Analysis of parallel knowledge of load cells
Do you know what are the three most important quality indicators for load cells? That is accuracy, stability and reliability. The gap between the load cells in the same industry is also reflected in these three aspects, so they receive special attention from users. According to relevant data surveys, the pass rate of some sensors was only 37.5%; the pass rate of electronic scales using load cells has been around 50%, and the reason for these products failing is mostly because Its temperature performance is unqualified. It can be said that this is a true reflection of the overall technical and technological level of the Chinese load cell and the overall quality level. Today, Xiaobian will share the knowledge about the parallel connection of the load cell. Come and let me know.
Assume that the sensitivity of the load cell is S1 and S2, respectively, and the bridge arm resistance is R1 and R2, respectively. The bridge voltage is U1 and U2, and the full scale is F. The condition that the two sensors work in parallel is S1R1=S2R2. Obviously, the parallel operation state requires relatively high parameters for the sensor itself. Similarly, when n load cells are operated in parallel, S1/R1=S2/R2=Sn/Rn.
The characteristics of the two sensors operating in parallel are as follows:
1) Assume that for a certain load W, we measure it with a sensor with full-scale F, sensitivity S, and bridge voltage U. The output is U1: U1=WSU/F. If the two sensors work in parallel, measure the same load W above. In the ideal case, the sensor with full scale (1/2)F can be selected. Assuming that their sensitivity is also S, the bridge voltage is also U, then total The output Un is: Un= U1 Assuming that the bridge arm resistance of both sensors is R, and the output impedance after parallel connection is Rn, then obviously Rn=R/2. Load cell
2) It can be proved that when n sensors are working in parallel, there are: Un=“U1” Rn =R /n Un=“U1” of the above formula, Rn is the output signal and output of n sensors in parallel impedance. These two equations show that no matter how many sensors work in parallel, they will not get a larger output than an equivalent sensor, but the output impedance after paralleling is reduced to 1/n of a sensor. In the case where the weighing display controller has high sensitivity or high resolution, the parallel method is better because it requires only one bridge power supply, and the system is simple and economical. However, it requires that the average deviation of the output impedance of each sensor is small, and the tolerance of the sensor coefficient should not be too large. Otherwise, when several sensors are not uniformly stressed, the average value of the output voltage will produce an error.
When connected in parallel, most of the two isolation resistors are connected between the two outputs of each splicer and the mated weighing display. Since the internal resistance of the sensor is a function of the output signal, serializing the isolation resistor reduces the effect of the resistance change on the output. The total resistance of the two isolation resistors of each sensor should be equal. The two resistors themselves should be equal and the tolerance should be small. This can reduce the influence of the sensor output impedance or the inconsistent sensor coefficient on the total output of the sensor. Tests have shown that when the sensor in parallel operation is unevenly loaded, the average error of the sensor is less than 0.05%, and R is the isolation resistance, usually about 10kO, with a tolerance of 0.01%.
The above is the parallel knowledge of the load cell, I hope to be helpful to everyone. There are small partners who need weighing sensors, you can also call us for Ocean Sensing.