Environmental Technology Inc. demands the most and the best out of the products it manufactures and distributes. In a less than perfect world, however, less than ideal situations occur.
When troubleshooting the SIT-6E snow sensor, one may meet with some of these limitations. These are due to the long wire lengths between the installed sensor and the bare wire ends. That said, the following steps can be done in the field to help determine if the sensor has failed.
1. Clean the surface of the sensor with a 3M Scotch-Brite™ or similar heavy duty scrub sponge or pad with tough fibers and/or abrasives. The sensors are sometimes inadvertently sealed in the summer months when the pavement is sealed. For the sensor to work properly it must be able to detect moisture.
2. Ensure that the moisture pads have the same resistance. While there are five pads, the moisture pads are adjacent to each other (see drawing). Using an ohm-meter, test adjacent pairs until a reading is displayed. The pair should have a resistance between them of less than one ohm.
3. The three wires from the sensor are Red (24VDC), Black (24V return) and Blue (sensor signal). Measure the resistance from the red wire to the black wire going to the sensor. This resistance should be around 1200 ohms to 2400 ohms or higher. If it is lower the sensor is shorted and needs to be replaced.
4. Confirm that the controller is providing 24 V (AC or DC depending on the controller) to the point where the red wire should be connected in relation to where the black wire should go. If you do not have this voltage check for fuses providing this voltage. On the APS-C series the fuse is located on the circuit board behind the terminal block; on EUR-5s and APS-B series it will be in an inline fused holder if installed.
5. With the sensor properly connected to the controller (an APS or EUR-5 unit as note above), disconnect the red wire from the controller and place an amp meter in line between the control (supply point) and the sensor wire. You should get an initial reading of between 0.09 to 0.120 amps. After about 15 to 30 seconds it should drop to a reading of between 0.01 to 0.02 amps. If the sensor does not react in this manner then it is suspect and should be sent in for testing or replaced.
As always, you may contact ETI to address your specific concerns. Click here for information.
Scotch-Brite is a registered trademark of the 3M Company