Learn differential pressure transmitter types and principle

Differential pressure transmitter is the most commonly used weight transmitter in industrial practice. It is widely used in various industrial automation environments, involving 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.

How does differential pressure monitoring work?

The basic principle of the differential pressure transmitter is to divide a space sensitive element (multi-purpose bellows) into two chambers. When pressure is introduced into the two chambers, the sensor will generate displacement (or displacement) under the combined action of the two pressures. trend), this displacement is proportional to the pressure difference (differential pressure) between the two chambers, and this displacement is converted into a standard signal output that can reflect the magnitude of the differential pressure.

In the actual structure, the structure of the sensing element, the form of the chamber, the way of displacement conversion, and the format of the standard signal all have many kinds.

Pressure transmitter is an important part of process detection and control system in the automation of production process. Its function is to convert the measured process parameters such as pressure into corresponding electrical (gas) signals of the same scale, and then send this signal to other units to realize automatic detection or automatic adjustment of the above process parameters.

The working principle of the pressure transmitter is that the two pressures of the measured medium pass into the high and low pressure chambers, act on the isolation diaphragms on both sides of the sensitive element, and are transmitted to the measuring diaphragm through the isolation diaphragm and the filling liquid in the element. sides. The measuring diaphragm and the electrodes on both sides of the insulating sheet each form a capacitor.

When the pressure on both sides is inconsistent, the measuring diaphragm is displaced, and the displacement is proportional to the pressure difference, so the capacitances on both sides are not equal. Through the oscillation and demodulation links, it is converted into a signal proportional to the pressure. The working principle of pressure transmitter and absolute pressure transmitter is the same as that of differential pressure transmitter, the difference is the low pressure chamber pressure atmospheric pressure or vacuum.

The a/d converter converts the current from the demodulator into a digital signal, the value of which is used by the microprocessor to determine the input pressure value. The microprocessor controls the operation of the transmitter. Additionally, it performs sensor linearization. Reset the measurement range. Engineering unit conversion, damping, square root, sensor trimming and other operations, as well as diagnostics and array communications.

Smart differential pressure transmitter types and principles

1. Capacitive pressure transmitter working principle

When the pressure directly acts on the surface of the measuring diaphragm, the diaphragm produces a small deformation. When measuring $APPEND, the high-precision circuit on the diaphragm transforms this small deformation into a high linearity proportional to the pressure, which is also proportional to the excitation voltage. proportional to the voltage signal, and then use a special chip to convert this voltage signal into an industry-standard 4-20mA current signal or a 1-5V voltage signal.

Since the measuring diaphragm adopts a standard integrated circuit and contains linearity and temperature compensation circuits, it can achieve high precision and high stability. The transmission circuit adopts a dedicated two-wire chip, which can ensure the output of a two-wire 4-20mA current signal. , which is convenient for field wiring.

2. Diffusion silicon pressure transmitter working principle

The pressure of the measured medium acts directly on the diaphragm of the sensor (stainless steel or ceramics), causing the diaphragm to produce a micro-displacement proportional to the pressure of the medium, so that the resistance value of the sensor changes, and the electronic circuit is used to detect this change, and The conversion outputs a standard measurement signal corresponding to this pressure.

3. Ceramic pressure transmitter working principle

The pressure acts directly on the front surface of the ceramic diaphragm, causing the diaphragm to deform slightly. The thick film resistor is printed on the back of the ceramic diaphragm and connected to form a Wheatstone bridge (closed bridge). Due to the piezoresistive effect of the varistor , so that the bridge generates a highly linear voltage signal proportional to the pressure and also proportional to the excitation voltage.

4. Strain gauge pressure transmitter working principle

A resistance strain gauge is a sensitive device that converts the strain change on the measured object into an electrical signal. It is one of the main components of piezoresistive strain transmitters. 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: filamentary strain gauges and metal foil strain gauges. Usually, the strain gauge is tightly bonded to the matrix that generates mechanical strain through a special adhesive. When the stress of the matrix changes, the resistance strain gauge is also deformed together, so that the resistance value of the strain gauge changes, so that the The voltage applied to the resistor changes.