First, I don’t know what the sensor element is (and I’ve spent some time looking!), so I have no idea how to specify it. Without a sensor that functions in the same way, the board is useless.

Second, I didn’t design the board and don’t have the right to enable people to reproduce it. I feel okay about doing a circuit analysis here, but it’s not my intent to enable duplication.

First, I have no intention of running the sensor with the screen removed, other than on my bench for long enough to measure the temperature (with my contactless infrared thermometer) in my own circuit. Then it’s back to the windscreen. Even if it increases the reaction time enough that the sensor is no longer useful to identify the point of a leak, I agree that the screen stays on.

Second, I wouldn’t care to redesign the circuit as an “installable” alarm, where failure of the circuit has safety consequences. My thoughts around making a handheld detector for a single, private use are that as long as the device itself doesn’t cause ignition (per your first point), a failure of the device is no worse than not having the device at all. And I think the device is no more likely to cause ignition than other things already present in the trailer — although it bears repeating to air out the place before trying to trace a leak.

Third, I don’t consider myself qualified to build a meter around this sensor for general, long-term use. And perhaps under those circumstances, I shouldn’t even publish information about what I do with it. But I think having a handheld version with a pot to zero the meter in the target environment, and a needle or bargraph display to show relative reading strength, could be useful for narrowing down the source of a leak.

If these caveats aren’t strong enough, I’m willing to reconsider. And thanks for raising the issues!

Firstly, do NOT run the sensor with the “windscreen” removed. While it may be more sensitive, it also may present a much higher explosion hazard if used in a explosive gas environment (which is where it’s designed to be used in anyway). The screen that first appears to be for wind, may, in fact, be designed to attenuate any flame caused by the heating element igniting a flammable atmosphere. Thus, any flash would be confined to the interior of the sensor, rather than igniting the entire environment (which includes you, the user!).

Secondly, if this device is to be used in a safety application (e.g., To keep your in-laws from blowing themselves up), you need to think through all of the possible failure modes quite carefully (as the original designers of the sensors you have appear to have done). In most test equipment, a failure is only a minor pain. In safety related test equipment, a failure may result in death.

Thirdly, even if you do build an analog version, using one of the sensors, calibrating it may be a bit of a challenge. There’s a question about how linear the sensor may be. There may also be questions about outside factors affecting the measurement (e.g., Does it measure the same in a cold environment as it does in a hot one?). There may also be issues of contamination of the sensor element (e.g., Do certain gases decompose and leave a residue on the sensor?). Plus, there’s the aging question (e.g., How does the age of the sensor affect the readings?). Designing test equipment can be fun, but it can also be a real eye-opener as to how unstable real world devices can be.

Dave