What can the transmitter do?
In industrial production, the measurement element will be pressure, temperature, flow, level and other parameters detected, the need for the transmitter will be measured components of the unified signal conversion to a standard signal source (such as 4 ~ 20mA DC power supply), sent to the display Instrumentation or adjustment of the instrument for display, recording or adjustment. Therefore, the transmitter is a conversion medium, it is a medium.
What are the strong points of transmitters?
As the regulator is generally in the relatively distant control room, the transmitter becomes a signal generation and transmission line drive the two functions of the complex, as the entire control device in the heart, with it, it makes control End and measuring end linked to form a complete set of control systems.
What is the category of the transmitter?
Some transmitters in the measurement and transmission unit to be integrated (such as pressure transmitter), and some transmitters are only transmission function (such as temperature transmitter).
The transmitter is powered by a pneumatic transmitter and an electric transmitter.
Among them, the industrial production process is the most commonly used differential pressure transmitter and temperature transmitter.
Differential Pressure Transmitter Common Types and Selection Principles
The differential pressure transmitter is used to convert the measured parameters such as differential pressure, flow rate, liquid level and so on into a unified signal standard and transmit the unified signal to the indicator, record the instrument or adjuster so that the measured parameters are displayed on the screen.
The main types are: force balance type electric differential pressure transmitter, capacitive differential pressure transmitter
Differential pressure transmitter model is not specified, each manufacturer has its own selection table. Differential pressure transmitter on the selection of the main basis: to test the nature of the media subject to control, to save money, easy to install and maintain as a reference. If the measured medium for high viscosity easily crystalline strong erosion of the occasion, must use isolation type transmitter.
Differential pressure transmitter in the selection of the media to consider the media on the membrane metal erosion, must choose a good membrane material, the transmitter membrane material has ordinary stainless steel, 304 stainless steel, 316L stainless steel, tantalum membrane material Wait.
Differential pressure transmitter in the selection to consider the temperature of the measured medium, if the temperature is generally high 200 ℃ ~ 400 ℃, to use high temperature type, or silicone oil will produce vaporization expansion, so that measurement is not allowed.
Differential pressure transmitter in the selection of equipment to consider the level of work pressure, the transmitter pressure level must be consistent with the application. From the choice of transmitter measurement range, the general transmitter has a range of adjustable range, it is best to use the range range in its range of 1/4 to 3/4, so that accuracy will be guaranteed, For micro differential pressure transmitter is more important. In practice, some applications (liquid level measurement) need to measure the transmission range of the transmitter, according to the location of the site to calculate the measurement range and migration, migration and positive migration of the points.
The same time as
Differential pressure transmitter in use should pay attention to the nine questions:
1. When measuring gas pressure, the suction port should be opened at the top of the process piping and the transmitter should be installed in the upper part of the process piping so that the accumulated liquid is easily injected into the process piping.
2, the pressure pipe should be installed in a small place where the temperature fluctuations;
3, to prevent the transmitter and corrosive or overheated media contact;
4, to prevent the sediment in the catheter deposition;
5, the measurement of liquid pressure, the pressure should be opened in the flow side of the pipeline to avoid sedimentation slag.
6, the measurement of steam or other high-temperature medium, the need to take a buffer tube (coil) and other condenser, should not make the transmitter operating temperature exceeds the limit.
7, winter freezing occurs, according to the outdoor transmitter must take anti-freeze measures to avoid the pressure inside the mouth of the liquid volume due to ice expansion, resulting in sensor damage.
8, the measurement of liquid pressure, the transmitter should be installed to avoid the location of the impact of liquid (water hammer phenomenon), so as to avoid damage to the sensor overpressure.
9, the wiring, the cable through the waterproof connector (accessories) or around the tube and tighten the sealing nut, to prevent rain and other water leakage through the cable into the transmitter housing.
Explosion-proof identification of process control instruments
Many of the petrochemical industry in the production of flammable and explosive gases, dust, etc., installed in such occasions, if the instrument sparks, it is easy to cause burning or explosion, resulting in huge losses of personnel and property. So the instrument must have a safe spark explosion-proof performance. Explosion-proof instruments are explosion-proof inspection certificate number and explosion-proof type, grade and other signs of the nameplate.
The typical logo on the nameplate explosion proof mark is divided into four sections: Ex, A, B, C.
Ex is the explosion-proof instrument; A paragraph filled with explosion-proof type, such as d, ia, ib, etc., B for the explosion-proof instrument class and set, such as I, IIA, IIB, IIC; C for the explosion-proof instrument surface temperature Group, such as T1 ~ T6. For example, ExdiaIICT6 indicates both flameproof and intrinsically safe functions, and can be used in the IIC grade T6 group at the following levels.
Fault Analysis of Differential Pressure Transmitter
Transmitters in the measurement process, often there will be some failures, fault analysis and processing of the timely analysis of the ongoing production is essential. Based on our experience in daily maintenance, we summarize some of the analytical methods and analysis process.
Transmitter measurement process, often there will be some failures, failure to determine the timely analysis and processing, is carried out for the production is essential. Our daily maintenance experience, summed up a number of decision analysis methods and analysis process.
Investigation method Review the fire before the fire, smoke, smell, power changes, lightning, wet, misuse, misuse.
2. Intuitive method. Observe the circuit external damage, pressure pipe leakage, loop overheating, power switch status.
3. Detection method.
Open circuit detection: the fault will be part of it part of the separation to see whether the fault is gone, disappear, then determine the fault, or can be the next step to find, such as: intelligent differential pressure transmitter can not normally Hart remote communication, power from The instrument on the body off, with the scene plus the power method for the sensor power to communicate to see if the cable is superimposed about 2kHz electromagnetic signal and interference communication.
Short circuit detection: to ensure that the security situation, the relevant part of the circuit directly shorted, such as: poor transmitter output value is too small, can be off the pressure pipe, from a pressure valve directly to the differential pressure signal directly lead to poor Pressure sensor on both sides, observe the transmitter output to determine the pressure pipe blocking, leakage connectivity.
Replace the test: the suspected part of the replacement, to determine the fault location. Such as: suspected transmitter circuit board failure, can be temporarily replaced to determine the cause.
Segment detection: the measurement circuit is divided into several parts, such as: power supply, signal output, signal transmission, signal detection, by sub-part of the inspection, from simple to complex, from the table and the narrow range to find the fault location.
Temperature transmitter with a variety of thermocouple or thermal resistance used in conjunction with the measured temperature can be linearly converted to 0 ~ 10mA or 4 ~ 20mADC current signal to facilitate the display, recording and adjustment unit with the work.
In accordance with the different types of temperature sensors used, the temperature transmitter is divided into three types: DC ho power transmitter, resistor body temperature transmitter, thermocouple temperature transmitter.
The advantage is the use of low-drift, high-gain linear integrated circuits, improve the reliability of the instrument, stability and technical performance. At the same time as a result of the linear circuit, to keep the transmitter output signal and the measured temperature signal to maintain a linear relationship. And the line used in the safety spark explosion-proof measures, can be used in dangerous places in the temperature measurement.