Humidity Sensor

[vaishnavi]

How does resistance vary when humidity/RH changes?Is there a direct or an indirect relationship in the form of a formula?

 

[CycloWizard]

It depends. Are you talking about a standard resistor or a humidistat/hygrometer/psychrometer? If you have a commercial sensor, look up the data sheet or use the calibration curve supplied. For example, look at the third page of this one:

http://www.tdk.co.jp/tefe02/eb111_chs.pdf

 

[vaishnavi]

Thankyou. Is there an equation relating resistance and humidity (RH) ?

 

[CycloWizard]

Thankyou. Is there an equation relating resistance and humidity (RH) ?

It depends. Are you talking about a standard resistor or a humidistat/hygrometer/psychrometer? If you have a commercial sensor, look up the data sheet or use the calibration curve supplied. For example, look at the third page of this one:

http://www.tdk.co.jp/tefe02/eb111_chs.pdf

 

[Modelworks]

There are also sensors that are capacitance based so it is really going to depend on the specific sensor. You can take a copper clad board , cut through the copper with a knife so you make lots of sections and measure resistance or capacitance between these sections and it will change with humidity . You will need to amplify the readings to be able to tell the difference with slight changes in humidity. There are circuits like this in the old radio shack Forest Mims books using 741 op amps

 

[dkozloski]

The basic sensor in older dial type humidity indicators was the change in length of a Norwegian blond hair with changes in humidity. No BS. As this was obviously not PC it was abondoned in favor of less suitable devices years ago.

 

[wirednuts]

It depends. Are you talking about a standard resistor or a humidistat/hygrometer/psychrometer? If you have a commercial sensor, look up the data sheet or use the calibration curve supplied. For example, look at the third page of this one:

http://www.tdk.co.jp/tefe02/eb111_chs.pdf

thats good info. do you if resistance and humidity can be related in equations?

 

[bryanl]

The basic sensor in older dial type humidity indicators was the change in length of a Norwegian blond hair with changes in humidity. No BS. As this was obviously not PC it was abondoned in favor of less suitable devices years ago.

I remember those and also sensors based on thin mylar film that could be replaced with mylar covers from TV dinners. It was essential to remove the film before cooking the dinners.

Old VCRs can be a free source of capacitive humdity sensors made of gold plated circuit board traces.