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Pressure transmitter is one of the most commonly used sensors in industrial practice, which is widely used in various industrial self-control environments, involving water conservancy and hydropower, railroad transportation, intelligent buildings, production automation, aerospace, military, petrochemical, oil wells, electric power, ships, machine tools, pipelines and many other industries.
Pressure transmitter is a pressure into a pneumatic signal or electric signal for control and remote transmission of the device.
It can be felt by the pressure measuring element sensor gas, liquid and other physical pressure parameters into a standard electrical signal (such as 4 ~ 20mADC, etc.) to supply the indication of the alarm, recorder, regulator and other secondary instruments for measurement, indication and process regulation.
Pressure types are mainly gauge pressure, absolute pressure, differential pressure, etc. Gauge pressure refers to the atmosphere as the reference, less than or greater than the atmospheric pressure; absolute pressure refers to the absolute pressure zero as the reference, higher than the absolute pressure; differential pressure refers to the difference between the two pressures.
In general, according to the actual measurement pressure is 80% of the measurement range selected, to consider the maximum pressure of the system. In general, the maximum value of the pressure transmitter pressure range should reach 1.5 times the maximum pressure value of the system. Some water pressure and process control, there are pressure spikes or continuous pulses. These spikes can reach 5 or even 10 times the "maximum" pressure and can cause damage to the transmitter. Continuous high pressure pulses, near or above the maximum pressure rating of the transmitter, can shorten the life of the transmitter. However, increasing the transmitter pressure rating will sacrifice the resolution of the transmitter. A buffer can be used in the system to attenuate spikes, which can reduce the response of the transducer.
Pressure transmitters are generally designed to withstand a maximum pressure over 200 million cycles without degrading performance. A compromise can be found between system performance and transmitter life when selecting a transmitter.
According to the different measurement media, can be divided into dry gas, gas liquid, strong corrosive liquid, viscous liquid, high temperature gas liquid, etc., according to the correct selection of different media, in order to help extend the life of the transmitter.
The maximum overload of the system should be less than the overload protection limit of the transmitter, otherwise it will affect the life of the transmitter or even damage the transmitter. Usually the safety overload pressure of the pressure transmitter is two times the full scale.
The measurement error of the transmitter is divided according to the accuracy level, different accuracy corresponds to different basic error limits (expressed as a percentage of the full-scale output). In practice, according to the measurement error control requirements and in line with the use of economic principles to choose.
The temperature of the measurement medium should be in the working temperature range of the transmitter, such as over-temperature use, will produce a large measurement error and affect the life of the transmitter; in the production process of pressure transmitters, the temperature impact will be measured and compensated to ensure that the measurement error generated by the temperature impact is within the range of accuracy level requirements. In the higher temperature occasions, you can consider choosing high temperature type pressure transmitter or take the installation of condenser tubes, radiators and other auxiliary cooling measures.
In some measurement occasions, the measurement medium is corrosive, when you need to choose a material compatible with the measurement medium or special process to ensure that the transmitter is not damaged.
Usually the threaded connection (M20×1.5) of the direct mount pressure transmitter is the standard interface form.
Usually the pressure transmitter is powered by DC power supply, providing a variety of output signal options, including 4-20mA, 1-5V, etc., can be 485 digital output.
Whether there is vibration and electromagnetic interference, etc., the relevant information should be provided during the selection so that the corresponding treatment can be taken. In the selection, other such as electrical connections can also be considered according to the specific circumstances.
If the size of the mounting hole is not appropriate, the sensor in the installation process, its threaded part is susceptible to wear. This will not only affect the sealing performance of the equipment, but also make the pressure sensor can not fully play a role, and may even produce safety hazards. Only a suitable mounting hole can avoid the wear of the thread (thread industry standard 1/2-20 UNF 2B), and usually a mounting hole measuring instrument can be used to test the mounting hole to make appropriate adjustments.
It is important to keep the mounting holes clean and prevent melt clogging to ensure proper operation of the equipment. Before the extruder is cleaned, all pressure sensors should be removed from the barrel to avoid damage. During sensor removal, melt can flow into the mounting holes and harden, and if this residual melt is not removed, it can cause damage to the top of the sensor when it is re-installed. The cleaning kit can remove these melt residues. However, repeated cleaning processes may deepen the damage to the sensor caused by the mounting holes. If this happens, steps should be taken to elevate the sensor in the mounting hole.
If the sensor is installed too far back in the line, a stagnant zone of molten material may be created between the sensor and the screw stroke, where the melt may degrade and the pressure signal may be distorted; if the sensor is too deep in the barrel, the screw may touch the top of the sensor during rotation, causing it to be damaged. If the sensor is too deep into the barrel, the screw may touch the top of the sensor during rotation and cause damage. Generally, the sensor can be located on the barrel in front of the screen, in front of or behind the melt pump, or in the mold.
Although the sensor circuitry is designed to withstand the harsh extrusion process environment, most sensors are not absolutely waterproof and are not conducive to proper operation in wet conditions. Therefore, it is necessary to ensure that water in the water cooling unit of the extruder barrel does not leak, otherwise it will adversely affect the sensor. If the sensor has to be exposed to water or humid environment, choose a special sensor with extreme waterproofness.
Before cleaning the extruder barrel with a wire brush or special compound, all sensors should be disassembled. Because both cleaning methods may cause damage to the vibration film of the sensor. When the barrel is heated, the sensors should also be disassembled and their tops wiped with a soft cloth that will not cause abrasion, and the holes in the sensors need to be cleaned with a clean drill and guide.
