Phidgets temp humidity sensor 1125

Supporting 10.7 and up
norman

Phidgets temp humidity sensor 1125

Postby norman » Wed Nov 24, 2010 7:06 pm

I use the formula RH (%) = (SensorValue * 0.1906) - 40.2 in the manual & I get about 10% lower readout than I should. Is this formula correct?

set val to (val * 0.1906) - 40.2

erik
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Re: Phidgets temp humidity sensor 1125

Postby erik » Thu Nov 25, 2010 10:29 am

Are you using a Phidget InterfaceKit to measure the 1125? If so, is the ratiometric setting set to true?

If you are interfacing it to your own ADC board, check the section in the product manual entitled "Other Interfacing Alternatives" in the Technical Information.

norman

Re: Phidgets temp humidity sensor 1125

Postby norman » Thu Nov 25, 2010 11:32 am

I'm using it with an 8/8/8 board, the ratiometric is set to true.

erik
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Re: Phidgets temp humidity sensor 1125

Postby erik » Thu Nov 25, 2010 12:23 pm

The formula from the product manual is very slightly off from what the chip manufacturer has provided in their data sheet. It is to compensate for some of the extra circuitry that we have included on the board. However at the same analog output value, the compensation adds only ~1%RH.

One situation where you can get such a low reading is from the humidity sensor not being powered closely enough to 5V. This can be due to long wires connecting the 1125 to the 1018, long USB cable, or even the USB hub on your computer provides less than 5V. All of these combined can dramatically change your sensor output. Use a multimeter to check the supply voltage on the 1125.

If you have an external powered USB hub, try attaching everything onto that and see if the problem persists.

norman

Re: Phidgets temp humidity sensor 1125

Postby norman » Thu Nov 25, 2010 2:36 pm

I get 5.08 vdc plugging it directly into my Mac Pro using the Phidget supplied cable.

erik
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Re: Phidgets temp humidity sensor 1125

Postby erik » Fri Nov 26, 2010 10:10 am

What are you using to compare the relative humidity to?

It could be that the board is just defective.

norman

Re: Phidgets temp humidity sensor 1125

Postby norman » Fri Nov 26, 2010 11:32 am

I'm comparing it to two other analog humidity indicators and two macTHUM humidity indicators.They all read 30% but the Phidget reads 20-21%


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