Section 7. Measurement Programming Examples
7-5
02:
P14
Thermocouple Temp (DIFF)
01:
5
Reps
02:
32
7.5mV 50Hz rejection Range
03:
2
IN Chan
04:
1
Type T (Copper-Constantan)
05:
1
Ref Temp Loc REF TEMP
06:
2
Loc [:TC #1 ]
07:
1
Mult
08:
0
Offset
7.4 Thermocouple Temperatures using an External
Reference Junction
When a number of thermocouple measurements is made at some distance from
the CR10X, it is often better to use a reference junction box located at the site
rather than use the 10TCRT Thermocouple Reference. Use of the external refer-
ence junction reduces the required length of expensive thermocouple wire as
ordinary copper wire can be used between the junction box (J-box) and CR10X.
In addition, if the temperature gradient between the J-box and the thermocouple
measurement junction is smaller than the gradient between the CR10X and the
measurement junction, thermocouple accuracy is improved.
In the following example, an external temperature measurement is used as the
reference for five thermocouple measurements. A Campbell Scientific 107
Temperature Probe is used to measure the reference temperature. The connection
scheme is shown in Figure 7-4.
Figure 7-4 Thermocouples with External Reference Junction
If a more accurate reference temperature is needed, use a Campbell Scientific
AM25T Solid State Multiplexer (see Section 8). The AM25T uses a 1000 ohm
PRT as the reference temperature and is designed to minimise temperature
gradients across the terminal strip.
The temperature (in
o
C) of the 107 Probe is stored in input location 1 and the
thermocouple temperatures (
o
C) in locations 2-6.
CR10X
