why the relay chatters & gives the output to the PLC CPU input & whole machine stops?

[munzir]

why the relay chatters & gives the output to the PLC CPU input & whole machine stops?

why the relay chatters & gives the output to the PLC CPU input & whole machine stops (trips) ?

the relay is 14 pin having AC 220 V coil voltage & output is 24 volts ......

the relay keeps energized when the machine is running & when its de-energized it gives 0 v dc output to the input of the PLC & machine stops ......

Basically the purpose of this relay is to generate the machine stop signal (when any of the two stop buttons are pressed or when any of the 9 emergency button is pressed) ......

all of the 9 emergency buttons are connected in series to each other and their NC (Normally closed) contact is used ......

when any of the emergency button is pressed or any stop button is presses (& the relay becomes de-energized & giving the 0 v dc output to the plc input) then there exist 10 V AC on the contacts of the relay ......



https://obrazki.elektroda.pl/13_1326120624.jpg
https://obrazki.elektroda.pl/19_1326120624.jpg


what's the problem ?

thanks

 

[ark5230]

Re: why the relay chatters & gives the output to the PLC CPU input & whole machine st

The reason why a relay chatters is the Basic Law of Inertia. When the relay changes its state (either from ON to OFF or OFF to ON), the spring loaded contact strip makes a physical movement and strikes against the other contact point. To every action there is an equal and opposite reaction (Newtons third law) this causes the contact strip bounce back. Depending on the inertia and the spring properties the amount of chatter and the resulting jitter could be different.

The remaining part of the issue I could not understand, you may please make it more clearer if you feel like

A Raoof Khan

 

[kak111]

Re: why the relay chatters & gives the output to the PLC CPU input & whole machine st

When i look at circuit drawning...
Stop contactor KA7 is connected between LA (220Vac) and N (Neutral).
Same voltage is in PLC points L1 - N.
Contactor stops the machine via PLC input I1.0
In normal RUN-state KA7 is always ON and I1.0 is always 0Vdc via KA7 contact.

1. Check voltage LA - N , should be stable 220Vac

2. Check voltage across KA7 coil , points J - N should be stable 220Vac

3. Check voltage across emergency buttons points LA - J , should be very near 0Vac.
- if voltage LA-J is not near 0Vac , problem is in emergency button circuit.
( Button switches or cables , loose connection or some additional resistance , break , etc.)

3. Chance contactor KA7.
- some times contactor like this , which is almost always energized,
coil plastic parts partially melt and contactor operation change to unreliable and unsure.
- coil partially shorted
- mechanical parts worn or damaged.

KAK

 

[munzir]

Re: why the relay chatters & gives the output to the PLC CPU input & whole machine st

i have already changed the relay (contactor) ... also changed the base of the relay (contactor)

---------- Post added at 22:04 ---------- Previous post was at 22:02 ----------

already checked the voltages at the emergency buttons ....... already changed the all of the 9 emergency buttons but the problem remains ..........

 

[kak111]

Re: why the relay chatters & gives the output to the PLC CPU input & whole machine st

Strange...
Is this relay chattering all the time or some periods.
What was the voltage measured across relay coil.
What is the exact type and manufacturer of this relay.

 

[ark5230]

Re: why the relay chatters & gives the output to the PLC CPU input & whole machine st

By any chance is that chattering related to some mechanical vibrations of machines or some rhythmic relationship with mechanical machines.

 

[munzir]

Re: why the relay chatters & gives the output to the PLC CPU input & whole machine st

Strange...
Is this relay chattering all the time or some periods.
What was the voltage measured across relay coil.
What is the exact type and manufacturer of this relay.

no not all the time ......... some periods ......
the strange thing is that when any of the emergency button is pressed or any of the stop button is pressed then there should be 0 V at the relay coil but there exist different voltages due to the different emergency buttons (located at different stations of the machine & at the other different locations ) being pressed .......

the emergency button and/or the stop push button at the farthest station (farthest distance) give 0 V and the second farthest one has 1V and the sequence & hence the voltage keeps increasing till the nearest one give 11 V AC output to the relay coil ..........

no vibrations ........

thanks


what do you mean by additional resistance & break ?

are you referring to the brake resistance & the brake of the inverters that are present in the machine's panel to control the 6 motors ..... ?

 

[munzir]

Re: why the relay chatters & gives the output to the PLC CPU input & whole machine st

Check voltage across emergency buttons points LA - J , should be very near 0Vac.
- if voltage LA-J is not near 0Vac , problem is in emergency button circuit.

Referring to your given statement above :

when the voltage should remain near 0 Vac across LA - J ? (when all of the 9 emergency switches are closed i.e. pressed or when they are open)

what sort of problem can it be that you're referring by stating that " problem is in emergency button circuit. " ?

thank$

 

[kak111]

Re: why the relay chatters & gives the output to the PLC CPU input & whole machine st

Here is picture , how to measure.....
Button switches and cables , loose connections and some increased resistance , breaks , etc.

 

[munzir]

Re: why the relay chatters & gives the output to the PLC CPU input & whole machine st

but how to lengthen the meter probes so that the meter probes may reach to the required potential points like LA to J ?

---------- Post added 13-01-12 at 00:01 ---------- Previous post was 12-01-12 at 23:59 ----------

switches are closed means pressed ???

 

[kak111]

Re: why the relay chatters & gives the output to the PLC CPU input & whole machine st

If measured voltage from LA to N is 220Vac and measured voltage from J to N is > 220Vac - 5%
there is no problem at that time.
But if measured voltage from J to N is < 220Vac - 10% there is problem in some switch , some cable or some screw connector.
Then you must find out by measuring between which connector points the voltage drop occurs.
i.e. you must measure every point to point voltage.
Every closed switch and cable should have voltage drop very near 0 volts , if there is found some higher drop for ex. 5V , its clear failure.
This mean every switch and every wire between switches must be measured individually.
Another way to do that is measure LA-SB1a and SB1a-SB1b and SB1b-SB2a and SB2b-SB3a and so on, until to point J.
You gonna need one long wire for lenghten one measuring cable.

switches are closed means pressed ???

In circuit drawning serially connected switches to stop relay are normally closed type, i.e. switch is open when pushed.

 

[munzir]

Re: why the relay chatters & gives the output to the PLC CPU input & whole machine st

there are some burnt contact in different connecting strips ...... don't you think that they might be the culprit .......?

also , most of them are neutral wire connections (connecting strip points burnt out majority of them are neutral wire connections)

thanks thanks very much

 

[kak111]

Re: why the relay chatters & gives the output to the PLC CPU input & whole machine st

there are some burnt contact in different connecting strips ...... don't you think that they might be the culprit .......?

Of course they might be...........
Remember that neutral is return wire for all 220Vac powered circuits.
They are just equally as important as 220Vac supply wires.
These circuits includes power supplies, relays, contactors, etc etc.
All of these terminals and connections must be inspected and repaired first.