Troubleshooting Load Cells

Load cells are easy to troubleshoot because they act like any other resistive sensor. Since they use an exciter voltage like a Wheatstone bridge, start any troubleshooting procedure by measuring the supply voltage. If the exciter voltage is low or absent, fix this problem before continuing the troubleshooting process.

The second part of the troubleshooting process involves applying a physical load to the cell. This means you will have to look at the specifications for the load cell and apply a load that weighs approximately 50% of the maximum allowable load. The 50% load should cause the load cell to produce approximately 50% of its rated output. If the load cell specification indicates the output voltage is 3 mV volt of excitation, and the exciter voltage is 10 volts, the maximum load is 200 lb. and the test weight is 100 lb, the following formula will indicate load cell output voltage at the test weight should be approximately 15 mV when a 100 lb test weight is applied:

V_{out max} = nominal output (mV/V) x excitation voltage
V_{out max} = 3 mV/V X 10 V dc
V_{out max} = 30 mV
Output voltage _{at test weight} = (test weight / max weight) x V_{out max}
Output voltage _{at test weight} = (100 lb / 200 lb) x 30 mV = 15 mV

Exercise:

You are asked to test a load cell that has an output of 2 mV/V and an excitation voltage of 5 volts dc. The load cell has a weight capacity of 500 lb, and the test weight is 125 lb. What should the output voltage be when the 125 lb test weight is placed on the load cell?

Solution:

V_{out max} = nominal output (mV/V) X excitation voltage
V_{out max} = 2 mV/V x 5 V dc
V_{out max} = 10 mV
Output voltage _{at test weight} = (test weight / max weight) x V_{out max}
Output voltage _{at test weight} = (125 lb / 500 lb) x 10 mV = 2.5 mV

PREVIOUS: Electrical Circuits for Load Cell Sensors | NEXT: