Selection Criteria for Pressure/Temperature/Level Sensors

Sensors can be divided into temperature sensors (thermocouples, thermal resistances, bimetal thermometers, digital temperature indicators, etc.), pressure sensors (digital pressure gauges, pressure transmitters, differential pressure transmitters, differential pressure transmitters, high static Differential pressure transmitter, negative pressure transmitter), flow sensor (electromagnetic flow sensor, vortex flow sensor), liquid level sensor (externally mounted liquid level gauge, capacitive liquid level gauge, submerged liquid level gauge, Cable type level gauge, rod type level gauge, thread type level gauge, flange type level gauge, double flange level gauge, single flange level gauge, etc.). The sensor should be selected reasonably according to the specific measurement purpose, measurement object and measurement environment. 1 To determine the type of sensor according to the measurement object and measurement environment, a specific measurement work should be carried out. First of all, it is necessary to consider which principle sensor to use. This needs to be determined after analyzing various factors. Because, even for the measurement of the same physical quantity, there are sensors with a variety of principles to choose from. Which sensor is more suitable, you need to consider the following specific issues according to the characteristics of the measured and the conditions of use of the sensor: the size of the range; The requirements of the measured position on the sensor volume; whether the measurement method is contact or non-contact; the signal extraction method, wired or non-contact measurement; the source of the sensor, whether it is domestic or imported, and whether the price can be afforded, or self-developed. After considering the above problems, it is possible to determine which type of sensor to choose, and then consider the specific performance indicators of the sensor. 2 Selection of Sensitivity Generally, within the linear range of the sensor, it is hoped that the higher the sensitivity of the sensor, the better. Because only when the sensitivity is high, the value of the output signal corresponding to the measured change is relatively large, which is beneficial to signal processing. However, it should be noted that the sensitivity of the sensor is high, and the external noise unrelated to the measurement is also easily mixed, and it will also be amplified by the amplification system, affecting the measurement accuracy. Therefore, it is required that the sensor itself should have a high signal-to-noise ratio to minimize the disturbance signal introduced from the outside world. The sensitivity of the sensor is directional. When the measurand is a single vector, and its directivity is required to be high, the sensor with smaller sensitivity in other directions should be selected; if the measurand is a multi-dimensional vector, the smaller the cross-sensitivity of the sensor, the better. 3 Frequency response characteristics The frequency response characteristics of the sensor determine the frequency range to be measured, and the measurement conditions must be maintained without distortion within the allowable frequency range. In fact, the response of the sensor always has a certain delay, and it is hoped that the shorter the delay time, the better. The frequency response of the sensor is high, the frequency range of the measurable signal is wide, and due to the influence of the structural characteristics, the inertia of the mechanical system is large, and the frequency of the measurable signal of the sensor with low frequency is low. In dynamic measurement, should be based on the characteristics of the signal steady state, transient, random and other response characteristics, so as to avoid excessive error 4 Linear range The linear range of the sensor refers to the range in which the output is proportional to the input. Theoretically, within this range, the sensitivity remains constant. The wider the linear range of the sensor, the larger its range, and can guarantee a certain measurement accuracy. When selecting a sensor, when the type of the sensor is determined, it first depends on whether its range meets the requirements. But in fact, no sensor can guarantee perfect linearity, and its linearity is relative. When the required measurement accuracy is relatively low, within a certain range, the sensor with less nonlinear error can be approximately regarded as linear, which will bring great convenience to the measurement. 5 Stability The ability of a sensor to maintain its performance unchanged over a period of time is called stability. In addition to the structure of the sensor itself, the factors affecting the long-term stability of the sensor are mainly the use environment of the sensor. Therefore, to make the sensor have good stability, the sensor must have strong environmental adaptability. Before selecting a sensor, the use environment should be investigated, and the appropriate sensor should be selected according to the specific use environment, or appropriate measures should be taken to reduce the impact of the environment. The stability of the sensor has quantitative indicators. After the period of use, it should be re-calibrated before use to determine whether the performance of the sensor has changed. In some occasions where the sensor is required to be used for a long time but cannot be easily replaced or calibrated, the selected sensor has stricter stability requirements and must be able to withstand the test of a long time. 6 Accuracy Accuracy is an important performance index of the sensor, and it is an important link related to the measurement accuracy of the entire measurement system. The higher the accuracy of the sensor, the more expensive it is. Therefore, the accuracy of the sensor only needs to meet the accuracy requirements of the entire measurement system, and it is not necessary to select it too high. This makes it possible to choose a cheaper and simpler sensor among many sensors for the same measurement purpose. If the purpose of measurement is qualitative analysis,A sensor with continuous measurement can be selected; if it is for quantitative analysis, it is necessary to obtain accurate measurement values, and a sensor with an accuracy level that meets the requirements needs to be selected.
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