How to use a multimeter to test the load cell
Load cells are widely used in industrial weighing (such as belt scales, floor scales, electronic scales, human scales, etc.), force testing, and tension and 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 have not communicated clearly. The measuring range of the sensor does not match the actual force value and the weight. This causes the sensor to be overloaded, and the resistance of the bridge arm of the sensor is deformed, causing the circuit to be unbalanced. The sensor does not work normally, the output signal fluctuates, the resistance is infinite and so on.
2. The lead wire of the sensor is broken, and the user has not taken protective measures during use. The lead wire of the sensor is broken. Generally, the breakage at the interface of the sensor lead wire will affect the use of the sensor without response or the measured value will change suddenly. 3. Improper use of the sensor. During the use of the static sensor, there are impact forces, shearing forces, and torsion forces that seriously damage the sensor and cannot be repaired.
So how can we effectively use the multimeter to detect common faults of the load cell on site?
1. Sensor manufacturers provide sensor output sensitivity and power supply voltage before leaving the factory. We detect sensor output signals based on these two parameters. The strain gauge load cell outputs an 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 voltage that requires DC10V, and the sensor output signal corresponds to a linear relationship of 2.0mV per 1V excitation voltage. For example, the full scale of the sensor is 50KG, then the full scale output of DC10V voltage to the sensor is 20mV. According to this relationship, we use the multimeter mV gear to measure the output signal of the sensor. It is normal for the no-load output of the sensor to be 0mV, which is greater than this value, but close to this value, and 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 resistance of the bridge arm is asymmetrical.
2. According to the sensor parameters, input resistance and output resistance provided by the sensor factory, judge whether the sensor strain gauge is damaged. Sensor input and output resistance values vary from manufacturer to manufacturer. So this should be tested according to the manufacturer's label. Use a multimeter to detect the ohm position, the resistance of the power supply and the power ground, and the resistance of the signal line and 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, but the outer layer of the sheath wire is intact, so the sensor wire is in good condition by visual inspection. We use the ohm gear of the multimeter to detect the continuity of the sensor wire. If the resistance is infinite determine a break, if the resistance changes bad contact.
