semaphore TBOX LT2-530 Series User Manual page 194

Example of cabling analog inputs of –LT2 through Terminal Blocks:
GOOD
Using separate GND cables.
To measure temperature with PT1000,
a current of 0.1 mA is sent to the probe.
A variation of 1 °C corresponds to a variation
of the resistor of 3.8 Ω
With a current of 0.1 mA it gives
0.38 mV per °C
BAD
Using one GND cable.
The GND cable represents a little resistor,
common to temperature probes and sensors.
One meter of 0.5 mm² represents a resistance
of 0.034 Ω
Imagine a 4..20mA sensor returning 20mA.
20mA in a resistor of 0.034 Ω gives a voltage of
0.68 mV.
With a voltage of 0.38 mV per °C it constitutes
an error of almost 2°C on temperature inputs.
Version : 1.09
0
4
2
0
Gnd
Gnd
Pt1000
-
0
4
2
0
Gnd Gnd
Pt1000
-
1
5
3
1
+
1
5
3
1
+
194