7.1.2 Load sensor

T-code Valid from serial number Date Order number

805, 813, 830 3 300 000- 2006-06-19 232020-040

One of the most important components in the weighing system is the load sensors.

A load sensor is a rectangular steel block installed inside the forks. The load sensor will be distorted 0.07 mm by a 1000 kg load. In other words, distortion of the steel block is due to the weight being lifted. The load sensor contains an electrical resistor that acts as a strain gauge.

The electrical resistor in the strain gauge present in every load sensor changes linearly in relation to the distortion of the load sensor. The load sensor has four wires connected to an indicator. The red and black wires supply power to the load sensor. The voltage fed to the load sensor is a holding current. The load sensor’s output voltage, i.e. the signal, is conducted via the green and white wires and is caused by the change in resistance in the strain gauge. With maximum load on the load sensors (e.g. 4 x 1000 kg) the signal voltage (caused by the change in the resistance) is approximately 0.01 volts. The signal voltage with a 100 kg load is only 0.0002 volts. With a load of just 1 kg, the signal voltage changes to only 0.000002 volts. When working with such weak electrical signals the wires must be in 100 % perfect condition. Bearing this in mind, the signal is transferred from the load sensors to the indicator via a special cable. All connections must be soldered and have a vapour barrier because corrosion of the terminals can otherwise result in unstable readings.

Fig. 1 Strain gauge