When selecting a pressure sensor, it is necessary to consider the internal elements of the sensor.
One of the many questions we often encounter in industrial production projects is what type of sensor should we choose, the characteristics of the sensor, the scale and the data requirements? Let's break down exactly the internal factors that need to be considered when selecting a pressure sensor:
Use:
1. Pressure sensors can be divided into positive pressure, relative pressure, and atmospheric pressure difference. When measuring a certain pressure, the sensor itself has a vacuum reference pressure that is independent of atmospheric pressure. The relative pressure of the atmosphere is based on the atmospheric pressure, so one side of the sensor's elastomeric membrane is always connected to the atmosphere. The atmospheric force is related to the height above ground, the different directions of the vapor content in the four seasons and the content of various gases. Therefore, the relative pressure of the measurement is related to the above factors. In addition, fluid pressure can be directed from both sides of the sensor's elastomeric membrane to confirm differences between orientations or fluids.
2. Pressure scale:
The scale of application of pressure sensors is hierarchical. This is because the elastomeric membrane of the pressure sensor is limited by the fluid pressure. This is generally referred to as the pressure limit. If this limit is exceeded, the elastomeric membrane will break. In general, the overvoltage of each sensor can be 20%-300%. Therefore, the maximum pressure scale in the product manual is 330%-80% of the withstand pressure scale.
When selecting a pressure range, three factors should be considered:
In other words, the relationship between the sensor's maximum overpressure capability and accuracy scale, as well as price and pressure scale.
In terms of static and dynamic pressure, the maximum overpressure of the sensor can vary greatly. The latter generally has impact pressure and even shock waves. The impact pressure is much higher than the static pressure. If the selected maximum working pressure scale is static pressure, the sensor should select a larger overpressure when accepting the dynamic pressure. Otherwise, the impact pressure can easily reach the limit and damage the pressure sensor.
The relationship between precision and pressure scale. Important factors that affect sensor accuracy are thermal zero drift, thermal sensitivity drift coefficient, and nonlinear error. With regard to homo-pressure sensors, thermal sensitivity coefficients and nonlinear errors are added with the addition of operating pressure. As a result, the addition of operating pressure helps to reduce thermal zero drift rather than thermal sensitivity drift and nonlinear errors. When the thermal zero drift is relatively large, adding the operating pressure scale can help improve the accuracy of the pressure sensor. The thermal zero drift is relatively small, and reducing the scale of the working pressure is conducive to improving accuracy. Sensitivity varies depending on the magnitude of the pressure. The sensitivity and high resolution of the sensor are naturally high at low pressure scales.
Generally speaking, pressure sensors below 013-1MPa are cheaper, and pressure sensors below 011MPa or above 1MPa are more expensive. When measuring 2-3kPa pressure, 10-50kPa pressure transducers can be purchased. In particular, when the user designs and selects the compensation circuits themselves, the accuracy can be further improved. This can greatly reduce the cost. In general, high-quality pressure sensors are capable of reaching 100MV/10V. If the pressure scale is only -half a year, the corresponding output is only 50MV/10V. Therefore, the maximum operating scale should be as close as possible to the size of the voltage excitation sensor specified in the product manual.
3. Sensor accuracy:
The excitation sensor can automatically control the pressure measuring element or the sensitive element. Especially with regard to previous applications, it has a relatively high accuracy requirement. The accuracy of pressure sensors made of semiconductor chips is affected by temperature, so attention should be paid to the temperature scale of the sensor.
Static accuracy refers to the accuracy that should be achieved at a specific temperature (room temperature 25°C). It can be divided into four categories: 010%-011%S is ultra-high precision: 001%-1% is high precision: 1%-2% is ordinary accuracy; 2%-2%-10% low accuracy.
Full-temperature scale accuracy refers to the accuracy that a pressure sensor should achieve over the entire operating temperature scale.
As far as users are concerned, they generally expect the higher the accuracy of the pressure sensor, the better. However, when the pressure sensor reaches high accuracy, it is necessary to add a lot of additional skills, campus composite skills and compensation skills in the production process, and add the corresponding cost. Of course, its price has also improved considerably. Therefore, reasonable accuracy requirements and corresponding temperature scales should be put forward according to the actual application and requirements of pressure sensors.
4. Voltage requirements:
Generally speaking, the output of ordinary pressure sensors is an analog signal, with a short-range full output voltage of 100-150MV and an output current of 0-0101ma. The voltage of the remote output signal will drop, and the current signal output should be used. When the exciter amplifies the current, it can output a current signal of less than 20mA. In addition, digital and frequency signals can only be obtained after A/D and V/F conversion. Constant current source and constant voltage source are the two types of encouragement sources commonly used in sensors. These two methods of encouragement are different. Encouraging a constant current source is beneficial to compensate for thermal drift.
This is because the temperature coefficient of the arm resistance is positive, while the sensitivity temperature coefficient is negative. The temperature coefficient of the output signal voltage is the algebra and algebra of both. Constant voltage encouragement does not directly provide sensitive temperature compensation. However, when a constant voltage source is used to encourage, a thermistor or diode can be connected to the bridge to compensate for the thermal drift. This sensitivity compensation method does not work when using constant current source encouragement. It is not possible to communicate constant pressure source encouragement and constant current source encouragement at will. Accuracy measurement is generally encouraged by a constant current source. In the process of constant voltage source encouragement, the measurement accuracy depends on the accuracy of the constant voltage source voltage stabilizing equipment.
It can be divided into proportional encouragement and fixed encouragement. The former is a pressure sensor bridge that is connected directly to the power supply. When the power supply changes, the sensitivity and zero point of the voltage sensor change. The latter has a reference voltage and a reference voltage to encourage a pressure sensor bridge. See Voltage constant, independent of supply voltage. As long as the supply voltage within the specified voltage scale changes, the reference voltage persists. As a result, the output of the sensor is constant and is affected by the supply voltage.
Voltage excited sensors can be battery-powered, but DC voltage stabilization is more common. Noise is low when running on battery, but as the battery is used, the supply voltage decreases, especially when the sensor is proportionally encouraged. This will result in inaccurate readings. Therefore, when measuring pressure, compensation methods (such as a common battery for pressure sensors and A/D converters) or low-power, low-current, long-life batteries or connected power supplies should be used. After measuring, turn off the battery to save power. After replacing the battery with a new one, the exciter needs to be calibrated from scratch. This is because different brands of batteries have different potentials and internal resistances. A change in the bridge encouragement voltage leads to a change in sensitivity.
5. Pressure sealing requirements: .
Rubber pads (or O-rings), epoxy resin, PTFE Zene pads, taper holes, pipe threads and welding commonly used pressure sealing materials. The operating temperature scale of the excitation sensor is determined by the sealing data.
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