Factors Affecting Sensor Measurement Accuracy
Release time:
2023-02-11
Generally, the actual static characteristic output of a sensor is a curve rather than a straight line. In actual work, in order for the instrument to have a uniform scale reading, a fitted straight line is often used to approximately represent the actual characteristic curve. Linearity (non-linear error) is a performance indicator of this approximation. There are several methods for selecting the fitted straight line. For example, the theoretical straight line connecting the zero input and full-scale output points can be used as the fitted straight line; or the theoretical straight line whose sum of squares of deviations from each point on the characteristic curve is minimized can be used as the fitted straight line. This fitted straight line is called the least squares fitting straight line.
1. Sensor linearity.
Normally, the actual static characteristic output of a sensor is a curve rather than a straight line. In practical applications, in order for the instrument to have a uniform scale reading, a fitting straight line is often used to approximately represent the actual characteristic curve. Linearity (nonlinear error) is a performance indicator of this approximation. There are various methods for selecting the fitting straight line. For example, the theoretical straight line connecting the zero input and full-scale output points is used as the fitting straight line; or the theoretical straight line with the minimum sum of squares of the deviations from the points on the characteristic curve is used as the fitting straight line, which is called the least squares fitting straight line.
2. Sensor sensitivity.
Sensitivity refers to the ratio of the change in output △y to the change in input △x under steady-state operating conditions. It is the slope of the output-input characteristic curve. If there is a linear relationship between the output and input of the sensor, the sensitivity S is a constant. Otherwise, it will change with the change of input. The dimension of sensitivity is the ratio of the dimensions of output and input. For example, for a certain pressure sensor, full-scale output = working voltage * sensitivity. If the working voltage is 5VDC and the sensitivity is 2mV/V, the full-scale output is 10mV. If the sensitivity is 1mV/V and the working voltage is 5VDC, the full-scale output is 5mV.
3. Sensor dynamics.
Dynamic characteristics refer to the response characteristics of the sensor to input quantities that change over time. When the dynamic characteristic input signal changes, the output signal changes correspondingly with time, and this process is called response. The dynamic characteristics of a sensor refer to the response characteristics of the sensor to input quantities that change over time. A sensor with good dynamic characteristics can accurately track the input signal in time when the input signal is a dynamic signal that changes over time, and output a signal according to the change law of the input signal. When the change of the sensor input signal is slow, it is easy to track, but as the change of the input signal accelerates, the timely tracking performance of the sensor will gradually decrease. It is usually required that the sensor can not only accurately display the magnitude of the measured quantity, but also reproduce the law of the measured quantity changing with time, which is also one of the important characteristics of the sensor.
4. Sensor stability.
Stability indicates the ability of a sensor to maintain its performance parameters over a long period of time. Ideally, the sensor's characteristic parameters do not change with time. However, in reality, the characteristics of most sensors change over time. This is because the sensitive devices or components that make up the sensor change their characteristics over time, affecting the stability of the sensor.
5. Sensor resolution.
Resolution refers to the ability of a sensor to sense the smallest change in the measured quantity. That is, if the input quantity changes slowly from a non-zero value, the output of the sensor will not change when the input change value does not exceed a certain value, that is, the sensor cannot distinguish this change in input quantity. Only when the change in input quantity exceeds the resolution will its output change. Usually, the resolution of a sensor at various points within the full scale is not the same, so the maximum change value among the input quantities that can cause a step change in the output quantity in the full scale is often used as an indicator to measure the resolution. If the above indicator is expressed as a percentage of the full scale, it is called resolution.
6. Sensor hysteresis.
Hysteresis characterizes the degree of inconsistency between the output-input characteristic curves in the forward (increasing input) and reverse (decreasing input) strokes, usually expressed as the percentage of the maximum difference △MAX between these two curves and the full-scale output F·S. Hysteresis can be caused by the absorption of energy by internal components of the sensor.
7. Sensor repeatability.
Repeatability refers to the degree of inconsistency in the characteristic curves obtained when the input quantity changes repeatedly over the full range in the same direction. The closer the characteristic curves are, the better the repeatability and the smaller the random error.
8. Sensor creep
Creep refers to the percentage of the change in pressure sensor output over time to the rated output when the load remains unchanged and other test conditions remain unchanged, generally taken as 30min.
9. Temperature influence
Changes in operating temperature will affect the zero point and sensitivity of the sensor.
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