# How to obtain the transfer function of this sensor?

How can I obtain the transfer function(voltage to RH(%)) of this ratio-metric sensor by using the following data?:

The Vsupply might drift so I also need to include it in the equation.

• What's wrong with the 31.483 mV/%RH figure in the datasheet snippet? Jul 20, 2020 at 8:59
• It doesnt include the Vsupply and I cannot figure out the proper equation from these. I cannot be sure, Jul 20, 2020 at 9:10
• I have the cal values as in the table, but mean if the equation is like (Vout-0.826)/0.0315 for 5V supply. How will it be for 4V supply? Jul 20, 2020 at 9:27

If this was the actual calibration,

RH' = $$\\frac {V_{OUT} (5.00V/V_{SUPPLY}) - 0.826V}{0.315}\$$

So for Vsupply = 5.1V, Vout = 0.83V

RH' = (0.83V*(5V/5.1V) - 0.826V)/0.315 = 2.5% (assuming temperature is 25°C)

However you should also correct for temperature

RH = $$\\frac {RH'}{1.0546 – 0.00216T}\$$

where T is the temperature in °C

The bottom line of the table gives the information you're looking for, I think.

If you're reading this with an ADC and the ADC reference is proportional to VSUPPLY then the ratios will remain the same and you should maintain the accuracy of the readings.