My TDC4 displays the warning "tOPN" even with the probe connected

Posted by Aaron on 7 August 2015

The following steps should be taken if your TDC4 displays "tOPN" even with the probe connected.

Verifying the continuity of your RTD probe:

Connect a multimeter between the two pins shown in the figure below, using the notched part of the connector for reference.  A resistance between 100 and 150 ohms indicates the probe has proper conductivity.  This does not confirm the accuracy of the probe--only it's operation.

 

RTD probe connector

Verifying the continuity of the TDC4 RTD receptacle:

Use a small length of wire and a resistor (100-150ohms) to connect the pins as shown in the figure below, using the keyed part of the receptacle for reference.  When the TDC4 is switched on it should read a small, negative value of temperature rather than the "tOPN" warning.  This does not confirm the accuracy of the TDC4 tempeture reading--only proper operation of the RTD receptacle.

 

TDC RTD receptacle