Tech Tips: How to Test a Slab-SS Sensor

Hello, I'm Scott from Warmly Yours and today we're going to discuss testing the slab sensor that's used with the SCE 120 Snowmelt Controller. This sensor actually gets put into the slab or the asphalt driveway. It will tell you if the conditions are wet and how cold the conditions are. Let's take a little closer look on how to actually test both the heating element and the moisture sensor that are all built into this sensor. The first section we're going to talk about is the heating element. This unit has a heating element built into it and the reason is that when snow is falling and it hits the sensor, the snow has to be melted to make our complete circuit between the middle ring and the center ring. If this were not heating it would never melt the snow, it would never bridge this gap, and it would never turn the sensor on to tell that it was indeed wet. We should get about 224 ohms on this sensor, and if you look here we have a 220 range and a 2k range. If we set this for 200 since the reading is 224 it won't display.

Anything under 200 will show as nothing, so what we need to do is to bump it up to the 2,000 range so we can display numbers between 200 and 2,000. What I'm going to do now is to test the heating element by testing across the brown and the green wires. The next section of the sensor that we're going to be testing is the moisture sensor. The yellow wire here on the end of the wiring harness, is wired to the center section here, and the white one is wired to the middle ring. When you have dry conditions, this reading will be infinite on your ohm meter, so right now it is dry, so we should see infinite or 1 or OL or something like that displayed on the digital ohm meter. If it were wet, you would get a reading of around 100,000 ohms. To read 100,000 ohms you would need to set your digital ohm meter to the 200k range. Let's take some ice and put it on the sensor ring that will bridge the two sections together and let's see what kind of reading we get on this sensor now. You can see now that we are getting a reading. There is a bridge between the center ring and the middle ring telling us that the moisture sensor is working correctly.

That wraps up today's tech tip on how to test the slab SS sensor for your SEC 120 controller. It's a very simple thing to do. All you need is a digital ohmmeter and the end of the wire and you're set to test your slab SS. If you have any other questions, feel free to check us out at www.warmlyyours.com.