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Products => Test Equipment => Topic started by: burnettm on June 03, 2017, 07:35:06 am

Title: Hygrometer probe for multimeter
Post by: burnettm on June 03, 2017, 07:35:06 am

Do hygrometer (relative humidity) probes which output millivolts in to banana plugs (similar to the Fluke 80TK thermocouple module) exist? If so, could anyone recommend anything affordable? I am interested in making cheese and need to monitor the humidity of the enclosure the cheese in aging in. I see cheap Chinese standalone units on Amazon which have min/max/avg functions, but if possible i'd like something which would just be a probe which I could plug in to my multimeter so I could monitor humidity without having to open the enclosure.

Title: Re: Hygrometer probe for multimeter
Post by: SeanB on June 03, 2017, 07:54:28 am

Biggest problem with cheese making is the probes will have a very short life, as the acetic acid cheese gives off during maturation will kill them pretty fast. Best is to get the cheap sensors with I2c digital outputs, and use a microcontroller to simply read the data and display it on a cheap LCD display. Then you can just have a socket and plug in the spare sensors as they die. As a bonus you also get a temperature sensor on the board as well.

Title: Re: Hygrometer probe for multimeter
Post by: burnettm on June 04, 2017, 02:23:42 am

I wasnt aware of acid problem, thanks for the info.

Title: Re: Hygrometer probe for multimeter
Post by: burnettm on June 04, 2017, 02:26:49 am

I should have also asked if you have any direct experience with this, and if so what the approximate expected lifespan of the I2C hygrometers is and what their failure modes are like. Do they just die completely or do they start giving off inaccurate readings, and if the latter is there any way to easily test/calibrate them.

Title: Re: Hygrometer probe for multimeter
Post by: SeanB on June 04, 2017, 07:44:20 am

They will get inaccurate then die with a reading that is off scale one way or the other, or with no output. Easiest way to test is to keep spares, and change them with one that is outside and next to a simple cheap all in one unit and compare readings, if they agree within 3C and 20% RH ( they really do have that unit to unit difference) then they still work, and then you can just put it back in service till it dies. Outer unit just has to be kept in a room with no drafts, and leave for around 3 hours to stabilise.

Title: Re: Hygrometer probe for multimeter
Post by: burnettm on June 05, 2017, 06:07:57 am

Thanks for the info.