How to use a multimeter to test weighing sensors
Weighing sensors are widely used in industrial weighing (such as belt scales, floor scales, electronic scales, human scales, etc.), force detection, and tension and pressure measurement. The faults of the weighing sensor during on-site use are generally as follows.
1. Sensor overload, unclear communication between user and manufacturer, mismatch between sensor range and actual force value, weight size, resulting in sensor overload, causing deformation of sensor bridge arm resistance and circuit imbalance. Sensors cannot function properly, output signal fluctuations, infinite resistance, and other phenomena.
2. The sensor lead is pulled apart, and the user did not take protective measures during use. The sensor lead is usually pulled apart at the sensor lead interface, which affects the sensor's use without response or sudden changes in measurement values. 3. Improper use of sensors, static sensors may suffer from severe damage such as impact, shear, and torque, making them impossible to repair.
So how can we effectively use a multimeter to detect common faults in weighing sensors on site?
1. The sensor manufacturer provides sensor output sensitivity and power supply voltage at the factory, and we detect the sensor output signal based on these two parameters. The strain gauge type weighing force sensor outputs an analog signal in millivolts. For example, the sensitivity of the sensor output is 2.0mV/V, and the power supply voltage is DC10V. The two parameters can provide us with a linear relationship between the sensor output signal and the excitation voltage output of 2.0mV per 1V. The sensor excitation working voltage requires DC10V. For example, if the sensor has a full range of 50KG, then give the sensor a full range output of 20mV with a DC10V voltage. Based on this relationship, we measure the sensor output signal using the mV gear of a multimeter. The sensor's no-load output is 0mV, which is normal. If it is greater than this value but approaches this value, a change in value indicates that the sensor has zero drift. If the value is large, it indicates that the sensor is damaged or the internal bridge is a circuit, and the bridge arm resistance is asymmetric.
2. Determine whether the sensor strain gauge is damaged based on the sensor parameters provided by the factory, input resistance, and output resistance. The input and output resistance values of sensors vary from manufacturer to manufacturer. So this needs to be tested according to the manufacturer's labeling. Use a multimeter to measure the resistance of the power supply and power ground, as well as the resistance of the signal wire and signal ground. If the resistance value is higher than the factory value, it indicates that the sensor has been overloaded and the strain gauge has deformed. If the resistance value is infinite, the sensor strain gauge is severely damaged and cannot be repaired.
3. Because the sensor often experiences wire breakage during use, and the outer layer of the protective sheath wire is intact, we visually inspect the sensor wire to see if it is intact. We use the ohmic range of a multimeter to detect the continuity of the sensor wire. If the resistance is infinite, it is determined to break, and if the resistance changes, the contact is poor.
