3. 48 mph
4. 52 mph
5. 58 mph

2. The volume (5) is multiplied by 85%.

5 x 0.85 = 4.25 (rounded down to 4)

3. Speed 4 is reported as the 85th percentile speed, which is 52 mph in this example.  

1. 39 mph
2. 48 mph
3. 48 mph
4. 52 mph
5. 58 mph

Example 2

If the volume (N) is a big number, for example 162, then you would use the same steps described above to find out the 85th percentile speed:

162 x 0.85 = 137.7 (rounded up to 138)

Then the 138th speed from the list of the lowest to highest speeds would be the 85th percentile speed.

Volume and Reported 85th Percentile Speed

It is possible for the 85th percentile speed to be the highest recorded speed in the interval. For this to happen, the highest speed in N vehicles must be the Nth speed from step 1. So if the Nth speed is reported as the 85the percentile speed, that means that N x (85%) is rounded up to N. Thus, the difference between N and N x (85%) should be equal or less than 0.5.

N - N x 0.85 ≤ 0.5

N ≤ 3.33

N must be an integer, so N = 1, 2 or 3.

If the second highest speed is reported as the 85th percentile speed, what is the volume (N)?

0.5 < N - N x 0.85 ≤ 1.5

3.33 < N ≤ 10

So N = 4, 5, 6, 7, 8, 9 or 10.

Based on this, we know that if the volume is 11, 12, 13, 14, 15 or 16 (10 < N ≤ 16.67), the third highest speed will be reported as the 85th percentile speed. All these are summarized in the table below:

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According to the Federal Motor Carrier Safety Administration, truck rollovers are the first harmful event in five percent of all fatal crashes involving large trucks. These rollovers are frequently caused by trucks taking curves at unsafe speeds, often on freeway on- or off-ramps.  

A contributing factor to this is that drivers may not be aware of the severity of the curve and of what is an appropriate and safe speed for the large truck they are driving. Even though speed limits are usually posted on such a curve, drivers may not notice or pay attention to these signs.

The solution? A truck rollover prevention system, which will warn individual trucks that are travelling at unsafe speeds for the approaching curve. Read on to learn how to create such a system using the Wavetronix SmartSensor HD.

1. Install SmartSensor HD

At least 350 feet before the turn in question, install a SmartSensor HD. This detector monitors up to 22 lanes of traffic across a 250-ft. range; it detects highly accurate speeds and forwards that information to a programmable controller that filters all the detections according to the length and speed of the vehicle. It can detect when trucks of a certain size, currently in an exit lane, are travelling at unsafe speeds.

For a fully self-contained installation, you can power this sensor with a solar panel, shown here; doing this means you don’t have to run power out to the sensor installation.

2. Install pole-mount box and components

On the sensor pole, install a pole-mount box. This box will serve two purposes: to provide DC power and surge protection to the sensor, and to relay detection data from the sensor to the warning system portion of the installation. The cabinet shown here contains these components:  

• A battery, for storing power from the solar panels.
• A power plant, with Click modules for using power from the battery/solar panels to safely power the sensor.
• The Click 200 surge protector. This module provides a place to quickly and easily terminate the sensor cable. This cable performs two vital functions: getting power to the sensor, and receiving detection data from the sensor. Terminating it into the Click 200 protects the sensor against surges coming from the pole-mount box.
• The Click 400, a radio that transmits detection data from the sensor to the warning system part of the installation. Using this module means you don't have to trench any communication cables.

3. Install traffic cabinet components

At the entrance of the off-ramp, place a traffic cabinet to process the data from the sensor and to power the warning sign. (Note that if no power is available at the cabinet, it is possible to set up a pole-mount solar system to power it.) This traffic cabinet should contain the following components:  

• A power plant. Like the one in the pole-mount box, this will provide clean, protected DC power to the equipment in this portion of the installation.
• A Click 400 to receive the signal from the Click 400 in the pole-mount box. This radio will put the received signal on the power and communication bus in the cabinet.
• A Click 512. This is a special module designed to trigger an alert when it receives detection data that exceeds certain user-designated thresholds. In this case, you would configure it to trigger an alert when a vehicle is detected as being in the exit lane, exceeding the size threshold that marks it as a large truck, and exceeding the speed that you’ve designated as the upper limit for safety on this particular curve. When it detects a vehicle that fits these criteria, it will trigger a contact closure alert.
• A relay, to relay said contact closure alert to the warning sign.

