I am trying to calibrate my 255-100 Evaporation gauge. I have taken two measurements. 2" at 31 ohms, and 8" at 543 ohms. I am using these as two points (X1,Y1) (X2,Y2) for y=mX+b slope formula. m = 0.01171875 (multiplier), and b = 1.63671875 (offset). It seems in the Novalynx manual that I can use ohms instead of mV for the X1, X2 readings, but in the CS manual it shows mV as the measurement instead. I'm not great at math, but am wondering if I shouldn't be measuring resistance but voltage instead. And if so, where exactly do I measure the voltage? I have a CR1000 if that makes any difference. Thanks in advance.. the following is my not-so-great math for the above numbers:
X1 = 31 ohms, X2 = 543 ohms, Y1 = 2", Y2 = 8"
m=(8"-2")/(543ohms-31ohms)=0.01171875
b=2"-(0.01171875 x 31ohms)=1.63671875
Did I do this right?
The readings you should use for calibration are what the datalogger reports for a multiplier of 1 and offset of 0.
Raw reading output from the half bridge measurement differs between dataloggers.
For the CR10X and CR200, raw readings are in mV.
For the CR1000, it is a ratiometric number between 0 and 1. (Signal voltage/excitation voltage)
Using measurements from the datalogger is more accurate than using a voltmeter for calibration.
With two-point calibration, you can achieve an accuracy of 1.6mm with the 255-100.