Pressure transmitter is a pressure signal into a standardized output signal available instrumentation, and the output signal and the pressure variable has a given continuous function relationship (usually linear function). Because of its reliable operation, high accuracy level, stable performance, strong anti-interference ability and measuring signal transmission distance and other advantages, so it is widely used in industrial field four. Its standardized output signal is mainly (0 ~ 10) mA, (4 ~ 20) mA and (1 ~ 5) V DC signal, according to different types of pressure measurement, can be divided into positive (negative) pressure transmitter, differential pressure transmitter, absolute pressure transmitter.
Common Types of Pressure Transmitters
Pressure transmitter is able to convert the pressure variable into a standard output signal instrumentation, there is a certain function relationship between the pressure variable and the output signal. According to different working principles, pressure transmitters can be divided into the following types.
Piezoresistive Pressure Transmitter
(1)Piezoresistive Pressure Transmitter is the pressure to the front surface of the diaphragm, the diaphragm under pressure will appear a certain deformation, the back of the pressure-sensitive diaphragm is printed with a thick-film resistor, which in turn forms a Wheatstone bridge, in the piezoresistive effect, the bridge will produce the corresponding voltage signals, which are proportional to the excitation voltage.
(2) Piezoelectric pressure transmitter
Piezoelectric pressure transmitter is the use of positive piezoelectric effect developed, the positive piezoelectric effect is a certain amount of external force on the electrolyte so that it deforms, the electrolyte will be polarized inside the phenomenon, and in the two surfaces of the positive and negative charges will be generated, the external force ceases to act, the electrolyte is restored to the state of the electrolyte is not charged. The polarity of the charge changes with the direction of the force. When an electric field is applied in the direction of polarity of the electrolyte, the electrolyte will be deformed, and the deformation of the electrolyte will disappear after the withdrawal of the force, which is the inverse piezoelectric effect.
(3)Strain pressure transmitter
adopts special adhesive to bond the strain gauges together to produce mechanical strain, in the body of the force changes, the resistance of the strain gauges will be followed by a certain amount of deformation, which affects the magnitude of the resistance value, the voltage on the resistor changes. But this case the resistance value of the change is small, usually composed of strain bridge, in the instrumentation amplifier under the action of the larger, and finally transmitted to the processing line display or actuator.
(4) capacitive pressure transmitter
capacitive pressure transmitter electric and pneumatic two types, the former standardized input signal for the DC signal, the latter output signal for the gas pressure. The two types of pressure of the medium to be measured were input into the high and low pressure chamber, acting on both sides of the isolation diaphragm of the sensitive element. Measuring diaphragm and both sides of the electrodes on the insulating sheet to form a capacitor, in the two sides of the pressure size is different, the module will produce displacement, the two sides of the current size is different, in the oscillation and regulation of the role of the formation of the current, voltage or digital output signal.
Pressure transmitter is an important part of the automatic control system. It is mainly used for the measurement and control of pressure parameters in industrial processes. It is widely used in the fields of petroleum, chemical industry, electric power, etc. There are many types of pressure transmitters, and they are classified in different ways according to their working principles and uses. Pressure transmitters are mainly used for remote display and control of pressure. They often work in high temperature, low pressure, corrosion, vibration and other environments, and the probability of failure is relatively high. Therefore, it is very meaningful to study the influencing factors and common failures of pressure transmitters.