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# Compensation resistance and selection of strain sputtering pressure sensor

Published on: June 9, 2020 by Zetian sensing

High precision sputtering sensor In the manufacturing process, a series of compensations are needed to improve the technical parameters of the sensor, including sensitivity temperature compensation, sensitivity compensation, zero balance compensation and zero temperature compensation. The following mainly introduces the various compensation methods of strain sputtering pressure sensor and the selection of compensation resistor.

(1) Sensitivity temperature compensation (also known as elastic modulus compensation): usually fixed (or combined) compensation resistor is used. Therefore, when the elastic modulus of the sensor changes, so does the sensitivity of the sensor. Therefore, the high precision sensor compensates the error. The specific method is as follows: a compensation resistor is connected in series in the bridge supply circuit, and its resistance changes with temperature and its direction is opposite to the change of sensor sensitivity to offset the drift of sensor sensitivity caused by temperature change, so as to achieve the purpose of compensation. The compensation resistance can be calculated by the formula: RM = [(S1-S2) * Rin] / {[1 + AC * (T1-T2)] * S1-S2}. Where RM is the resistance value of compensation resistor; S1 and S2 are the sensor sensitivity at temperature T1 and T2 respectively; Rin is the bridge input resistance at temperature T1; AC is the resistance temperature coefficient of compensation resistor.

(2) Sensitivity compensation: wire with smaller resistance temperature coefficient can be used. Due to the difference of elastic element material, processing size and strain gauge sensitivity coefficient, the sensitivity of the sensor is scattered (< 1%) superposition, and the sensitivity of the sensor is often relatively large. In order to improve the interchangeability of sensors, the sensitivity is designed to be slightly higher than the standard value in the manufacturing of sensors, and then it is adjusted to the standard value according to the measured results in the processing. The specific method is as follows: a compensation resistor with a smaller resistance temperature coefficient is connected in series in the bridge supply circuit to reduce the actual bridge supply voltage of the sensor, thus reducing the sensitivity of the sensor. The resistance value of compensation resistor can be calculated by formula: RC = (S1-S0) / S0 * r. Among them, RC is the resistance value of compensation resistor; S1 and S2 are the measured sensitivity before connecting RC in series and the standard sensitivity required after adjustment; R is the input resistance value of bridge circuit.

(3) Zero balance compensation: a compensation resistor with smaller temperature coefficient is usually used in series on a bridge arm in the bridge circuit, so that the output of the strain gauge bridge circuit of the sensor is approximately zero at no-load, so as to reduce the measurement error and facilitate the zero adjustment of the measuring instrument. Compensation resistors with friction type, cutting type or short circuit type are usually used, which can adjust the zero point of bridge circuit flexibly and conveniently. The friction compensation resistor can use the resistor adjusting grinding powder to grind the foil grid to adjust the resistance value; the cutting compensation resistor can adjust the resistance value by cutting the connecting grid; the short connection compensation resistor can adjust the resistance value by short connecting the grid. For example, we set the strain gauges R1 and R3 to sense the sub directional strain (negative strain), and the strain gauges R2 and R4 to sense the tensile strain (positive strain). If the zero point output is positive, then the resistance to ab terminal should be increased (that is, the resistance value will be increased by grinding), and the zero position output should be detected until the zero position output reaches zero; if the zero point output is negative, then the AC terminal resistance should be increased (that is, the resistance value will be increased by grinding), and the zero position output should be detected until the zero position output reaches zero until.

(4) Zero point temperature compensation: in order to reduce the influence of temperature on zero point output, a method of series connection of pure copper wire and nickel wire enameled wire with large resistance temperature coefficient is usually used in a bridge arm of bridge road. The no-load output of the sensor is basically zero. When the temperature of the sensor changes, on the one hand, the elastic element, adhesive and strain gauge will shrink in different degrees by thermal expansion and cooling, which will cause the change of the resistance of the strain gauge; on the other hand, the temperature coefficient of the resistance of the sensitive gate material will also change the electrical resistance of the strain gauge. All of these will affect the zero point output of the sensor. Even if the temperature self compensation strain gauge and full bridge method are used, due to the dispersion of the temperature performance of the strain gauge, the output zero position will change when the temperature changes, so it is necessary to compensate it. There are ways to do this:

Firstly, the sputtering pressure sensor is tested by temperature, and the rule of compensation resistance zero temperature drift is obtained. Then, according to the resistance corresponding to the temperature zero drift value of each sensor, the resistance value of the corresponding bridge arm compensation resistor is adjusted. The resistance value of compensation resistor can be determined by the formula:

U * - r = (T 2 /) is calculated. Where RT is the resistance value of compensation resistor; R is the resistance value of bridge arm; UIN is the bridge supply voltage; AC is the resistance temperature coefficient of compensation resistor; U1 and U2 are the zero output voltage at temperature T1 and T2 respectively. Compensation wire or compensation resistor with friction type, cutting grid type and short connection type is usually used for zero point temperature compensation.

The principle of zero temperature compensation is similar to that of zero balance compensation, but it needs to be completed in the simulated temperature field. For example, we set the strain gauges R1 and R3 to sense the sub directional strain (negative strain), and the strain gauges R2 and R4 to sense the tensile strain (positive strain). If the zero output (take positive temperature as an example, the difference between the zero output under positive temperature and the zero output at normal temperature is the zero temperature output), then the resistance at FG terminal should be increased to the calculated resistance value (that is, the resistance value is increased by grinding), then the temperature zero position output is detected and adjusted until the zero position output is consistent with the initial zero point; if the zero point output is negative Then, the EF end resistance should be increased (that is, the resistance value is increased by grinding), and then the temperature zero position output is detected and adjusted until the zero position output is consistent with the initial zero point. This article originates from Zetian sensing Please keep the source.