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The working principle of the pressure transmitter
Nov 29, 2018

The working principle of the pressure transmitter


    The principle of the pressure transmitter is that the two pressures of the measured medium pass into the high and low pressure chambers, acting on the isolating diaphragms on both sides of the component (ie, the sensitive component), and transmitting to the measurement through the spacer and the filling liquid in the component. Both sides of the diaphragm. The measuring diaphragm and the electrodes on the insulating sheets on both sides each constitute a capacitor.


    When the pressures on both sides are inconsistent, the measurement diaphragm is displaced, and the displacement is proportional to the pressure difference, so the capacitance on both sides is not equal, and is converted into a signal proportional to the pressure through the oscillation and demodulation links. Pressure transmitters and absolute pressure transmitters operate on the same principle as differential pressure transmitters, except that the low pressure chamber pressure is atmospheric or vacuum.

The working principle of the pressure transmitter

    The A/D converter converts the current of the demodulator into a digital signal whose value is used by the microprocessor to determine the input pressure value. The microprocessor controls the operation of the transmitter. In addition, it performs sensor linearization. Reset the measurement range. Engineering unit conversion, damping, square root, sensor trimming and other operations, as well as diagnostic and digital communications.


    This microprocessor has a 16-byte program RAM and has three 16-bit counters, one of which performs A/D conversion.


    The D/A converter fine-tunes the data from the microprocessor and the calibrated digital signal, which can be modified by the transmitter software. The data is stored in the EEPROM and remains intact even if the power is turned off.


    The digital communication line provides the transmitter with a connection interface to an external device such as the Model 275 Smart Communicator or a control system using the HART protocol. This line detects the digital signal superimposed on the 4-20 mA signal and transmits the required information through the loop. The type of communication is the frequency shift keying FSK technology and is based on the BeII202 standard.


   Pressure transmitter is the most commonly used sensor in industrial applications. It is widely used in many industries such as water conservancy and hydropower, railway transportation, intelligent building, production automation, aerospace, military, petrochemical, oil well, electric power, ship, machine tool and pipeline.

    Pressure transmitters measure the level, density, and pressure of a liquid, gas, or vapor, and then convert the pressure signal into a 4-20mADC signal output. There are mainly capacitive pressure transmitters and diffusion silicon pressure transmitters, ceramic pressure transmitters, strain gauge pressure transmitters, etc.

   

The working principle of the pressure transmitter

 

Capacitive pressure transmitter works


    When the pressure acts directly on the surface of the measuring diaphragm to cause a slight deformation of the diaphragm, the high-precision circuit on the measuring diaphragm transforms this tiny deformation into a highly linear voltage proportional to the pressure and proportional to the excitation voltage. The signal is then converted to an industry standard 4-2OmA current signal or a 1-5V voltage signal using a dedicated chip.

    Since the measuring diaphragm adopts the standard integrated circuit and contains linear and temperature compensation circuits internally, high precision and high stability can be achieved. The transmission circuit uses a dedicated two-wire chip to ensure the output of two-wire 4-2OmA current. Signal for easy field wiring.


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Diffusion silicon pressure transmitter works


   The pressure of the measured medium acts directly on the diaphragm of the sensor (stainless steel or ceramic), causing the diaphragm to generate a micro-displacement proportional to the pressure of the medium, causing a change in the resistance value of the sensor, and detecting the change by an electronic circuit, and The conversion outputs a standard measurement signal corresponding to this pressure.


Ceramic pressure transmitter works


    

    The pressure acts directly on the front surface of the ceramic diaphragm, causing a slight deformation of the diaphragm. The thick film resistor is printed on the back side of the ceramic diaphragm and connected into a Wheatstone bridge (closed bridge) due to the piezoresistive effect of the varistor. The bridge produces a highly linear voltage signal proportional to the pressure and proportional to the excitation voltage.


Strain gauge pressure transmitter works


    A strain gage is a sensitive device that converts strain changes on a device under test into an electrical signal. It is one of the main components of a piezoresistive strain transmitter. The most widely used resistance strain gauges are metal resistance strain gauges and semiconductor strain gauges. The metal resistance strain gauge has two kinds of filament strain gauges and metal foil strain gauges. Usually, the strain gauge is tightly bonded to the mechanical strain matrix by a special adhesive. When the stress changes due to the force of the substrate, the strain gauges are also deformed together, so that the resistance of the strain gauge is changed, thereby The voltage applied to the resistor changes.


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