Xue Fu Lian (Shenyang Liaocheng County Chemical Plant, 110200) CLC: TP273 Document code: A 1 Analysis and processing of oscillation causes during the operation of the electric actuator The control system put into automatic operation often encountered the appearance of the actuator This oscillation phenomenon, the oscillation frequency is higher. Due to the existence of this oscillation phenomenon, can easily lead to the magnetic amplifier failure, in addition, the electric actuator often in oscillation state, seriously affecting the service life of institutions. Therefore, in the regulation of the system should eliminate this oscillation, in order to ensure the regulation of the normal operation of the system. There are many reasons for the valve actuator to oscillate. Now we combine the experience of design, installation, commissioning and operation to explain the cause of actuator oscillation and how to eliminate it. (1) electric, actuator valve feedback small loop oscillation, the main reasons for oscillation are the following two aspects. a) As the dead zone of magnetic amplifier △ g is too small, the magnetic amplifier is too sensitive, so that the actuator small loop can not be stable and produce oscillation. b) When the actuator loses its braking effect and causes idling, it will also cause the actuator to oscillate in the small circuit. In view of the above causes the actuator oscillation, the magnetic amplifier is not sensitive △ g is too small to cause oscillation, according to the experience of operation, the insensitive area △ g of the magnetic amplifier is adjusted to ± 120-140 μ A to eliminate the small loop oscillation . For the implementing agencies to lose their brakes should be found out the reasons for the body to lose brake to be excluded. (2) Oscillation of the actuator due to signal fluctuations. Can be designed in the system, in the loop to join the damper link, but also in the pipeline plus mechanical filter buffer device. Mechanical damping method to reduce the transmitter output signal fluctuations, and thus eliminate the body oscillation. (3) due to improper tuning of the system parameters caused by system oscillation, the actuator oscillation. Regulator parameter tuning is not suitable, will cause the system to produce varying degrees of oscillation. For a single sleep adjustment system, the proportional band is too small, the integration time is too short, the differential time and differential gain is too large may produce system oscillations. For multi-loop systems and single-loop systems have common problems, but also the existence of the circuit of the production of mutual influence, due to improper parameter settings produce resonance between the circuits. For the above reasons, the actuator oscillation may be selected reasonably when the system is tuning, so that the loop should maintain the desired stability margin. (4) As the regulating valve flow characteristics are too steep or the valve is operating at a small opening, causing the actuator to overshoot and cause the actuator to oscillate. When the flow characteristics of the control valve is too steep, only a small deviation of the gas station will result in more changes of the medium to be adjusted, which often causes the adjustment too far and the system will oscillate. As the characteristics of regulating valve by the process conditions, more difficult to modify, you can adjust the proportional increase with an appropriate to improve the quality of regulation. (5) Clearances and clearances due to the linkage of the actuator to the linkage and the regulator gate. All couplings should be three-precision manufacturing. Oscillation of the actuator is a kind of common fault phenomenon in operation, which has a direct impact on the quality of regulation. There are many internal reasons for it. When analyzing and queuing the cause of the fault, it is necessary to analyze the cause of the fault from many aspects of system configuration, installation and debugging, Eliminate. 2 Vortex flowmeter to solve the anti-electromagnetic interference measures Vortex flow planning work At present, the more advanced flowmeter meter better application in recent years, the flowmeter measurement accuracy, operation *, easy to install. However, the use of vortex flowmeter in the field, there is the problem of interference, the use of our plant point of view, electromagnetic interference is the main. (1) low frequency electromagnetic interference on the vortex flowmeter, low frequency electromagnetic interference, that is, the use of the field, from the AC power supply (220V, 50Hz), because the installation, in order to track norms, often through the cable tray or protective tube, It is possible for the AC power to be routed in parallel with the signal line and the interfering signal will be coupled to the signal output line. From the power line to the signal distribution capacitor C, the promulgation of capacitive coupling caused by the interference voltage to send pictures to the phone, the picture below: From the above equation or know: the signal line and the power line closer to the distribution capacitance C in , The greater the interference voltage; the higher the pre-amplifier input impedance Rsr of the vortex flowmeter, the greater the interference voltage, the interference pulse signal may be generated so that the secondary table measurement is inaccurate. Thus, by increasing the distance between the power line and the signal line, reducing the distribution of people and a reasonable choice of signal line grounding point, you can avoid interference voltage on the vortex flowmeter. (2) anti-electromagnetic interference measures a) the use of shielded cable output signal; b) try to avoid laying AC power supply (220V, 50Hz) c) site installation conditions are not good, really clear bitter, signal line shielding must be * Grounding; d) the signal line with metal protection fixed to reduce vibration and shock, to avoid electrostatic interference; e) vortex flowmeter transmitter input and output remain dry and clean; f) signal lines and vortex Flow reading newspaper transmitter away from high-power motors, transformers and other power equipment. For example, in our factory there is a vortex flowmeter secondary instrument installed on the electric plate, the plate has high and low limit alarm bells, alarm when the second instrument count has a great impact, making it jump. Analysis of the reasons is that the secondary instrument power supply part of the first interference signal, the lower DC output, resulting in interference pump and the counter part of the interference pulse signal, making it the first chaos phenomenon. We are in the secondary part of the power supply plus a filter circuit to eliminate electromagnetic interference, so that the secondary table count to ensure accurate measurement.