IICTD probe erroneous reading

Good day folks,

I am using an IICTD module in a saltwater aquaculture application. I am having issues with 3 of 10 of the channels displaying whacky temp readings (around -180 to -200C). I have upgraded the firmware on the IICTD module to the latest available (the r1.3b version).

One thing I have noticed, when the entire probe is immersed, sometimes this causes the error, as opposed to submersing just the tip makes it read OK. I have tried reversing the leads assuming maybe the electrician got the leads on the module reversed but that didn’t change the reading.

Any thoughts on what might be qoing on would be appreciated.

The ICTD module reads data in uA (micro Amps) - It supplies a DC voltage and measure how much current is passing. The ICTD sensors allow 1 uA to pass per Kelvin. So if your reading is real low, then the likely issue is a bad connection - high resistance somewhere.

It is strange that reversing the connection didn’t change the reading - ICTD sensors do not conduct at all when reversed, so the reading should drop to around -274 C. I would try installing a known good sensor in the channels that are reading wrong and see what happens.

Hi Phillip,

Thanks for the response and the description of how the sensors work. When I say “didn’t change the reading” I mean faulted state. I didn’t interrogate the actual temp output. Our main page on tank status does not display the reading, just whether it is in range or faulted.

I did a review of all 10 temp readings and found that only one probe is reading close to actual (we have a handheld unit we use for verification/calibration of our old analog control system).

Only one of the tanks was at the actual measured temp, all others were a degree or two higher and one was fluctuating between 22 and 30 when the actual was 19, and the two faulted of course.

Based on how you say the sensors word, sounds like most of them are actually passing more current than they should be?

I have a tech help ticket now created, I will update this post as the situation develops.

Less, if they are reading -180 to -200.

We have two zones in our room, the first is at 17C using the handheld and the probes in that space are reading between 14 and 15C. The leads are a total of about 40’ and use 20ga wire.

The second zone is reading at 18C and the three probes in that space are all reading around 16, the extensions are also 20ga with about 60 to 70’, with soldered connections.

Would the signal be impacted by those lead lengths?

No, properly wired, that length shouldn’t be an issue.

Most manufacturers of ICTD or A/592 sensors provide a calibration offset that needs to be put into the IO unit. Typically I see the offsets between -2C and 2C. You can always calibrate yourself and enter an offset in the IO unit. Are you using a PAC or EPIC?

We are using an EPIC controller.

You can put in an offset in the channel configuration through groov manage.

That was easy, thanks. Are there any bench-top tests I can do to verify that a probe is indeed defective, with power supply and multimeter?

Yes, 9V battery in series with the sensor and a mA meter. Should read about 0.3mA at 25C