The knowledge points about pressure transmitters are infinitely endless and can be understood in depth. The pressure transmitter measurement principle is: the process pressure and the reference pressure respectively act on the two ends of the integrated silicon pressure sensitive component, and the differential pressure causes the silicon wafer to be deformed (the displacement is small, only μm level), so that the semiconductor technology on the silicon wafer is used. The resulting fully dynamic Wheatstone bridge outputs an mV-level voltage signal proportional to the pressure driven by an external current source. Due to the excellent strength of the silicon material, the linearity and variation index of the output signal are high. In operation, the pressure transmitter converts the measured physical quantity into a mV-level voltage signal and sends it to a differential amplifier with a high amplification factor that cancels the temperature drift. The amplified signal is converted into a corresponding current signal by voltage-current conversion, and then subjected to nonlinear correction, and finally a standard current-voltage signal linearly corresponding to the input pressure is generated.
How the pressure transmitter selects the output signal:
Pressure transmitter mV, V, mA and frequency output digital output, choose what output depends on a variety of factors, including the distance between the transmitter and the system controller or display, whether there is "noise" or other electronic interference signals, Whether the amplifier, the position of the amplifier, etc. are required. A transmitter with mA output is an economical and effective solution for many OEM devices with short distances between the transmitter and the controller.
In the environment with high RFI or EMI specifications, besides noting the need to select mA or frequency output, special protection or filters should be considered.
If you need to amplify the output signal, use a transmitter with built-in amplification. For long-distance transmission or strong electronic interference signals, mA-level output or frequency output is used.
Pressure transmitters are used in a wide variety of applications, and pressure transmitters are used in almost all industrial environments, as some of the problems with a wide range of pressure transmitters are obvious, which is also testing the performance of pressure transmitters. And the service life.
In the process of using the pressure transmitter, we will find that the measurement is inaccurate after the pressure transmitter is put into operation, or the signal output is unstable. In addition to its own quality problem, the interference source is generally affected by interference. The transmitter is explained in several cases of interference.
1. Radio frequency interference, mainly the start of large power equipment, interference of operation stop and high-order harmonic interference, such as interference of thyristor rectifier system.
2. Static induction of the sensor. The electrostatic induction is due to the parasitic capacitance between the two branches or components, so that the charge on one branch is transmitted to the other branch through the parasitic capacitance, so it is also called capacitive coupling.
3. Leakage current induction, due to poor insulation of component brackets, binding posts, printed circuit boards, capacitor internal media or casing inside the electronic circuit, especially the humidity of the application environment of the sensor is large, and the insulation resistance of the insulator is decreased, resulting in an increase in leakage current. It will cause interference. Especially when leakage current flows into the input stage of the measuring circuit, its effect is particularly severe.
4. Electromagnetic induction, when there is mutual inductance between two circuits, the change of current in one circuit is coupled to another circuit through the magnetic field. This phenomenon is called electromagnetic induction. For example, magnetic flux leakage of transformers and coils, parallel wires for energization, and the like.
5. Finally, there may be some other interferences. In addition to being vulnerable to the above interference, the on-site safety production monitoring system is also susceptible to mechanical interference, thermal interference and chemical interference due to poor working environment.
Pressure transmitters are different in product type and process requirements, and the price of the products is different. The manufacturer can carry out special processing according to user requirements.
First, the pressure range: that is, the small pressure and large pressure difference to be measured. The general pressure transmitter has 1.5 times overload capability.
Second, the use of temperature range: low use temperature and high use temperature. Generally it is -20 ~ 80 ° C. If the temperature is high, you need to add other cooling measures.
Third, the measured medium: With the different media, the requirements for pressure transmitters are different. For example, acid and alkali resistance, ceramic sensors are better. The outer casing is resistant to acid and alkali.
Fourth, the measurement accuracy: general use occasions, 0.5% accuracy is more. If the measurement is required to be more accurate, a measurement accuracy of 0.2%, or 0.1%, may be required.
5. Output signal: It is the signal that can be accepted by the relevant secondary instrument. Most use 4 ~ 20mA, there are other 0-5V, 0-10V or 0 ~ 20mA and other output signals.
Sixth, the interface size: according to the customer's site use conditions, processing the corresponding installation size.