的被测介质的两种压力通入高、低两压力室，低压室压力采用大气压或真空，作用在δ元(即敏感元件)的两侧隔离膜片上，通过隔离片和元件内的填充液传送到测量膜片两侧。 The two pressures of the measured medium of the pressure transmitter pass into the high and low pressure chambers. The pressure in the low pressure chamber is atmospheric pressure or vacuum. The filling liquid in the element is transferred to both sides of the measuring diaphragm. The pressure transmitter is composed of a measuring diaphragm and electrodes on the insulating sheets on both sides. When the pressure on the two sides is inconsistent, the measurement diaphragm is displaced. The displacement is proportional to the pressure difference, so the capacitance on both sides is not the same. Through the oscillation and demodulation links, it is converted into a signal proportional to the pressure. The pressure transmitter's measuring part adopts a fully welded structure for the sensitive parts, and the electronic circuit part adopts wave soldering and connector installation. The overall structure is rugged, durable and has few failures. For most users, if it is found that the sensitive parts are faulty, they cannot be repaired by themselves, and the manufacturer should be contacted to replace the overall parts.
How to check the pressure transmitter: sensor check, circuit board check, field failure check.
First, how to check the pressure transmitter sensor: Failures in the measurement part of the transmitter will cause no output or abnormal output of the transmitter, so you should first check the measurement sensitive parts of the transmitter.
1. Remove the flange, and check the isolation diaphragm of the sensitive parts for deformation, damage and oil leakage. 2. Remove the compensation board, do not remove the sensitive parts, check the insulation resistance of the plug for the case, and the insulation resistance should not be less than 100MΩ when the voltage does not exceed 100V. 3． Turn on the circuit and the gas circuit. When the pressure signal is the upper limit of the range, turn off the gas source, and the output voltage and reading value should be stable. If the output voltage drops, the transmitter is leaking, and you can check the leak with soapy water.
电路板如何进行检查： How to check the pressure transmitter circuit board:
1. Turn on the power and check the status of the voltage signal at the output of the transmitter after the input pressure signal is given. If there is no output voltage, first check whether the power supply voltage is normal; whether it meets the power supply requirements; whether there is a wiring error between the power supply and the transmitter and the load equipment. If no voltage or reverse polarity is connected to the transmitter terminals, the transmitter will have no voltage signal output. Excluding the above reasons, you should further check the components of the amplifier board for damage; if there is a poor contact of the connector of the circuit board, you can compare the measured voltage of the normal instrument with the measured voltage of the faulty instrument to determine the fault. Point, if necessary, replace the faulty amplifier board. When checking the flow transmitter, pay special attention to anti-static measures for the J-type amplifier board. 2. After turning on the power, after the input pressure signal is given, if the transmitter output is too high (greater than 10VDC), or the output is too low (less than 2.0VDC), and the input pressure signal is changed and the zero and range screws are adjusted, the output does not respond. . For this kind of failure, in addition to checking whether there is any abnormality in the sensitive part of the transmitter measurement part, you should check whether the "oscillation control circuit part" on the transmitter amplifier board is working normally. The normal peak voltage between high frequency transformer T1-12 should be 25 ~ 35VP-P; the frequency is about 32kHz. Secondly, check the working conditions of the operational amplifiers on the amplifier board; whether the components of each part are damaged. This type of failure requires the amplifier board to be replaced. 3． The transmitter is very strict in the design of the circuit and the quality of the process assembly. In actual use, for the line failure that occurs, it is best to contact the manufacturer to replace the faulty circuit board after inspection and confirmation to ensure the long-term stability of the instrument. And reliability.
现场故障如何进行检查：施工现场出现的故障，绝大多数是由于使用和安装方法不当引起的，归纳起来有几个方面。 Third, how to check the pressure transmitter on-site failures: Most of the failures at the construction site are caused by improper use and installation methods. There are several aspects to summarize.
1. The primary component (orifice plate, remote measurement connector, etc.) is blocked or installed incorrectly, and the pressure point is not reasonable. 2. Leakage or blockage of the impulse tube, residual gas in the liquid-filled tube or residual liquid in the gas-filled tube, and deposits in the process flange of the transmitter, forming a measurement dead zone. 3． The transmitter wiring is incorrect, the power supply voltage is too high or too low, indicating that the connection between the meter head and the instrument terminal is bad. 4． The installation was not strictly in accordance with the technical requirements, and the installation method and site environment did not meet the technical requirements. The above failures will cause the transmitter to output abnormally or inaccurately. However, after careful inspection, use and installation strictly in accordance with technical requirements, and take effective measures in a timely manner, the problem can be ruled out. For failures that cannot be handled, it should be changed The device is sent to the laboratory or manufacturer for further inspection. The pressure transmitter is used to measure the level, density and pressure of liquid, gas or steam, and then convert the pressure signal into a 4-20mA DC signal output. Pressure transmitters mainly include capacitive pressure transmitters and diffused silicon pressure transmitters, ceramic pressure transmitters, and strain-type pressure transmitters. Pressure transmitter When the pressure signal acts on the sensor, the pressure sensor converts the pressure signal into an electrical signal, which is amplified by differential amplification and output amplifier, and finally converted by V / A voltage and current into the liquid level pressure with the measured medium (liquid). 4-20mA standard current output signal in linear correspondence. Sensors and transmitters play a pivotal role in the fields of instrumentation, instrumentation and industrial automation. Unlike sensors, in addition to being able to convert non-electrical power into measurable electrical power, the transmitter generally has a certain amplification effect.
How to choose a pressure transmitter: Determine the measurement medium, see the degree of corrosion of the measurement medium, and select the appropriate transmitter based on the degree of corrosion. Generally speaking, non-strong acids and alkalis can use transmitters with stainless steel as the isolation unit. Otherwise, you can only choose a special transmitter such as titanium alloy designed for corrosion protection. Secondly, it depends on the consistency and cleanness of the measuring medium. If it is very viscous (such as very slow flow), you need to select the transmission of the rigid isolation unit to determine the measurement range and measurement method. Generally, the actual measurement range should be considered when selecting the measurement range. Overvoltage measurement range. Select the range based on the maximum measurement range, and consider the size of the overvoltage measurement range. In addition, you need to choose the correct measurement method. If you are measuring differential pressure, you must choose a differential pressure transmitter to determine the accuracy range, compensate the temperature range, and use the temperature range according to the lowest accuracy you need to measure. Generally, products that are slightly higher than the required minimum accuracy are generally selected. At the same time, it is necessary to consider the long-term stability index so-called compensation temperature range, which is the temperature range of the measuring medium during normal operation. The use temperature range is the maximum temperature range that may occur during use. Generally, the pressure interface is slightly larger than the required temperature range to determine the pressure interface. Electrical interface, mechanical dimensions determine whether it is explosion-proof, environmental protection against electromagnetic interference, and environmental indicators