Sensor: a device or device that can sense (or respond to) the specified measured signal and convert it into usable signal output according to certain rules. The sensor is usually composed of the sensitive element which directly responds to the measured signal, the conversion element which produces the available signal output and the corresponding electronic circuit.
1. Measurement range and range:
Measurement range: the maximum measured value (i.e. input value) that the sensor can measure is called the upper limit of measurement, the minimum measured value is called the lower limit of measurement, and the measurement range expressed by the lower limit of measurement and the upper limit of measurement is called the measurement range, short for range.
The algebraic difference between the upper measurement limit and the lower measurement limit is called the range.
2. Resolution and threshold
Resolution can be expressed in two ways:
(1) The resolution expressed by the input quantity can be called the input resolution, which is defined as the minimum input quantity change that can produce the observable output quantity change in the whole working range of the sensor.
(2) The resolution expressed by the output can be called the output resolution, which is defined as the maximum step change of the output observed when the input changes slowly and continuously in the whole working range of the sensor.
Threshold value: the input value that changes from zero to make the output change observably. Commonly known as: sensitive limit, sensitive valve, failure zone, dead zone, insensitive zone, etc.
3. Sensitivity
Under the static working condition, the output produced by the unit input of the sensor becomes the sensitivity, or more strictly, the static sensitivity.
4. Hysteresis
For a certain input, the output of the sensor in the positive stroke is obviously different from that in the reverse stroke, which is called hysteresis.
5. Repeatability
Under the same working conditions, in a short time interval, when the input quantity changes from the same direction to the full scale, a group of output values corresponding to the same input quantity value are measured successively and repeatedly, and their deviation degree reflects the repeatability of the sensor.
6. Linearity
Linearity is the index to measure the performance of linear sensor. There are the following
(1) Absolute linearity: sometimes it becomes the theoretical linearity, which is the maximum deviation of the actual average output characteristic curve of the sensor from the theoretical straight line specified in its range. Expressed as a percentage of the sensor full output.
(2) End base linearity: the maximum deviation of the actual average output characteristic curve of the sensor from the end base straight line, expressed as the percentage of the full scale output of the sensor. The end base line is defined as the line connecting the first and last end of the actual average output characteristic determined by the sensor range.
(3) Zero base linearity: the maximum deviation of the actual average output characteristic curve of the sensor from the zero base straight line, expressed as the percentage of the full scale output of the sensor. The zero base line is defined as such a line, which is located in the sensor range, but can pass or extend through the theoretical zero point of the sensor, and can change its slope to minimize the maximum deviation.
(4) Independent linearity: the maximum deviation of the actual average output characteristic curve of the sensor from the best straight line, expressed as the percentage of the full scale output of the sensor. The best straight line is defined as a straight line in the middle of two parallel lines which are closest to each other and can contain all experimental points in the sensor range.
(5) Least squares linearity:
This is a straight line obtained by the least square method, so that the square sum of the deviation between the measured point and the theoretical straight line is the minimum.
7. Compliance
Most of the sensors are linear, some of them are too nonlinear, so we use curve to measure their characteristics. The so-called compliance is the degree to which the input and output characteristics of the sensor conform to or close to a reference curve.
The principles of reference curve function form are as follows:
1. It shall meet the requirements of fitting accuracy; 2. The form of function shall be as simple as possible; 3. If polynomial is used,
The frequency should be as low as possible
Like linearity, the reference for linearity is a straight line, while the reference for conformity is a curve, which has different forms as well as linearity.
8. Zero drift and temperature drift
(1) Zero time drift: it is specified that the zero drift of the sensor within one hour is the sensor drift at zero time, expressed as the percentage of the sensor’s full range.
(2) Zero temperature drift: the difference between the average output value of the zero point of the sensor at T1 and the average output value of the zero point of the sensor at T2 / (t2-t1), and the percentage of full scale at T1.
(3) Sensitivity temperature drift: the difference (t2-t1) between the sensor’s full range at T2 and T1, expressed as a percentage of the sensor’s full range at T1.
9. Total accuracy
The total accuracy is a standard for the comprehensive performance evaluation of sensors, and there are many methods. First, we provide a square and root method and algebraic sum method.
Square root method: take the square root of the sum of the three terms of hysteresis, nonlinearity (compliance) and repeatability.
Algebraic sum: that is, the algebraic sum of hysteresis, nonlinearity and repeatability.
Seccicon Global–Xin Shengkang International
Seccicon Global–Xin Shengkang International
