Siemens S5-135U/155U appendix Connecting a Compensating Box for Thermal E.M.F. Measurement

Analog Input/Output Modules

9.3.9Connecting a Compensating Box for Thermal E.M.F. Measurement

If the room temperature fluctuations at the reference point (e.g. in the terminal box) affect the measurement result and you do not wish to use a thermostat, you can compensate for the effect of temperature on the reference point with a compensating box. Between - 10 and + 70 oC, it compensates for the change in thermal e.m.f. cause by temperature deviation (compensating box, see Catalog MP 11). Ensure that the compensating box has thermal contact with the terminals.

If the compensating box is aligned at 20 oC, this must be taken into account in temperature evaluation (20 oC measuring point temperature = 0 mV).

Pins 22 and 23 are extended on analog input modules as an input for the compensating voltage. You must select a common input loop for all inputs on mode switch 2.

The compensating box must be connected in a floating circuit. The power supply unit of the compensating box must have a grounded shield winding to avoid AC system interference being picked up. A separate compensating box with its special power supply unit is required for each analog input module.

		Analog Input Module
Terminal Box
Thermocouple		A
	M+
		MUX
		Range
	M±	Card for
		4 Inputs
		6ES5 498-
	±	-1AA11
Compen-		#
sating
Box	+	D
	22±
	23+
		0 V Bus
Power	=
Supply
for Com-
pensat-	~
ing Box

Figure 9-8 Connecting a Compensating Box

System Manual	9-19
C79000-G8576-C199-06