9-63System ManualC79000-G8576-C199-069.5.8 Connecting a Compensating Box for Thermal E.M.F.MeasurementIf the room temperature fluctuations at the reference point (e.g. in theterminal box) affect the measurement result and you do not wish to use athermostat, you can compensate for the effect of temperature on the referencepoint with a compensating box. Between - 10 and + 70 o C, it compensates forthe change in thermal e.m.f. cause by temperature deviation (compensatingbox, see Catalog MP 11). Ensure that the compensating box has thermalcontact with the terminals.If the compensating box is aligned at 20 o C, this must be taken into accountin temperature evaluation (20 o C measuring point temperature = 0 mV).Pins 22 and 23 are extended on analog input modules as an input for thecompensating voltage. You must select a common input loop for all inputs onmode switch 2.The compensating box must be connected in a floating circuit. The powersupply unit of the compensating box must have a grounded shield winding toavoid AC system interference being picked up. A separate compensating boxwith its special power supply unit is required for each analog input module.22–ADAnalog Input ModuleMUXM–23+0 V BusM+–+PowerSupplyfor Com-pensat-ing BoxThermocoupleTerminal Box~=#RangeCard for4 Inputs6ES5 498--1AA11Compen-satingBoxFigure 9-23 Connecting a Compensating BoxAnalog Input/Output Modules
