4WPB100, 4WPB1K PRT Bridge Terminal Input Modules
9
With the PRT at 0
°
C, R
s
=R
o
. Thus, the above result becomes R
o
/R
f
, the
reciprocal of the multiplier required to calculate temperature, R
f
/R
0
. By
making a measurement with the PRT in an ice bath, errors in both R
s
and R
o
.
can be accounted for.
To perform the calibration, connect the PRT to the datalogger and program the
datalogger to measure the PRT with the 4 wire half bridge as shown in the
example section (multiplier = 1). Place the PRT in an ice bath (@ 0
°
C;
R
s
=R
0
). Read the result of the bridge measurement. The reading is R
s
/R
f
,
which is equal to R
o
/R
f
since R
s
=R
o
. The correct value of the multiplier, R
f
/R
0
,
is the reciprocal of this reading. For example, if the initial reading is 0.9890,
the correct multiplier is: R
f
/R
0
= 1/0.9890 = 1.0111.
