Question:
What can be the cause for an incorrect output value of the analog input module when the temperature is measured with PT100?
Answer:
Incorrect measured values can occur in case of incorrect operation / connection of the inputs.
If the inputs are assigned incorrectly, inputs resistors in the module can be damaged. Consequently, the measured value will be misinterpreted.
In order to avoid a damage of the input resistor following points are to be considered for connection / commissioning:
- First, plug the module on the backpanel bus (base supply of the module), before the external supply is connected to the front connector.
- The parameterized measuring range must correspond to the connected encoder (sensor). e. g. no parameter setting on current but application of voltage.
- At the input a voltage > 15 V is not allowed.
- Consider the instructions in the documentation for connecting the module.
If a defect occurred in the input resistors, the module can only be exchanged by a replacement device.
Such a damage can occur when e. g. a module, that has been parameterized to the signal function PT100 before, is to be used as a replacement device for voltage measurement. If first all connection cables are plugged and the supply voltage is switched (in order to parameterize the module again from the PLC program with regard to voltage measurement), voltage can be applied to the input for a certain period of time, which is still parameterized to PT 100. This voltage leads to the module's damage.
