How to detect or judge the fault of weighbridge sensor?

Can you use the multimeter correctly to test?

According to the previous on-site maintenance experience, Quanfu can quickly solve the problems on site by using a multimeter

For the reference of weighing instrument maintenance personnel only:

1. Resistance test method: turn the range switch to 2k and measure the input and output impedance and symmetry. Take QS sensor as an example: it is normal to measure the resistance between positive excitation (+ exe) and negative excitation (- exe) at 750 ± 10 Ω; Measure the resistance between positive signal (+ SIG) and negative signal (- SIG), which is normal in the range of 703 ± 2 Ω; Four resistance values are obtained by measuring positive excitation (+ exe) and positive signal (+ SIG) and negative signal (- SIG), and negative excitation (- exe) and positive signal (+ SIG) and negative signal (- SIG). The difference between the maximum value and the minimum value is less than 1 Ω (the quantity of three-and-a-half multimeter is less than 2 Ω), which belongs to normal symmetry.

2. Other types of sensors: it is normal to measure the resistance between positive excitation (+ exe) and negative excitation (- exe) at 400 ± 10 Ω; Measure the resistance between positive signal (+ SIG) and negative signal (- SIG), which is normal in the range of 352 ± 2; Four resistance values are obtained by measuring positive excitation (+ exe) and positive signal (+ SIG) and negative signal (- SIG), and negative excitation (- exe) and positive signal (+ SIG) and negative signal (- SIG). The difference between the maximum value and the minimum value is less than 1 Ω (the quantity of three-and-a-half multimeter is less than 2 Ω), which belongs to normal symmetry. (according to the technical parameters of various sensors)

 

3. Turn the range switch to: 200m Ω resistance gear and the maximum gear. Measure the insulation resistance between the four wires of a single sensor (positive excitation + exe, negative excitation exe, positive signal + SIG and negative signal SIG) and the shielded wire. The resistance value should be greater than 200m Ω or infinity. If the resistance value is less than 200m Ω or conduction, it means that the insulation drops or conduction needs to be replaced.

 

4. Turn the range switch to: 200m Ω gear to measure the insulation resistance between a single sensor (positive excitation + exe, negative excitation exe, positive signal + SIG, negative signal SIG and shielded wire) and the sensor metal shell or scale body. The resistance value shall be greater than 200m Ω or infinity. If the resistance value is less than 200m Ω or conduction, it indicates that the insulation decreases or conduction needs to be replaced.

 

5. The above method can be used to judge the insulation resistance between the wiring terminal of PCB board of junction box and scale body (except shielding), and the insulation resistance between bus and scale body.

Note: when using the resistance gear, avoid touching the bare wire head by hand, otherwise it will be affected by the human body resistance and the wrong result will be measured.

 

6. The three insulation resistances of sensor, junction box and bus can be determined after the junction box is opened. The data drift caused by the size of insulation resistance is different, for example:

1) The water inlet insulation resistance of the junction box is on, resulting in instrument crash, instrument display with a large weight or overload alarm;

2) The damp insulation resistance of the junction box is measured within 1000 Ω, resulting in instrument data floating and unable to weigh;

3) The moisture insulation resistance of the junction box is measured within 1000 ~ 2000 Ω, which leads to the instability of the heavy weight data or the occasional data drift of the empty scale, and it will not return to zero after falling off the scale.