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KPSI™ Level & Pressure Transducers: Using Level Sensors to Monitor Water Depth in Roadside Drainage Ditches |
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You’ve seen the pictures on the evening news. Heavy rains are causing flooding and an unsuspecting motorist is caught stranded on top of his car or in a tree, while water rushes around him and rescue personnel attempt to get him to safety. The driver has misjudged the depth and force of the water covering the road, and now is at risk of losing his life. If he’s lucky, the rescue personnel will be successful. Whether the rescue is successful or not, the equipment and man-hour costs to the municipality sponsoring the operation can be overwhelming. The answer, then, is to avoid the emergency situation that arises when a road is “washed over”, by effectively monitoring water levels in roadside drainage ditches. Submersible level transducers are effective tools for monitoring water levels in roadside drainage ditches. They monitor the water level from the bottom of the ditch to the crown of the roadway, then interface with telemetry that relays information to a monitoring station. By monitoring the water levels in the ditches, and knowing the distance from the bottom of the ditch to the crown of the roadway, public safety officials can determine when a wash-over is about to occur, and dispatch crews to block off a section of a roadway, preventing disaster. How the Level Transducer Works Series 700
Ensuring Optimal Transducer Performance Ensuring optimal transducer performance begins at installation. Since electrical noise can keep the transducer from delivering an accurate signal to the monitoring station, it is important to keep this at a minimum. One way to do this is to eliminate the source of the noise altogether. When this is not possible, place the transducer as far away from the noise as is feasible. Securing the cable shield to a good earth ground is also essential. Again, use a 4-20 mA signal output, and be sure that the transducer is CE approved for electromagnetic interference. Another precaution to take during installation is to make sure that the cable does not become cut or damaged. All installation personnel should understand the importance of handling the cable with care. The cable should not be bent around rough or sharp edges. To avoid damage, use a cable reel during transport. (doesn’t apply to this application. The installation is can also be made "more friendly" to the transducer by making a small sand and gravel pit for the transducer to lay in. The transducer is placed under approximately three inches of sand, which is then covered by six inches of gravel. Once installed, a variety of occurrences may compromise the ability of the transducer to gather information and relay data accurately. Voltage spikes, for example, can prevent the transducer from delivering an accurate signal. To avoid voltage spikes, or to lessen the damage they cause, the cable shield should be connected to an earth ground as near as possible to the transmitter. It’s also a good idea to purchase a surge protection kit, which will handle typical spikes that might come in through power lines, as well as surges that travel through the ground when lightning strikes nearby. The standard water level transducer has an open-face nose piece where the diaphragm is protected by only a coarse screen. This is fine in clean water and wastewater. The former is mostly free of debris and sediment, while the latter does not contain debris that is likely to damage the diaphragm by poking through the screen and causing a rupture. In the soil, though, there are small rocks, sticks, and other debris that can get through the coarse screen of the open-face nose. This is especially likely to occur when the soil becomes saturated in a rain event. Many monitoring device manufacturers offer options that ensure smooth operation. One such option is the piezometer nose cap. This helps ensure that the transducer runs smoothly by keeping sediment in the water away from the sensor diaphragm. With the piezometer nose cap, the coarse screen is replaced with a disc that has very fine holes. These holes allow the liquid to percolate through, but keep all debris away from the sensor diaphragm. This can be a big advantage during installation, when the piezometer nose cap is instrumental in protecting the sensor diaphragm during the burial of the transducer. In most cases, both the submersible transducers and the on-site electronics are powered by a small solar panel/storage battery. Standard housings are 316 SS, because they provide effective corrosion resistance at a reasonable cost. Titanium housings are available from some manufacturers for applications in corrosive environments, such as in island communities where the water being monitored is ocean water containing a high salt content. To prevent marine growth on submersible transducers that are mounted in ditches that always contain some water, waterproof grease can be effective. Make sure that you remove the threaded nose cap to facilitate grease application, and take care not to trap air bubbles against the sensing diaphragm. As municipalities research roadside monitoring needs in their communities, they should consider the frequency with which flooding occurs, and evaluate the risks to life and property damage costs. In most cases, the short-term cost of investing in a roadside water level monitoring system is far outweighed by the long-term benefits it delivers. Submersible level transducers provide an easy, cost–effective, and reliable means of preventing a situation that can prove to be dangerous or even tragic. As seen in Water & Engineering Management – June 2001
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by Chris Lilly, Sales Engineer 
Submersible transducers, such as the KPSI Series 730, can be buried in roadside drainage ditches to monitor water levels. Reliable signal conditioning circuitry provides a 4-20 mA signal proportional to the water level above the transmitter. (The 4-20 mA is the standard signal because it is less susceptible to electrical noise/interference and can be used over longer runs of cable). The output signal is relayed via radio telemetry to a remote municipal site. At the municipal site, the signal is fed into a display with alarm capability. The alarm is set to go off slightly before the water reaches the level of the roadway. When the alarm sounds, municipality maintenance personnel head out to barricade the roads.
