What are the faults and cause analysis of electric regulating valve accessories?

The accessories of the electric control valve include pre-magnetic amplifier, control valve, etc. Here we mainly talk about the correct use and maintenance of the servo amplifier of the electric control valve. Daily professional maintenance can not only improve the reliability of the process control, but also increase the service life of the electric control valve. The following is a detailed introduction to the causes and solutions of the faults by Ningbo Jiaerling Pneumatic Machinery Co., Ltd.:

If the preamplifier of the electric regulating valve is not working properly, there may be the following four situations for each part:
(1) Pre-magnetic amplifier
①When there is no signal input, the output of the double-beat magnetic amplifier can be adjusted to zero through the potentiometer W101. If zero adjustment is not possible, it may be:
A. Transformer W101 is desoldered or damaged.
B. The resistors R110 and R111 and the electrolytic capacitors C101 and C102 are soldered or desoldered.
C. Diodes D105~D108 are soldered or damaged.
D. The offset current is abnormal.
E. The AC winding is asymmetrical.
②There is input signal, but no output or output asymmetry may be:
A. The secondary terminal voltage of the transformer B301 for the AC winding current is asymmetrical.
B. The resistance values ​​of the resistors R110 and R111 have changed, and the electrolytic capacitors C110 and C111 are damaged.
C. The AC excitation winding is short-circuited.
D. Some of the diodes D105~D108 are damaged or soldered.
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(2) When the trigger has input, one side of the trigger should have a pulse signal on the oscilloscope screen, and if the polarity of the input signal is changed, the other side of the trigger will have a pulse signal. The number and amplitude of trigger pulses in the two groups should be basically the same. Otherwise, there are the following situations.
① There is no input signal (the pre-magnetic amplifier is in normal working state), and there is a trigger pulse at the output, which may be:
A. The triode on the side of the trigger pulse output is damaged, or the c and e poles are soldered.
B. The resistance values ​​of resistors R204, R205, R208 and R209 have changed.
②There is an input signal, but there is no trigger pulse at the output, which may be:
A. The triode and single junction tube on the side without output pulse are damaged.
B. The primary or secondary of the pulse transformer on the side with no output pulse is open or short-circuited.
C. The diode (D207 or D208) on the side without output pulse is short-circuited.
③The abnormal output trigger pulse has the following phenomena:
A. When there is no signal, the two sets of triggers have pulse output. After adding the signal, they are all normal. It may be that the electrolytic capacitor C202 or C203 is soldered.
B. The output on both sides of the trigger is normal at the beginning. After working for a period of time, the output pulse gradually disappears. There may be a problem with the single-junction tube.
C. Positive and negative pulses appear in the output, it may be that diodes D207 and D208 are broken down or soldered.

(3) After the above inspection and maintenance, the servo amplifier should be able to work normally if the control loop is fault-free. Otherwise, there are two situations:
①When there is no input signal, if there is an output voltage (the voltage is close to 220VAC), it may be:
A. The thyristor SCR1 and SCR2 are damaged.
B. The capacitors C301 and C302 are broken down.
②When there is an input signal, if there is no output signal or the output voltage is low, it may be:
A. Diodes D301~D308 are broken down.
B. The thyristor SCR1 and SCR2 are damaged.

When the servo amplifier of the electric control valve is in normal working state, there may be the following three situations:
(1) When there is no input signal, there should be no output voltage.
(2) The open-loop dead-zone current is ≤160μA (type II is 100μA).
(3) When the input signal is greater than 240μA (type II is 150μA), the output load voltage is ?205~220V?AC.
(4) The output voltage is basically symmetrical.