PLC communication port is damaged, the PLC input capacitance between lines cause misoperation -

by:Coolmay     2020-07-07
PLC communication port 1 damage case

we have a project, PLC port burn out. PLC communication line through the slip ring raises. Given a few days ago just rained, doubt is slip ring caused by the water PLC communication line short circuit, and seize the PLC port.

shaking table was used to measure the communication line ( Line ends dangling) , found that the communication between the line resistance, normal should be infinite, and measurement, the resistance between the 5 m to 10 m. Thus concluded that PLC port burn was caused by slip ring into the water, normal after replacement slip ring.

2 to avoid multiple calls to the same subroutine

in the program, multiple calls to the same subroutine, there is no mistake in grammar, but we will try to avoid this practice, especially in a with a formal parameter. The following through the example to illustrate.

the following shown in figure 1, 13 and 14 are called network protection, subroutines, at this time, the operation of the network protection, 14 calls a subroutine is shown in figure 2. We note that the network parameter # 14 calls numerical protection ( 13, 1169, network parameter value when calling the subroutine) Is not a network protection, 14 call subroutine to numerical ( Should be 481) 。 In this way, can cause we don't want the results.

3 PLC controller input capacitance between lines cause misoperation

between different wires in the cable capacitance, qualified cable can limit the capacity value within a certain range. Is qualified cable, when the cable length exceeds a certain length, the capacitance between each wire capacitance value will be more than the required value, when using this cable for PLC input line capacitance is likely to cause the malfunction of PLC, there will be many don't understand. Mainly for: clearly wiring is correct, no PLC should have some input, and should not have had, namely PLC input from interfering with each other.

recently, when debugging a PLC system, is a kind of phenomenon appeared. MIC sensor is not action, or action, another sensor ( 飞) Actions affect the MIC sensor, i. e. , MIC gesture, FLY a movement sensor, MIC they became not action. Namely: sensor actions affect each other, doubt is the cable quality is bad, line capacitance caused by unsuitable. The MIC sensor received directly to the PLC, do not use the cable, after all the action is normal.

eliminate line capacitance effects:

1) Use the cable core cable twisted together;

( 2) As far as possible to shorten the length of the cable used.

( 3) Separate the mutual interference of input cable to use;

( 4) Use the shielded cable.

4 reasonable PLC programming to eliminate wrong operation

1) Eliminate the fingers vibrate

using differential commands DIFU ( 13) To retrieve the button into electrical signals, delay in an execution cycle PLC execute only once, so as to avoid the wrong operation.

( 2) Unconscious action (1) to optimize the display, the use of different indicator light to show the different kinds of working state: flat - running state, the high frequency flash ( 1) 1 SEC - test condition, low frequency flash ( 3 seconds flash 1 time) - step by step. (2) input signal interlocking

5 inverter overvoltage handling a case of a

reduce given the operation of the motor speed, motor into renewable power brake, the motor feedback energy to frequency converter is also high, the energy stored in the filter capacitor, the capacitor on the voltage rise, and quickly achieve the dc overvoltage protection setting value and make the inverter tripping.

processing methods: external add inverter braking resistance measures, with the resistance will be feedback to the side of the dc motors renewable energy consume.

6 converter overcurrent handling a case of a

we use yaskawa inverter with 120 small motor, occurs when one of the small motor over-current failure, the inverter will flow fault alarm, lead to frequency converter brake, which can lead to other normal small motor also stop working, and this is what we don't expect.

processing method: isolation transformer in inverter output side with 1:1, when one or a few small motor over-current fault, fault current transformer dc, rather than the impact frequency converter, thus preventing the tripping of the inverter. After the experiment, the work is good, haven't happened before also stop the normal motor fault.


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