Selection Of Various Types Of Pressure Converters, Working Methods And Methods Of Pressure Converters
Pressure transducer is a pressure measuring instrument widely used in many transducers. It is widely used in petroleum, chemical industry, metallurgy, food, power, medicine, paper making, textile and other industries. It is mainly used to measure the differential pressure, pressure, absolute pressure and water level of fluid.
- Pressure sensor components
It is mainly composed of load cell, module circuit, display instrument, panel cabinet and process connector.
It can convert the received gas, liquid and other differential pressure signals into standard current and voltage signals, and provide measurement, indication and process regulation for secondary instruments such as indicating alarm instruments, recorders and regulators.
- Measuring principle of pressure converter
The process pressure and the reference pressure act on the beam end of the integrated silicon varistor respectively, and the pressure difference deforms the silicon wafer(the position is very small μ M level only), the electric Wheatstone bridge made of semiconductor technology on the silicon chip can output the mv level voltage signal proportional to the pressure driven by the external current source.
Due to the excellent strength of silicon material, the linearity and change index of output signal are very high. When working, the pressure converter converts the measured physical quantities into mv voltage signals, which are sent to the differential amplifier with high amplification and temperature drift offset each other.
The amplified signal is converted into the corresponding current signal through voltage and current, and then the pressure and linear standard current and voltage signals are generated and input through nonlinear correction.
- Pressure sensor type
It mainly includes capacitive pressure converter, diffused silicon pressure converter, ceramic pressure converter, strain type pressure converter, etc.
3.1 Capacitive type
If the pressure acts directly on the surface of the measuring film, the film will deform slightly.
The high-precision circuit for measuring film converts small deformation into voltage signal. This voltage signal is linear and proportional to the height of the pressure, and proportional to the magnetic voltage. The voltage signal is then converted into industry standard 4-2 mA current signal or 1-5 V voltage signal by using special chips.
The measuring film adopts standardized integrated circuits, including linear and temperature compensation circuits, to ensure the high accuracy and stability of the pressure converter. The transmission circuit adopts a special two-wire chip, which can ensure the output of two-wire 4 to 2 mA current signal, and is easy to connect on site.
3.2 Silicon diffusion
The pressure of the measured medium directly acts on the film of the sensor(stainless steel or ceramic), so that the film will produce a small displacement proportional to the medium pressure, and change the resistance value of the sensor. The electronic circuit outputs the standard measurement signal corresponding to the pressure by detecting changes and converting.
3.3 Ceramic type
The ceramic pressure directly acts on the front surface of the ceramic membrane, making the membrane slightly deformed. Thick film resistance is printed on the back of ceramic film and connected with Wheatstone bridge(closed bridge). Due to the piezoresistive effect of the damper, the voltage signal generated on the bridge is highly linear, proportional to the pressure and the excitation voltage.
3.4 Contingency type
The resistance strain gauge is a sensitive element that converts the strain change of the measured part into an electrical signal. It is one of the main components of piezoresistive strain sensor.
The most widely used resistance strain gauges are metal resistance strain gauges and semiconductor strain gauges.
There are two types of metal resistance strain gauges: linear strain gauges and thin strain gauges. In general, the strain gauge is closely connected with the body and generates mechanical strain through special adhesive. When the gas stress changes, the resistance strain gauge will also deform together, changing the resistance value of the strain gauge, thus changing the voltage applied to the resistance.
- Select pressure converter
The choice of pressure converter depends on its application. According to the following choices, precision, measuring distance, output signal, medium temperature, measuring medium and explosion-proof grade.
4.1 Accuracy class
All electronic measuring instruments may have accuracy errors. When using, the transistor must be selected according to the actual accuracy requirements.
4.2 Scope
Generally, the maximum measurement range of the sensor is preferably 70% of the total sensor distance. For example, to measure a pressure of 7MPa, 10MPa must be selected as the measuring distance of the pressure transformer.
4.3 Output signal
At present, due to various acquisition needs, there are many kinds of output signals of pressure converters on the market. Mainly 4~20mA, 0~20mA, 10~10V, 1~5V, etc.
Usually 4~20mA is used. Only 4~20mA of the above output signals are of two-wire system. We say that the power is controlled first, excluding the grounding or shielding wire. The other is the three wire system.
4.4 Medium temperature
Because the signal of the pressure converter is partially converted in the electronic circuit, the measuring medium temperature of the pressure converter is usually between – 30 ° C and+100 ° C. If the temperature is too high, the condenser tube cooling medium is usually used. Compared with manufacturers specializing in producing high-temperature pressure transformers, the cost is greatly reduced.
4.5 Measuring medium
If you want to measure relatively clean fluid, you can directly use a standard pressure converter. If the measured medium is easy to crystallize or thicken, an external separation membrane or chemical seal is usually used to effectively prevent the medium from blocking the pressure measuring hole.
4.6 Other information
After determining the above five parameters, we also need to confirm the process connection interface of your pressure converter and the power supply voltage of the pressure converter. When used in special occasions, explosion-proof and protection grade shall also be considered.
- Summary
In various instruments, pressure converters are widely used. It is commonly used for measuring pressure, differential pressure, etc. Different from sensors, transistors can not only convert non electric quantity into measurable power, but also have amplification effect.
In today’s industrial world, pressure converters play an important role in industrial control systems. In addition to displaying the system pressure on the control screen, important logic calculation and parameter alarm functions are also involved.