Sutron Corporation X-Link Operations & Maintenance Manual, Rev 1.63 5/24/2016 pg. 104
8.4.
Thermocouple Sensor
The thermocouple sensor is a common sensor for temperature readings. This
application note will show operation using the Type K thermocouple.
This sensor outputs a voltage that represents the difference in temperature from
the terminal block to the junction of the wires. Since the voltage is small,
typically uV per degrees Celsius, we will use the differential input to be able to
select a smaller scale on the A/D input, in our example we will - 39mV.
Note that the differential inputs need to be wired around mid scale of 2.5V. Vref
may be used to connect to (-) differential input to accomplish this.
Connect the sensor as follows: (See section 6.1.4.11 for more details)
Terminal Block
X-Link Description
Thermocouple
Description
4
AGND (not used)
5
VREF
, wire to DIFF ‘C’
(-)
6
DIFF ‘C’ (+)
Positive Output
7
DIFF ‘C’ (- )
Negative Output
This X-Link setup will measure the temperature difference from the sensor in
units of Celsius.
Stage Setup
Value
Active
On
Label
TDIFF
Meas Type
Analog
Analog Type
Diff C
Input Range
-39 to +39mV
Warmup
1 sec
Averaging Time 00:00:00
Slope
24716
This example uses a linear approximation for the type K thermocouple. Over the
delta T range of -8 to +64 degrees C, the error in this approximation is less than
0.3 degrees C. The linear approximation (slope) was calculated from two points:
in this case 0 degrees (0 mV) and 50 degrees (2.023 mV).
Slope = (50 degrees / 2.023 mV) * (1000 mV / V) =
24716 degrees per volt
The resultant temperature is relative to the temperature of the terminal strip to
which the thermocouple is connected. If the terminal strip is at 20C and the
thermocouple is at 30C, X-Link will read the difference (10C) in the
thermocouple.
