Introduction to the method of using a multimeter to detect a load cell
Industrial weighing (using devices like belt scales, floor scales, electronic scales, human scales, etc.), force testing, and tension and pressure measuring are common uses for load cells. The load cell typically fails in the following ways while being used in the field.
1. The sensor is overloaded, the user and the manufacturer have not communicated effectively, the sensor range and the real force value, as well as the weight, do not match, which results in the sensor being overloaded, causing the resistance of the sensor bridge arm to bend, and resulting in an imbalanced circuit. The output signal swings, the resistance is infinite, and other issues with the sensor prevent it from operating normally.
2. The sensor's lead wire is broken, and the user failed to take any safety precautions while using the sensor. The sensor's lead wire is damaged. Typically, the sensor cannot be used without responding, or the measured value abruptly changes, when the sensor lead wire contact breaks.
3. Misusing the sensor. The impact, shearing, and torsion forces experienced when using the static sensor gravely harm it and render it irreparable.
So how can we effectively use the multimeter to detect the common faults of the load cell on the spot?
1. Before leaving the factory, the sensor manufacturer specifies the sensor output sensitivity and power supply voltage. According to these two factors, we can detect the sensor output signal. The millivolt voltage output from the strain gauge load cell is an analog signal. For instance, the power supply voltage is DC10V and the sensor output sensitivity is 2.0mV/V. The sensor output signal corresponds to a linear relationship of 2.0 mV per 1V excitation voltage, and the sensor excitation voltage can be determined from the two parameters, which requires DC10V. For instance, if the sensor's full scale is 50KG, the full scale DC10V voltage output to the sensor is 20mV.We measure the sensor's output signal using the multimeter's mV gear in accordance with this relationship. The sensor's no-load output should typically be 0 mV, which is more than but near this figure. The value change indicates that the sensor has zero drift. The sensor is damaged or the internal bridge is a circuit if the value is high and the resistance of the bridge arm is unequal.
2. Determine whether the sensor strain gauge is damaged based on the sensor parameters, input resistance, and output resistance provided by the sensor. Manufacturers use a range of sensor input and output resistance levels. Therefore, this needs to be tested in accordance with the manufacturer's label. When using a multimeter, look for the ohm position, the power supply and ground resistance, and the signal line and ground resistance. The strain gauge is deformed and the sensor has been overloaded if it is larger than the factory resistance value. The sensor strain gauge is severely damaged and cannot be fixed if the resistance value is infinite.
3. Because the lead wire of the sensor frequently breaks when it is being used, but the outer layer of the sheath wire is still in tact, the sensor wire can be seen to be intact. The multimeter's ohm gear is used to check the sensor wire's continuity. Determine a break if the resistance is infinite; if it changes, make a poor contact.
