Dear all,
I'm trying to measure
temperature using a 3-wire thermistor from Li-Cor. The operation sheet
is as attached. On the DAQ side, I am using an NI 9263 to give the 5V
excitation and NI 9215 to measure the voltage output. A 'crude' wiring
diagram is as attached. As a result, I didn't get the reading that make
sense. Here are some questions I have:
1. First of all,
are the wirings correct to begin with? In one of the diagram from NI's
'How-To' guide, it says that for voltage excitation, I need to connect
a resistor (I assume a low-ohm resistor) between the +ve excitation and
the black wire. Is it suffice if I were to use a long wire to act as a
low-ohm resistor (around 2-10 Ohm)?
2. Do I need to
connect the 'com' port on the AO module to the AI module? If yes, which
port (+AI, -AI or com) should I connect to?
3. The operation sheet says that the conversion uses this equation:
Y = a0 + (a1)X + (a2)X^2 + (a3)X^3 + (a4)X^4 + (a5)X^5, where X is the uncalibrated temperature reading.
However,
in all documentations I found on the web, the equation is very
different... I think it goes something like 1/T = A + B(lnR) +
C(lnR)^3. LabVIEW's voltage to thermistor subVI also uses this
equation. The question now is, how do I relate the two equations?
Please advice. Thank you.
Shazlan
