2 x DO VS 1 x DO

Indiaum

Member
I
Join Date
Jan 2010
Location
Brasil, Minas Gerais
Posts
54
Hi guys,

I barely know about electrical theory, so i wish to know your opinion on the subject. Lets say we have a engine, we want to turn it on and turn it off from the PLC. It is better to use one discrete output to turn it on and one discrete output to turn it off and let the physical circuit hold the engine running, or use one discrete output to turn it on, when its state is 1 and turn it off when its state is 0?

Thank you for your attention and sorry about my english.
 
Last edited:
Not really if you only use one. If you used a do to shut down then if the signal ever faild the equipment would run in a uncontroled state maybe.
 
their arguments on the use of two DOs, is something about lowering the stress on the PLC, since it will not need to keep its DO energized all the time....lowering the risk of an overload too....makes sense?
 
When a motor drive is standalone and there is no other control hardware except the start/stop contacts, then:
- Use 2-wire control if using 2-position selector switch (Run/Stop) with single contact.
- Use 3-wire control if using separate Start/Stop buttons or 3-position selector switch (Start/Neutral/Stop) with 2 contacts.

When a motor drive is controlled by a host controller, I see no reason to use 3-wire control, as the start/stop logic should be executed by the controller.
 
Indiaum said:
their arguments on the use of two DOs, is something about lowering the stress on the PLC, since it will not need to keep its DO energized all the time....lowering the risk of an overload too....makes sense?
Click to expand...

This makes no actual sense to me. How is the controller stressed again?
 
Indiaum said:
Hi guys,

I barely know about electrical theory, so i wish to know your opinion on the subject. Lets say we have a engine, we want to turn it on and turn it off from the PLC. It is better to use one discrete output to turn it on and one discrete output to turn it off and let the physical circuit hold the engine running, or use one discrete output to turn it on, when its state is 1 and turn it off when its state is 0?

Thank you for your attention and sorry about my english.
Click to expand...
al depends on what you are doing.
If you were starting and stopping a diesel engine, you have no choice but to use two outputs.
Also
If you need certain functions to happen before/after a stop/start, Brake release, clutch disable for example.
However, If you are starting/stopping some type of motor it depends on what you need.
I suggest ther is no normal functional reason why you would not use a single output.
Pro's and Con's
=
Ask yourself "what happens If?"
power to PLC drops out
Output fails to function
=
your call
 
Back
Top Bottom