The Case of the Poisoned Sensors

Sensors only have one job. But it's not always the sensor's fault for failing when it's being poisoned on duty.

In this Tip from the Field, DMS Regional Sales Manager, Justin Denson, describes how he solved a sensor situation that pitted engineering against environment…

I had a customer who was using our XNX universal transmitter with our MPD catalytic-bead sensor to detect combustible gasses. The customer was doing exactly what he was supposed to do: regularly testing the equipment to make sure that it was working properly by applying calibration gas.

But every single week he found dead sensors. He'd go in with a bottle of gas; apply gas to the sensor–and get no response. He was convinced it was a manufacturer defect.

So I went to investigate. The moment we walked into the small outdoor shed that housed the sensors, I literally tripped on cans of brake dust cleaner they were using to keep their pump clean! Hundreds of cans of this stuff littered the floor! Never mind the obvious safety hazard of this…for the moment.

I reached down to grab a can, and in really big letters on the side it said, "Contains Silicone."

The mystery was solved!

"You're poisoning these sensors," I said. "Once silicone hits the hot bead inside a catalytic-bead sensor, it encases that sensing bead with glass." The sensors were being quickly "blinded", and it's why they kept needing to be replaced all the time. An inherent limitation of cat-bead technology and one significant reason why many choose to move on to an infra-red LEL detection technology.

Although we weren't able to get the plant to change its procedures, we were able to recommend a more robust IR sensor.

Ever had a similar "environmental incompatibility" in your plant? Share with us how you discovered (and resolved) it–we'd like to feature the story in an upcoming Tips from the Field.