User manual

Chapter 5 Transducer Conversion Functions
NI-DAQ User Manual for PC Compatibles 5-8 ni.com
Using This Function
The following equation expresses the relationship between Volts and R
t
,
the thermistor resistance (see Figure 5-2).
Volts = V
ref
( R
t
/(R
1
+ R
t
))
Solving the previous equation for R
t
,wehave:
R
t
= R
1
( Volts /(V
ref
– Volts))
After this function calculates R
t
, the function uses the following equation
to convert R
t
, the thermistor resistance, to temperature in Kelvin. The
function then converts the temperature to the temperature scale you want,
if necessary.
T=1/(a + b(ln R
t
)+c(ln R
t
)^3)
The values used for a, b,andc are given below. If you are using a thermistor
with different values for a, b ,andc (consult your thermistor data sheet),
you can edit the thermistor conversion routine to use your own a, b,and
c values.
a = 1.295361E–3
The following equation expresses the relationship between Volts and R
t
,
the thermistor resistance (see Figure 5-2).
Volts = V
ref
( R
t
/(R
1
+ R
t
))
Solving the previous equation for R
t
, you have:
R
t
= R
1
( Volts /(V
ref
– Volts))
When you calculate R
t
, you use the following equation to convert R
t
,
the thermistor resistance, to temperature in Kelvin. Then convert the
temperature to the temperature scale you want, if necessary.
T=1/(a + b(ln R
t
)+c(ln R
t
)^3)
The values used for a, b,andc are shown below. These values are correct
for the thermistors provided on the SCXI terminal blocks. If you are using
a thermistor with different values for a, b,andc (consult you thermistor