Because of the many technical goals of sensors, various data and literature have different perspectives, so that different people have different understandings, and even misunderstandings and ambiguities. To this end, the following are some of the top technical objectives of sensors:
1. Resolving power and resolution:
Resolution: Resolution refers to the smallest amount of change that can be detected by the sensor. Resolution refers to the ratio of resolution to full-scale value.
Interpretation 1: Resolution is the most basic goal of the sensor, which characterizes the sensor's ability to distinguish between the measured and measured. The other technical goals of the sensor are described in terms of resolving power as the smallest unit.
For sensors and instruments with rare functions, the resolution determines the minimum number of digits displayed in the measurement results. For example, the resolution of an electronic digital caliper is 0.01mm, and the index error is ±0.02mm.
Interpretation 2: Resolving power is a positive value with units. For example, the resolution of a temperature sensor is 0.1°C, the resolution of an accelerometer is 0.1g, and so on.
Interpretation 3: Resolution is a very similar concept related to resolution, which characterizes the sensor's ability to resolve the measurement.
The main difference between the two is that the resolution is a percentage indication of the resolving ability of the sensor, which is a relative number and has no dimension. For example, if the resolution of the above temperature sensor is 0.1°C and the full-scale range is 500°C, then its resolution is 0.1/500=0.02%.
2. Repeatability:
The repeatability of the sensor refers to the degree of difference between the measurement results when the same measurement, the same measurement, and repeated measurement along the same direction are carried out under the same conditions. It is also called repetitive error, reproduction error, etc.
Interpretation 1: The repeatability of the sensor must be the degree of difference between the results of repeated measurements obtained under the same conditions. If the measurement conditions change, the comparability between the measurement results disappears and cannot be used as a basis for checking repeatability.
Interpretation 2: The repeatability of the sensor characterizes the dispersion and randomness of the sensor's measurement results. The reason for this dispersion and randomness is that there are inevitably various random interferences inside and outside the sensor, which leads to the final measurement results of the sensor showing the characteristics of random variables.
Interpretation 3: Quantitative expression of repeatability, using the standard deviation of random variables.
Interpretation 4: In the case of repeated measurements, if the average value of all measurement results is used as the final measurement result, higher measurement accuracy can be obtained. This is because the standard deviation of the mean is significantly smaller than the standard deviation of each measure.
3. Linearity:
Linearity refers to the degree to which the input and output curves of the sensor are contrary to the straight line of ambition.
Interpretation 1: The input-output relationship of the aspiring sensor should be linear, and its input-output curve should be a straight line (the red line in the figure below).
However, there are more or less various errors in the sensors in practice, resulting in the practical input and output curve is not a straight line of ambition, but a curve (the green curve in the figure below).
Linearity is the degree of difference between the actual characteristic curve of the sensor and the off-line line, also known as nonlinearity or nonlinear error.
Interpretation 2: Because the difference between the sensor's practical characteristic curve and the ambition line is different in the case of different measurements, the ratio of the maximum value of the difference between the two in the full scale range is often used as the ratio of the maximum value of the difference between the two in the full scale range. Obviously, linearity is also a relative quantity.
Interpretation 3: Because for general measurement occasions, the aspirational straight line of the sensor is unknown and cannot be obtained. For this reason, a compromise method is often chosen, that is, the measurement results of the sensor are directly used to calculate the fitting line that is closer to the aspiration line. The detailed calculation methods include the endpoint connection method, the best straight line method, the least squares method, etc.
4. Stability:
Stability refers to the ability of a sensor to maintain its performance over a period of time.
Interpretation 1: Stability is the primary goal of investigating whether the sensor is operating stably within a certain time range. The main factors that lead to sensor instability include temperature drift and internal stress release. Therefore, adding temperature compensation, adding aging treatment and other measures are helpful to improve stability.
Interpretation 2: According to the length of the time period, stability can be divided into short-term stability and long-term stability. When the time of investigation is too short, stability and repeatability are close. Therefore, the stability objective primarily investigates long-term stability. The length of the detailed time is determined according to the operating environment and requirements.
Interpretation 3: The quantitative indication of stability objectives can be used both for positive and relative errors. For example, a strain gauge force transducer has a stability of 0.02%/12h.
5. Sampling frequency:
Sample rate refers to the amount of measurement results that the sensor can sample in a unit of time.
Interpretation 1: The sampling frequency reflects the sensor's ability to react quickly and is the most important of the dynamic characteristic targets. In the case of rapid change of measurement, sampling frequency is one of the technical goals that needs to be fully considered. According to Shannon's law of sampling, the sampling frequency of the sensor should not be less than 2 times the frequency of the measured change.
Interpretation 2: With the different frequency selected, the accuracy target of the sensor also changes accordingly. Generally speaking, the higher the sampling frequency, the lower the measurement accuracy.
The highest accuracy given by the sensor is often measured at the lowest sampling speed or even under static conditions. Therefore, it is necessary to take into account both accuracy and speed when selecting sensors.
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