How does a parallel load cell work?
In recent years, the qualified rate of supervision and random inspection of weighing sensor product quality is only 37.5%; The qualified rate of product quality of electronic pricing scales has been hovering around 50%, and most of the unqualified products are because the temperature performance of the weighing sensor is unqualified. It can be said that this is the overall technology and process level of China's weighing sensor, and the true reflection of the overall quality level. We assume that the sensitivity of the weighing sensor is S1 and S2, the bridge arm resistance is R1 and R2, the bridge supply voltage is U1 and U2, and the full scale is F. The condition of the two sensors working in parallel is S1R1=S2R2, obviously, the parallel working state of the sensor itself is relatively high parameter requirements.
When n load cells work in parallel, we can get: S1/R1=S2/R2=...... =Sn/Rn.
The characteristics of the two sensors working in parallel are as follows:
1) Suppose that for a certain load W, we measure it with a sensor of full scale F, sensitivity S and supply bridge voltage U, and the output is U1: U1=WSU/F.
If the two sensors work in parallel to measure the same load W above, in an ideal situation, a sensor of full scale (1/2) F can be selected, assuming that their sensitivity is also S, and the supply bridge voltage is also U, then the total output Un is: Un= U1
Assuming that the bridge arm resistance of these two sensors is R, and the output impedance after parallel is Rn, Rn=R/2 is obvious.
Similarly, it can be proved that when n sensors work in parallel, there is: Un="U1" Rn =R /n
Un="U1" and Rn are respectively the output signal and output impedance after n sensors work in parallel. These two equations show that no matter several sensors work in parallel, the output will not be larger than an equivalent sensor, but the output impedance after the parallel is reduced to 1/n of a sensor.
Under the condition that the weighing display controller has high sensitivity or high resolution, the parallel method is better, because it only needs one bridge power supply, and the system is simple and economical. However, it requires that the average deviation of each sensor output impedance should be small, and the tolerance of the sensor coefficient should not be too large. Otherwise, when several sensors are stressed unevenly, the average value of the output voltage will produce an error. When working in parallel abroad, most of the two isolation resistors are connected between the two outputs of each transmitter and the equipped weighing display. Because the internal resistance of the sensor is a function of the output signal, the influence of the resistance change on the output can be reduced by inserting the isolation resistance in series. The total resistance value of the two isolation resistors of each sensor should be equal, the two resistors themselves should be equal, and the tolerance should be small, which can reduce the influence of the sensor output impedance or the sensor coefficient inconsistency on the total output of the sensor.
