How a multimeter detects a load cell
Load cells are widely used in industrial weighing (such as belt scales, floor scales, electronic scales, human scales, etc.), force testing, and tensile pressure measurement. The failure of the load cell during field use is generally as follows.
1. The sensor is overloaded, the user and the manufacturer do not communicate clearly, the sensor range and the actual force value and weight do not match, which causes the sensor to be overloaded, and the resistance of the sensor bridge arm is deformed and the circuit is unbalanced. The sensor cannot work normally, the output signal fluctuates, the resistance is infinite and so on.
2. The sensor lead is broken, and the user does not take protective measures during use. The sensor lead is broken, generally at the sensor lead interface, which affects the use of the sensor without response or sudden change in the measured value.
3. Improper use of the sensor, impact force, shear force, torsion force, etc. in the use of the static sensor seriously damage the sensor and even cannot be repaired.
So how can we effectively use the multimeter to detect the common faults of the load cell.
1. The sensor manufacturer provides the sensor output sensitivity and power supply voltage. We detect the sensor output signal according to these two parameters. Strain gauge load cell output analog signal millivolt voltage. For example, the sensor output sensitivity is 2.0mV/V, and the power supply voltage is DC10V. The two parameters can provide us with the sensor excitation operating voltage that requires DC10V. The sensor output signal corresponds to a linear relationship of 2.0mV per 1V excitation voltage output. For example, the full scale of the sensor is 50KG, then the full scale output of the DC10V voltage to the sensor is 20mV. According to this relationship, we use the multimeter mV gear to measure the sensor output signal. The no-load output of the sensor is 0mV, which is normal, which is greater than this value, but when it is close to this value, the value change means that the sensor has zero drift. If the value is large, it means that the sensor is damaged or the internal bridge is a circuit, and the bridge arm resistance is asymmetric.
2. According to the sensor parameters, input resistance and output resistance provided by the sensor factory to determine whether the sensor strain gauge is damaged. The sensor input and output resistance values are different for each manufacturer. So this should be tested according to the manufacturer's label. Use a multimeter to detect the ohm gear, the resistance of the power supply and the power supply ground, and the resistance of the signal line as well as the signal ground. If it is larger than the factory resistance value, it means that the sensor has been overloaded and the strain gauge is deformed. If the resistance value is infinite, the sensor strain gauge is seriously damaged and cannot be repaired.
3. Because the lead wire is often broken during the use of the sensor, and the outer layer of the sheath wire is intact, so the visual inspection of the sensor wire is in good condition. We use the ohmic gear of the multimeter to detect the continuity of the sensor wire. If the resistance is infinite determine the break, if the resistance changes bad contact.
