In addition to “temperature drift”, a high-precision sensor needs to investigate far more than that, and nonlinearity is one of the important performance indicators.
Why should you be concerned about the non-linearity of pressure sensors? The pressure sensor is the core component of the pressure transmitter. At present, the commonly used pressure sensor is the piezoresistive pressure sensor, and its output signal has a large nonlinearity, which will directly affect the performance and measurement accuracy of the pressure transmitter.
So what is the nonlinearity of the sensor? By definition, the nonlinearity of the sensor means that as the pressure changes, the output of the pressure sensor presents a characteristic curve. The percentage between the maximum deviation of this curve and the fitting line and the full-scale output of the sensor is called nonlinearity. The size of this percentage determines the nonlinearity of the sensor. In a simple and intuitive understanding, it means that the degree of deviation between the output characteristic curve and the fitting straight line is nonlinear.
Why do pressure sensors have nonlinear problems? The piezoresistive pressure sensor commonly used bridge measurement circuit (Whiston bridge), as shown in the figure below,
In the initial state, the resistance values of the four bridge arms remain the same. When the input external force acts, the balanced state of the bridge arm resistance will be broken. At this time, a potential difference will appear at the output terminal. The relative change of the bridge arm resistance is in a certain proportion, and the relative change of the bridge arm resistance determines the nonlinearity of the sensor.
And each piezoresistive pressure sensor adopts some special processes in the manufacturing process, such as aging, pressure shock, welding, etc., which will have different degrees of influence on the performance of the sensor. Furthermore, in the actual production process of the diffused silicon chip, 4 It is difficult to keep the resistance value of each bridge arm absolutely consistent, so each sensor has a nominal nonlinearity.
Since nonlinearity is so important, how to calculate the nonlinear value of the sensor? First of all, let the sensor pressurize the pressure sensor under the specified temperature environment, add it from zero to full scale, reduce the pressure after the pressure is stable, and return to zero. Then, in the full range including the upper and lower limits of sensor measurement, select 6 to 11 test points evenly distributed for testing, and repeat the rise and fall calibration cycle test three or more times.
Post time: Nov-23-2022