CR10X User Guide
7-12
Do not
simply copy this program without reading the
description associated with it. The multiplier for your
application will probably be different.
Please note that if you purchase the PT100 element to a
specified known tolerance, and the 100 ohm resister has an
accuracy of 0.01% or better, it is not necessary to perform the
zero calibration. A multiplier of 1.0 can be assumed.
Program
01: 3W Half Bridge (P7)
01:
1
Rep
02:
33
25mV 50Hz rejection Range
03:
3
IN Chan (single-ended channel number)
04:
1
Excite all reps w/EXchan 1
05:
2100
mV Excitation
06:
1
Loc [:Rs/Ro ]
07:
100.93
Mult
08:
0
Offset
02: Temperature RTD (P16)
01:
1
Rep
02:
1
Rs/Ro Loc [:Rs/Ro ]
03:
2
Loc [:TEMP C ]
04:
1
Mult
05:
0
Offset
7.11 100
Ω
Ω
Ω
Ω
PRT in 4-Wire Full Bridge
This example describes obtaining the temperature from a 100
Ω
PRT in a
4-wire full bridge (Instruction 6). The temperature being measured is in a constant
temperature bath and is to be used as the input for a control algorithm. The PRT
in this case does not adhere to the DIN standard (alpha = 0.00385) used in the
temperature-calculating Instruction 16. Alpha is defined as
((R
100
/R
0
)-1)/100, where R
100
and R
0
are the resistances of the PRT at 100
°
C
and 0
°
C respectively. In this PRT alpha is equal to 0.00392.
Figure 7-9 Full Bridge Schematic For 100
Ω
PRT
The result given by Instruction 6, X, is 1000 V
s
/V
x
(where V
s
is the measured
bridge output voltage and V
x
is the excitation voltage), which is:
X = 1000 (R
s
/(R
s
+R
1
)-R
3
/(R
2
+R
3
))
CAUTION
CR10X