Need Help

PB1 and PB2 are part of the manual mode (start/stop control), and 2posSS and LevelWS to control the MCR in automode.

2posSS is used to bypass the Manual Mode.

when the control is running in automode 2posSS(2 position Selector switch) is ON and PB1 and PB2 will not be used

Condition 1(Normal operation)
-when LevelSW is ON then MCR will ON. when LevelSW is OFF then MCR will OFF

Condition 2

When LevelSS and 2posSS(2 position selector switch is turn OFF very pass) is OFF at the sametime.
-MCR will is still ON

What is the best solution without rewiring the system in order that condition2 will not occur?

can I add resistor in shunt with 2posSS to absorb the energy in order not to turn MCR?


best regards,

Lovington Dela Crur

Not sure I understand what you're trying to do... Do you want to delay the MCR turning OFF so someone has a chance to flip the selector switch to manual? Why not just stick in off-delay timer?

beerchug

-Eric

Dear Lovington dela Crur,

it is impossible to determine what you want to do in your program, and so it is also impossible to give any advice.

The first thing you should do, is to tell a little what the problem or task is. What is the proces or the machine that you are trying to control.
Then you could tell something about how you have tried to solve the problem. What system have you chosen to solve the problem.
That will give us a chance to make meaningful recommendations to you.

Try Adding a 2posSS N.O. contact in series with the LevelSW N.O. This should let the 2posSS control the choice of devices. I too have no idea what you are wanting to do.

It looks like you are dealing with hardwired circuits, not PLC logic. However, the logic is still binary, with states being either on or off. The circuit you attached is electrically OK, and I'm not sure what you want to accomplish with the resistor. Normally you just use the contacts in series and parallel to accomplish your objective. Please let us know how your circuit is not doong what you want, and we can be of more help.

I think I understand, when the Selector switch is in Manual you dont want the Level switch to activate the MCR.

I have modified your drawing (as best I could) to show a possiblity of what I think you want.

In my drawing I am assuming that the 2 pos SS has a N.C. contact. When its off..ie in Manual mode then you would have to use PB 1 and PB 2 to turn on/off the MCR.

If the 2 pos SS is ON (using a normally open contact closed) then the Level switch will control the MCR on/off state.

This assumes this is a hardwired situation.
PERSONALLY I would look at wiring this differently. I would use the Stop/Start ckt to latch in the MCR then use a contact from it to allow the Level switch to do its action, that would give you a way to STOP the system when needed.

If I have correctly assessed what you are trying to do then this would offer the control you want but the safety of stopping the system at all times. The 2 pos SS using a N.O. contact when closed (in AUTO) would allow the level switch to perform its action automatically. Using a second N.O. contact (Manual) would allow you to control the same action the level switch does. You may also want to consider a 3 pos SS and have center position for an OFF condition.

I may be way off base so let us know.

Yes the elcetrical wiring I had presented is hardwired control.

THe operation is manual and auto.

During the manual mode:
-PB1 and PB2 is used to control the ON/OFF of MCR

During the Automode:
-LevelSW is used to control the MCR.

Electrically my hardwired control will work in normal condition.

During the automode when both LevelSW and 2posSS will turn OFF very pass at the same time the MCR will continously ON and this is
my problem. I want the MCR turn OFF when this situation occur.

Labintone

Have you had a look at Ron's modified drawing of your original?

That should solve your problem.

I would also recommend a 3 position switch, then you have auto, manual and off.

Paul

Yes The diagram of rsdoran will solve the problem. What Im trying to do is to solve the problem w/o doing the rewiring.


Paul,

Thats what im planning to replace the 2 position switch in to 3 position switch to have a Off condition.

hOW About putting a shunt resistor to a 2posSS. So that during the switching period the energy will absorb by the resistor. What do you think it will work or not.


Lovington

Labingtone

I am not sure what 'energy' you are trying to absorb using a shunt resistor, is it the back emf from the MCR as it drops out during switching? If that is the case then why not use a MOV (metal oxide varistor) across the coil of the MCR to disperse this energy.

Paul

PAUL,

Thanks.......


That is right I want to disperse the back EMF from the MCR during switching.

Lovington

PAUL,

Thanks.......


That is right I want to disperse the back EMF from the MCR during switching.

If the MCR rating is 5VA, 220V. How Im I going to size my MOV or how to size up an MOV.


Lovington

How Im I going to size my MOV or how to size up an MOV

Click to expand...

That is a good question, I am sure that there is a math way of doing this but, when we buy our MOV's we go by the RMS of the supply voltage and then pick the biggest clamping voltage possible for that one.

Have a look at this site RS.COM MOVs that might help you

Paul