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How to Select a Pressure Sensor

When we select a pressure sensor, we may consider the following questions: Which type of pressure sensor should I choose to meet requirements? Which specifications are the most important? What conditions should be considered? This involves the selection of pressure sensors. The principle of selection is to buy pressure sensors that meet their application, measuring range, accuracy requirements, temperature range, stability, and other requirements with the most economical price. This article describes the 10 key points in the pressure sensor selection.

1. Measuring range of the pressure sensor

The first thing needs to clear is the maximum pressure value you need in the corresponding system. Then the maximum pressure of the pressure range of the selected pressure sensor should be 1.5 times the maximum pressure required by the system. These additional pressure ranges are due to the fact that many systems, especially water pressure and process control, have pressure spikes or continuous pulses. These spikes probably reach five to ten times the maximum pressure and causing the pressure sensor damage. Continuous high-voltage pulses that approach or exceed the pressure sensor's maximum rated pressure also reduce the sensor's life. Therefore, simply increasing the rated pressure of the pressure sensor is not a perfect solution, because it will sacrifice the resolution of the pressure sensor. Buffers also can be used to weaken spikes, but this is only a compromise because it will reduces the pressure sensor's response speed.

2. Measured pressure medium

What we need to consider is the measured medium of the pressure sensor. Viscous liquids and mud will block the pressure interface, and solvents or corrosive substances will damage materials in the pressure sensor that are in direct contact with these medium. These factors will determine whether to choose a direct barrier and a material that is in direct contact with the medium. The part of the general pressure sensor that contacts the medium is made of 316 stainless steel. If the measured medium is not corrosive to 316 stainless steel, basically all pressure sensors are suitable. If the measured medium is corrosive to 316 stainless steel, then it require a chemical seal, which not only measures the medium pressure, but also effectively prevents the medium from coming into contact with the liquid contact portion of the pressure sensor, thereby protecting the pressure sensor and prolonging the life of the pressure sensor.

3. Accuracy of the pressure sensor

Accuracy is a commonly used term in the industry to describe the output error of a pressure sensor. It comes from nonlinearity, hysteresis, non-reproducibility, temperature , zero balance, correction and humidity effects. Usually we specify accuracy as the combined effect of nonlinearity, hysteresis, and non-reproducibility. For many pressure sensors, the accuracy is lower than the nominal value due to factors such as temperature and zero balance. The cost of a pressure sensor with higher accuracy will be higher, but do the corresponding system really need such high accuracy ? In fact, a system that uses high- accuracy pressure sensors and low-resolution instruments is an inefficient solution.

4. Temperature range of the pressure sensor

Pressure sensors, like all physical equipment systems, can be erroneous or even unusable in extreme temperature environments. Generally all pressure sensors have two temperature ranges—the working range and the compensation range. The compensation range is included in the working range.
The working range means that within this range, the pressure sensor can be exposed to the medium without damage after it is energized. However, this does not mean that the performance of the pressure sensor can reach the nominal specification (temperature coefficient) when it is outside the compensation range.
The compensation range is generally a narrower range within the working range. Within this range, the pressure sensor can ensure that the nominal specifications are met. The change in temperature affects the pressure sensor in two ways, one is to cause zero drift, and the other is to affect the output of the entire range. Specifications of the pressure sensor should list these errors in the following form: ± x% full scale / ℃, ± x % reading / ℃, ± x % full scale over the entire temperature compensation range, or ± x % Readings over the entire temperature compensation range. If the pressure sensor don't have these parameters, it will cause you uncertainty in use. So the change in pressure sensor output due to pressure changes or temperature changes? Temperature effects will be the most complex part when understanding how to use the pressure sensor.

5. Required output signal

Generally the pressure sensor have a millivolt output, or voltage amplification, or milliamps, or frequency output. The type of output selected depends on the distance between the selected pressure sensor and the system control or display component, noise and other electrical disturbances, as well as whether amplification is required, where the amplifier is best placed, and so on. For many original equipment manufacturers, their control components and pressure sensors are very close, so millivolt output is generally sufficient and less expensive.
If the pressure sensor's output amplification is required, it is easier to use another sensor with a built-in amplifier. In long-distance cables, or areas with large electrical noise, mA output or frequency output is required. In environments with strong RF and electromagnetic interference, it is necessary to consider adding additional shielding or filtering equipment in addition to the mA and frequency outputs.

6. Select what kind of excitation voltage

The type of output signal determines which excitation voltage is selected. Some pressure sensors have built-in voltage regulators, so their supply voltage range is large. Some pressure sensors are quantitative configuration and require a stable operating voltage. Therefore, the operating voltage determines whether need to use a pressure sensor with a regulator. When selecting a pressure sensor, it is necessary to consider the operating voltage and system cost.

7. The pressure sensor stability that needs to maintain after the overtime work

Most of the pressure sensor will produce "zero drift" after overtime work, so it is necessary to grasp the stability of the pressure sensor before purchasing, which will reduce the troubles that may arise during future use.

8. Package of the pressure sensor

The package of the pressure sensor, especially often overlooked is its frame, however this will gradually reveal its shortcomings in later use. When choosing a pressure sensor, you must consider the working environment, humidity, installation, and whether there will be strong impact or vibration, etc.

9. Use what kind of connection between the pressure sensor and other electronic devices

If it need a short distance connection? If it use a long-distance connection, is it necessary to use a connector?

10. Others

After confirming the above specifications, we should confirm the process connection interface and the supply voltage of the pressure sensor. If you use it in special occasions, consider explosion protection and protection level.

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