Load Cell Protector

shutterstock_65960437It is the load cell’s epoxy bonding of the strain gauge that is most vulnerable. Transient voltages of 400-500V can cause the bonding to fail. As most load cells use multiple elements, this is first detected as a drift in the zero measurement. Conventional SPDs are not appropriate for load cell protection as their large series impedance affects system calibration. The purpose designed LCP01A for example, introduces less than 1 ohm series resistance per leg in the signal and sense lines, which is barely detectable as a shift in span.

The load cell protector should be installed as close as possible to each load cell and its ground connected to the load cell ground. Screened cables should be used, as the screen provides good protection against transient voltages being induced onto signal circuits. Most weighing systems use multiple load cells connecting to a field summation/junction box. A cost compromise can be made for non-critical systems by installing one load cell protector at the junction box rather than at each load cell.

At the other end of the signal cable, the measuring equipment is also vulnerable, especially the bridge signal circuit which is designed to measure voltages in the millivolt range. The LCP01A is also designed for use at the measuring equipment to protect supply, sense and signal circuits for six- or eight-wire systems.