The purpose of adjustment and automatic control. 1 Structure and working principle of pneumatic differential pressure transmitter The pneumatic differential pressure transmitter is divided into two types: single-variable rod type and double-variable rod type. Single-variable rod type is widely used in ships. This paper uses single-variable rod type. Pneumatic differential pressure transmitter is introduced, 1 is the structure of the differential pressure transmitter, and 2 is the working principle box of the transmitter. 1.1 Measuring the composition of the membrane cartridge 3, which is composed of a housing diaphragm variable rod and a sealing device fixed in the middle of the diaphragm by a base on the housing, the diaphragm is filled with silicone oil, because the silicone oil is a low freezing point and An organosilicon compound having a small expansion coefficient, which acts as a medium for pressure transmission in the diaphragm to form a damping, thereby avoiding a oscillating change of the diaphragm under pressure. When installation or operation error occurs, the pressure on the low pressure side is higher than the pressure on the high pressure side. Due to the damping of the silicone oil, the diaphragm is slowly displaced. When the protective seal is moved into contact with the base, the silicone oil on both sides is closed. The diaphragm is no longer displaced, preventing excessive displacement of the diaphragm. The diaphragm divides the closed chamber into two chambers, a low pressure chamber and a high pressure chamber, and the diaphragm is connected to the variable rod. When there is a pressure difference between the high and low pressure chambers, the diaphragm drives the variable rod to move to drive the differential mechanism. Pneumatic work technology 骣 1.2 differential mechanism differential mechanism is used by the variable rod fulcrum connected to the diaphragm, the deformation of the variable rod to move the fulcrum left and right, which causes the gap between the nozzle baffle and the nozzle to change, At the same time, the variable rod moves in the opposite direction with the fulcrum B under the action of the feedback mechanism. 1.3 Back Pressure Detection Mechanism The nozzle of the differential pressure transmitter is sprayed with a constant air flow. When the gap between the baffle and the nozzle changes, the nozzle ejects a constant amount of back pressure, and the back pressure signal is power. The input signal to the amplifier is also the key to the differential pressure transmitter. 1.4 The main task of the pneumatic power amplifier amplifier is to accept the back pressure signal and adjust the opening of the internal valve of the amplifier according to the strength of the back pressure signal, change the control air pressure of the control pilot spool, and make the pilot spool proportionally controlled to move. The valve inside the amplifier outputs a proportional air pressure to the input signal. This proportional constant is the amplification factor of the pneumatic power amplifier. 1.5 The feedback mechanism is sent from the air pressure portion of the amplifier output to the feedback mechanism, and its telescopic force causes the variable rod to move with the fulcrum 3, and the direction of the torque is opposite to the torque direction of the diaphragm driving the variable rod, thereby forming a negative feedback. The purpose is to allow the variable rod to form a force balance under different fulcrums, so that the nozzle and the baffle gap are fixed, that is, a fixed output air pressure proportional to the fixed differential pressure input. When disassembling and repairing the bellows, it is necessary to keep the end faces in good contact without being damaged or deformed. Otherwise, the torque generated by the bellows will change, resulting in a decrease in measurement accuracy. 1.6 Differential pressure transmitter input and output relationship The rated differential pressure of the pneumatic differential pressure transmitter is 1. 481 requires air supply pressure fluctuations, small pressure is stable and clean and dry to avoid damage to the amplifier or block the nozzle. When the pressure difference measured by the bellows changes at a minimum or maximum, that is, when the gap between the nozzle baffle and the nozzle reaches a maximum or minimum, the gas content of the output changes. According to this characteristic, we can determine the air pressure value and set value to be controlled by the actuator by measuring the range of variation of the object, and achieve the optimal setting of self-control and automatic adjustment. 2 differential pressure transmitter repair and adjustment of water level changes, or output pressure instability or output pressure value and measured error is very large, which will directly affect the normal use of the boiler and the safety of the boiler, how to introduce It is repaired and adjusted. 2.1 Inspection of Differential Pressure Transmitter When the output pressure of the differential pressure transmitter does not change with the water level, the differential pressure transmitter should be judged first or fore. 2.1.1 Check if the air source and nozzle are blocked, push the nozzle baffle with your finger to make it close to the nozzle to see if the output air pressure is 1.218, and then move the nozzle baffle away from the nozzle. The output pressure is 0.2 ft.8, 712. If the output pressure If the change is normal, the nozzle and power amplifier work well; when the output air pressure does not change, the amplifier and nozzle mechanism should be disassembled to remove dirt and eliminate air leakage. 2.1.2 Check the bellows mechanism, close the actual water level and the reference water level shut-off valve to open the balance valve, so that the pressure difference between the high and low pressure chambers is zero, artificially create a high water level, then the output air pressure should be 1.2 feet 812, then Close the actual water level shut-off valve and balancing valve, open the reference water level shut-off valve and open the venting cock of the actual water level side membrane box to maximize the pressure difference between the high and low pressure chambers, that is, artificially create the lowest water level. At this time, the output air pressure should be 0.28. If the output pressure changes normally, the bellows works normally, and vice versa. 