User manual

Chapter 5 Transducer Conversion Functions
© National Instruments Corporation 5-7 NI-DAQ User Manual for PC Compatibles
Thermistor_Convert and Thermistor_Buf_Convert
These functions convert a voltage or voltage buffer read from a thermistor
into temperature. Some SCXI terminal blocks have onboard thermistors
that you can use to do cold-junction compensation.
Parameter Discussion
V
ref
is the voltage reference you apply across the thermistor circuit
(see Figure 5-2) in volts. The thermistor on the SCXI terminal blocks has
a V
ref
of 2.5 V.
R
1
is the value of the resistor in series with your thermistor (see Figure 5-2)
in ohms. The thermistor on the SCXI terminal blocks has an R
1
value of
5,000 Ω.
The TempScale integer indicates in which temperature unit you want
your return values to be. Constant definitions for each temperature scale
are assigned in the conversion header file.
1: Celsius
2: Fahrenheit
3: Kelvin
4: Rankine
The
Thermistor_Convert
function has two remaining
parameters—Volts is the voltage that you read from the thermistor,
and Temperature is the return temperature value assigned in units
determined by TempScale.
The
Thermistor_Buf_Convert
function has three remaining
parameters—numPts is the number of voltage points to convert, VoltBuf
is the array of voltages that you read from the thermistor, and TempBuf is
the return array of temperature values assigned in units determined by
TempScale.