Hi,
I am trying to measure and log RH using a Honeywell HIH-4000 series RH sensor (details here http://sensing.honeywell.com/index.cfm/ci_id/140570/la_id/1/document/1/re_id/0). The sensor requires a 5V supply, and returns a signal roughly between 1 and 4 volts that is proportional to RH. The sensor has three leads: one for 5V supply, one for ground and one for the signal voltage.
I am using a CR10 to power the sensor and read the sensor signal as a SE voltage measurement, passing through a 2:1 voltage divider to ensure the signal voltage is below 2500 mV.
When I connect the 5V supply, signal output and ground leads to the CR10 the signal output voltage is around 1.2V (corresponding to RH of about 15% - much lower than actual RH), and the signal does not respond to an changes in RH (breathing on the sensor).
However if I disconnect the signal output lead from the datalogger and measure voltage between it and AG with a digital voltmeter I get a voltage signal of around 3V (corresponding to RH of about 70%) and the signal does respond to changes in RH.
I had previously tested the sensor on a CR1000 and it worked fine.
Why would the CR10 measure a voltage between signal and ground that is different from that measured by a voltmeter?
The typical application circuit for the sensor shows a "minimum load" of 80kOhm between the signal output lead and ground - do I need to put an additional resistor between the signal and ground leads?
I'd appreciate any suggestions!
Regards,
Adrian
What is the resistance of the 2:1 divider you are using? The Campbell 2:1 divider has a resistance of 20k total which would be too low according to those specs
You will need to make another divider or use our 10:1 divider which has a 100k resistance.
Thank you for your response. The sensor did read correctly when I used a 10:1 divider.
I have seen honeywell on the following sites let me know how it is
http://www.boompack.com/en/product/honeywell-4800i-2/
http://www.boompack.com/en/product/honeywell-voyager-1202g-2/
* Last updated by: Maria12 on 2/6/2014 @ 4:55 AM *