2.1.3 When disassembling the bellows, care must be taken to connect the oil seal and the variable rod. Do not allow the sharp layer to leak the silicone oil inside the diaphragm. When the silicone oil in the diaphragm leaks more or leaks light, it must be filled with silicone oil, otherwise the bellows will not be used. 2.1.4 When the output air pressure is unstable or the error is too large, the mechanism should be inspected and adjusted. The pressure reducing valve input to the air source is working normally. Clean the inside of the pressure reducing valve and the filter to reduce the air resistance of the pressure reducing valve. Set the pressure to . 4 feet, 2. 2.1.5 Check whether the amplifier and nozzle mechanism have dirty plugging and air leakage. In most cases, the nozzle is dirty and the connecting hose is aging and leaking. 2.1.6 Check whether the lock nut of the feedback mechanism of the transmitter is loose or not, and the force area of ​​the zero spring and the bellows changes. Check whether the bellows leaks. If the air leaks, use the same end area of ​​the same model. Corrugated pipe replacement. 2.1.7 When the corresponding component is replaced or the above components are working properly, the differential pressure transmitter should be adjusted. 2.2 Adjustment of pneumatic differential pressure transmitter 2.2.1 Adjustment of zero position and range When updating the differential pressure transmitter or replacing the internal components, it should be adjusted for zero and span. The so-called zero adjustment is when the water level of the boiler At the lowest time, when the measured differential pressure is maximum, the output air pressure should be 0.2 ft8. If it is not equal to this value, the zero screw should be adjusted so that the output air pressure is equal to this value. The so-called range adjustment is when the boiler water level is at the highest water level, that is, when the measured pressure difference is zero, the output air pressure is 1. The specific step of 2 feet 8 is to first determine the measurement range of the water level, that is, the height difference between the lowest water level and the highest water level, the unit is 4, after the range is determined, the range pointer 3 is fixed at the position, and the above method is used to artificially manufacture the lowest water level signal, and the zero position is adjusted. Screw and baffle adjust the wire to the output pressure of 0.2Kgcm2. Then gradually increase the actual water level to the output pressure of 1.0KgCm2, and observe whether the actual water level is a normal high water level. If it is lower than the normal high water level, the range is less than the measurement. For the range, the range pointer 8 should be moved up and re-zeroed. If the range is still not suitable, repeat the above operation again by changing the position of the range fulcrum. Repeat the above adjustments until the zero position and the range are adjusted. At this time, the output pressure of the lowest water level and the normal high water level is 0.2, 0, 2, and the output pressure of the lowest water level and the highest water level is 28. 2.2.2 Migration adjustment The so-called migration is to transfer the starting point of the transmitter from zero to a certain value according to actual needs. The starting point and the ending point of the range are changed but the range is unchanged. Most of this happens when replacing a new differential pressure transmitter, especially the differential pressure transmitter of the alternative model. The output air pressure is exactly the opposite of the actual measurement result. When the low water level is output, l.OKgCrn2, when the high water level is output, 0.2 Han. This will cause confusion in the control and protection devices and the water level will be exactly the opposite. The adjustment method is to adjust the migration spring, that is, the baffle adjustment screw, at the lowest water level, and pull the baffle away from the nozzle so that the output air pressure is 2 ft 2 , and then gradually decrease with the negative value of the upper pressure difference of the water level, relying on the migration spring The tension causes the baffle to gradually approach the nozzle, and the output air pressure rises continuously until the normal high water level, the output air pressure is 1.08, 2, and this migration is called negative migration. Practice has proved that migration adjustment can increase the measurement sensitivity of differential pressure transmitters. 3 Differential Pressure Transmitter Maintenance and Maintenance Install the differential pressure transmitter to make the variable rod vertical installation. If the vibration is large, the vibration reduction measures must be taken. It is necessary to keep the air supply pressure sufficient and clean, and keep the work space air dry. Use a pressure reducing valve with less air resistance to provide 1.4Kgcrn1 working air for the differential pressure transmitter and regularly clean the filter screen of the pressure reducing valve. Periodically clean the nozzle and amplifier nozzles using the cleaning button on the unit. After the disintegration cleaning, it should be blown dry with a hair dryer, and sealed according to the mark to ensure the sealing. Regular inspection, each lock nut in the device to prevent the drop of measurement accuracy and the drift of the zero position. Regular inspection, each stop valve and balancing valve to prevent the internal leakage of the balancing valve from affecting the measurement accuracy. Periodically check the input output line of the differential pressure transmitter to eliminate air leakage. Kitchen Floor Drain,Stainless Steel Kitchen Floor Drain,Hidden Square Gold Shower Floor Drain,Round Black Shower Floor Drain Kaiping City Jinqiang Hardware Products Co.,Ltd , https://www.jqfloordrain.com
Analysis of pneumatic differential pressure transmitter