4. Install warning sign

The most important part here, at least for the drivers, is the warning sign. The exact layout, and the message on the sign, will vary based on your needs. The important thing is that the flashers don’t turn on unless they’ve received that alert from the Click 512. If the flashers are going constantly, they very quickly lose their impact and drivers begin to ignore them. If a driver realizes that he has personally triggered the sign, though, he’s much more likely to heed the warning and reduce his speed.

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The following shows how to wire a Wavetronix 8-conductor cable into a Click 200. If you are using an older 9-conductor cable, be aware of the following differences:

• The +485 conductor (white and blue stripe) will be solid white.
• There will be a gray GND conductor. Terminate it into the same screw terminal as -DC (black).

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The power plant is the collection of Click devices that provides power to the sensor and other Click devices. It provides surge protection and, if necessary, AC to DC power conversion (all Wavetronix devices run on DC power).

For installations supplied with AC power, the power plant includes the following:

• Click 210 circuit breaker and switch
• Click 230 AC surge module
• Click 201/202/204 AC to DC converter (in rarer cases, this could instead be the Click 203 unlimited power supply and battery)

For installations supplied with DC power, the power plant includes the following:

• Click 210 circuit breaker and switch
• Click 221 DC surge module

The most common way to obtain a power plant is to buy a preassembled backplate, of which the power plant will be part. In that case, the only setup that needs to be done is making sure that power is supplied to the backplate.

If you have purchased the individual components of the power plant, follow the steps in this document to assemble and install it.

If you have an installation with a traffic cabinet, the power plant will most likely be installed in there. If you’re just using a pole-mount box, no cabinet, that’s where the power plant should go.

Warning. An authorized electrical technician should install and operate these modules; there is a serious risk of electrical shock if the power source is handled unsafely.

AC Power Plant

Wiring in AC

1. Make sure power to AC mains is disconnected.
2. If you’re using a traffic cabinet, you will wire from its power source.
3. If you’re using a pole-mount box, push the AC power cable through one of the cable grip conduits on the bottom of the box (it’s easiest to use the bottom left). When you’re done, tighten the cable grip by twisting it until it’s tight.

Installing the Click 210

The Click 210 is a compact circuit breaker, which will interrupt an electric current if there is an overload. After a current interruption, reset the breaker by pushing the reset button (on the front of the device).

1. Mount the Click 210 onto the DIN rail.
2. Connect the line conductor (usually black) from the AC terminal block or cable to the screw terminal on the bottom of the module.
3. Connect another conductor (also black) to the screw terminal on the top of the device.

Note. For ease in troubleshooting, we recommend you follow the wire color scheme outlined here.

Installing the Click 230

1. Mount the Click 230 onto the DIN rail next to the Click 210.
2. Connect the black line conductor from the top of the Click 210 to terminal 5 on the IN side (bottom) of the Click 230. (The terminal numbers can be found on the side of the Click 230.)
3. Connect the neutral (usually white) wire from the AC terminal block or cable to the terminal marked 1 on the bottom of Click 230.
4. Connect the ground wire from the AC terminal block or cord to the terminal marked 3 on the Click 230.
5. Connect an outgoing and protected line wire (black) to the terminal marked 2 on the Click 230.
6. Connect an outgoing and protected neutral wire (white) to the terminal marked 6 on the Click 230.

Note. Terminal blocks 3 and 4 are directly bonded via the metal mounting foot of the base element to the DIN rail, so there’s no need for any additional grounding.

