) You are using a load cell to measure the applied load to a test in the Civil Engineering Structures Lab. What should you do if the measured load does not return to zero? How should you troubleshoot this to determine if this is a load cell or a mechanical problem?

An insulation resistance test is carried out when there are unstable readings and random changes in the zero balance point of the load cell. It is done by measuring the resistance between the load cell body and all its connected wires, as follows:

First, disconnect the load cell from the summing box and indicator panel.

Connect all the input, output and sense (if equipped) wires together.

Measure the insulator resistance between the connected wires and the load cell body with a mega-ohmmeter.

Measure the insulation resistance between the connected wires and the cable shield.

Measure the insulation resistance between the load cell body and the cable shield.

The insulation resistance should match the value in the product’s load cell datasheet. A lower value shows an electrical leakage caused by moisture; this causes short circuits, giving unstable load cell outputs.