Pressure sensor

作者： PbootCMS开发版PRO 时间：2023-02-17 16:42:55 阅读：982

Pressure transducer is a device or device that can sense the pressure signal and convert the pressure signal into usable output electrical signal according to certain rules.

Pressure sensor is usually composed of pressure sensing element and signal processing unit. According to different test pressure types, pressure sensors can be divided into gauge pressure sensors, differential pressure sensors and absolute pressure sensors.

Pressure sensor is the most commonly used sensor in industrial practice. It is widely used in various industrial automation environments, including water conservancy and hydropower, railway transportation, intelligent buildings, production automation, aerospace, military, petrochemical, oil wells, electric power, ships, machine tools, pipelines and many other industries.

 

Working principle

1. Piezoresistive pressure transducer

Resistance strain gauge is one of the main components of piezoresistive strain sensor. The working principle of metal resistance strain gauge is the phenomenon that the strain resistance adsorbed on the base material changes with the mechanical deformation, commonly known as resistance strain effect.

2. Ceramic pressure sensor

The ceramic pressure sensor is based on the piezoresistive effect. The pressure directly acts on the front surface of the ceramic diaphragm, causing the diaphragm to produce small deformation. The thick film resistance is printed on the back of the ceramic diaphragm and connected to a Wheatstone bridge. Due to the piezoresistive effect of the piezoresistor, the bridge generates a highly linear voltage signal proportional to the pressure and also proportional to the excitation voltage, The standard signal is calibrated as 2.0/3.0/3.3 mV/V according to the different pressure ranges, which can be compatible with strain sensor.

3. Diffused silicon pressure sensor

The working principle of the diffused silicon pressure sensor is also based on the piezoresistive effect. Using the piezoresistive effect principle, the pressure of the measured medium directly acts on the diaphragm of the sensor (stainless steel or ceramic), making the diaphragm produce a micro-displacement proportional to the pressure of the medium, making the resistance value of the sensor change. The electronic circuit is used to detect this change and convert and output a standard measurement signal corresponding to this pressure.

4. Sapphire pressure sensor:

Based on the working principle of strain resistance type, silicon-sapphire is used as the semiconductor sensitive element, which has unparalleled metrological characteristics. Therefore, semiconductor sensitive elements made of silicon-sapphire are insensitive to temperature changes, and have good working characteristics even under high temperature conditions; Sapphire has strong radiation resistance; In addition, the silicon-sapphire semiconductor sensor has no p-n drift.

5. Piezoelectric pressure sensor:

Piezoelectric effect is the main working principle of piezoelectric sensor. Piezoelectric sensor cannot be used for static measurement, because the charge after external force is saved only when the circuit has infinite input impedance. This is not the case in practice, so this determines that piezoelectric sensors can only measure dynamic stress.

 

Unavoidable error:

When selecting the pressure sensor, we should consider its comprehensive accuracy, and which aspects will affect the accuracy of the pressure sensor? In fact, there are many factors that cause the sensor error. Now let's note four unavoidable errors, which are the initial error of the sensor.

First of all, offset error: because the vertical offset of the pressure sensor remains constant throughout the pressure range, the change of the converter diffusion and laser adjustment correction will produce offset error.

The second is the sensitivity error: the magnitude of the error is proportional to the pressure. If the sensitivity of the equipment is higher than the typical value, the sensitivity error will be an increasing function of the pressure. If the sensitivity is lower than the typical value, the sensitivity error will be a decreasing function of pressure. This error is caused by the change of diffusion process.

The third is linear error: this is a factor that has a small impact on the initial error of the pressure sensor. The reason for this error is the physical nonlinearity of the silicon chip, but for the sensor with amplifier, the nonlinearity of the amplifier should also be included. The linear error curve can be a concave curve or a convex curve load cell.

Finally, the hysteresis error: in most cases, the hysteresis error of the pressure sensor can be completely ignored, because the silicon wafer has a high mechanical stiffness. Generally, the lag error only needs to be considered when the pressure changes greatly.

The four errors of the pressure sensor cannot be avoided. We can only choose high-precision production equipment and use the latest technology to reduce these errors. We can also carry out certain error calibration when leaving the factory to reduce the errors as much as possible to meet the needs of customers.

 

Use method:

Pressure sensor is the most commonly used sensor in industrial practice. Generally, the output of ordinary pressure sensor is analog signal, which refers to the continuous signal of information parameters within a given range. Or in a continuous time interval, the characteristic quantity of its representative information can be presented as a signal of any value at any instant. The pressure sensor we usually use is mainly made of piezoelectric effect. Such sensor is also called piezoelectric sensor.

Generally, the following common sense is required when selecting:

1. Brand misunderstanding: Many times, people think that domestic products are not easy to use, or even cannot be used.

2. Misunderstanding of accuracy: When we choose products, we always think that accuracy is the most important; In fact, from a certain point of view, stability is more important than the accuracy of the product, and the selection of accuracy should be based on high stability.

3. The pursuit of cheap: good quality and cheap price is what everyone wants to see; But in fact, the high quality of the product determines that its price will be relatively high.

4. Select appropriate range, accuracy, installation mode and output mode.

The following common sense should also be understood when using:

1. Check the size of the mounting hole and keep it clean;

2. Correctly install and select the proper location;

3. Clean carefully and keep dry;

4. Avoid high and low temperature interference, high and low frequency interference and static interference;

5. Prevent pressure overload;

Pressure sensors are widely used in various industrial automation environments in China's industrial practice, involving many industries, so it is very necessary to have a comprehensive understanding of them.