Installing the Click 201/202/204

The Click 201 provides 1 A (enough to power one SmartSensor HD). The Click 202 provides 2 A, and the 204 provides 4 A. Choose accordingly. (If you’re using the Click 203, see that chapter in the Click 100-400 Series User Guide.)

Follow the steps below to get power from the Click 201/202/204 to the T-bus, the power and comms bus that powers the rest of the installation:

1. Mount the Click 201/202/204 onto the DIN rail next to the Click 230.
2. Connect the line (black) wire from the Click 230 into the L screw terminal on the top of the Click 201/202/204.
3. Connect the neutral (white) wire from the Click 230 to the N screw terminal on the top of the device.
4. Connect a +DC conductor (red) to the + screw terminal on the bottom of the device.
5. Connect a -DC conductor (black) to either of the – screw terminals on the bottom of the device.
   
   Note. Don’t wire into the screw terminal marked DC OK; it provides only 20 mA and should be used only for monitoring the power supply.
   
6. Snap as many T-bus connectors as are desired onto the DIN rail and connect them together.
7. Connect a 5-screw terminal block to the end of the T-bus.
8. Connect +DC (red) from the Click 201/202/204 to the top screw terminal on the 5-screw terminal block.
9. Connect –DC (black) to the second screw terminal.

DC Power Plant

Wiring in DC

1. If you’re using a traffic cabinet, wire from its power source.
2. If you’re using a pole-mount box, feed the DC power cable through the cable grip conduit on the bottom left of the box. Tighten the grip down when you’re done.

Installing the Click 210

The Click 210 is a compact circuit breaker, which will interrupt an electric current if there is an overload. After a current interruption, reset the breaker by pushing the reset button (on the front of the device).

1. Mount the Click 210 onto the DIN rail.
2. Connect the line conductor (usually black) from the AC terminal block or cable to the screw terminal on the bottom of the module.
3. Connect another conductor (also black) to the screw terminal on the top of the device.

Note. For ease in troubleshooting, we recommend you follow the wire color scheme outlined here.

Installing the Click 221

1. Snap as many T-bus connectors as are desired onto the DIN rail and connect them together.
2. Mount the Click 221 on the first (leftmost) T-bus connector. This will connect power to the rest of the installation.
3. Connect the line (black) wire from the Click 210 into the +DC screw terminal on the bottom of the Click 221.
4. Connect the neutral (white) wire from the DC terminal block or cable to the -DC screw terminal on the bottom of the device.
5. Connect the ground conductor (green) from the DC terminal block or cable to one of the GND screw terminals on the bottom of the device.

The SmartSensor cable used to be the standard cable for SmartSensor HD, Advance, and 105 installations; although this cable has been discontinued, certain installations may still use it. This cable is sometimes referred to as the 9-conductor cable, to differentiate it from the newer 8-conductor and 6-conductor cables. This cable is composed of three groups of wires, each containing color-coded wires and a drain wire surrounded by a shield.

This diagram shows the SmartSensor cable’s 26-pin socket assignment (seen from the solder cup side of the connector).

The codes listed in the diagram are to be used to solder wires into the back of the plug where the letters represent the individual solder cups.

This figure shows the SmartSensor cable wire connections into a Click 200 surge protector.

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It’s possible to order the SmartSensor HD, V and Advance with a 26-pin connector (the connector that was used on older sensors).

See the figure below for a diagram of the 8-conductor cable’s 26-pin socket assignment. The codes listed in the diagram are to be used to solder wires into the back of the plug where the letters represent the individual solder cups.

This figure shows the 8-conductor cable wire connections into a Click 200 surge protector.

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The 8-conductor cable (used with the SmartSensor HD and V) has a 10-pin connector. This cable is composed of eight conductors plus a drain wire, all surrounded by a shield.

This diagram shows the 8-conductor cable’s 10-pin socket assignment (seen from the solder cup side of the connector). The codes listed in the diagram are to be used to solder wires into the back of the plug where the letters represent the individual solder cups.

This figure shows the 8-conductor cable wire connections into a Click 200 surge protector.

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