Physical relays required from SOP with 2 outputs

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littlej040
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Hi all,

I'm looking to control two outputs using (3) 12 V coil relays, with the SOP of the truth table listed as below:

A' B C' + A' B C
simplified to:
= A' B ( C + C')
= A' B ----> Y0

A B C' + A' B C'
simplified to:
= B C' (A + A')
=B C' ------> Y1

The problem I am having is to spec out the required relays to make this work. As you can see input B is common to both outputs, so I am expecting to use a DPDT for Relay B, but am not completely certain.

Any help provided with specing the required relays and the wiring is greatly appreciated.
 

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I made a mistake, I would be using a SPDT relay for "input B", in this case an indication of when a blower is turning on. I am getting a bit befuddled on my wiring from the relay contacts from input A -> input B however.
 
Anyone have any input?
 
littlej040 said:
Hi all,

I'm looking to control two outputs using (3) 12 V coil relays, with the SOP of the truth table listed as below:

A' B C' + A' B C
simplified to:
= A' B ( C + C')
= A' B ----> Y0

A B C' + A' B C'
simplified to:
= B C' (A + A')
=B C' ------> Y1

The problem I am having is to spec out the required relays to make this work. As you can see input B is common to both outputs, so I am expecting to use a DPDT for Relay B, but am not completely certain.

Any help provided with specing the required relays and the wiring is greatly appreciated.

littlej040 said:
I made a mistake, I would be using a SPDT relay for "input B", in this case an indication of when a blower is turning on. I am getting a bit befuddled on my wiring from the relay contacts from input A -> input B however.

What is the context of the question? What is the application?

Are you saying that you have to use the inputs straight to the relays, instead of using logic gates to give you a single signal to drive each relay? Why?
 
The application is for a biological safety cabinet in which I am trying to control power to an external airflow monitor and blower enabling switch. I am limited to using strictly relay logic vs. other methods due to the fact that I will have to be doing this as an "in field" replacement kit for some of our older products.

I would have much preferred to do this with a simple PLC program, but am limited by what the customers have. I keep running down the same road where I am trying to switch outputs simply using dry relay contacts, but realize I need to daisy chain contacts to the conditional relays coils.
 
littlej040 said:
The application is for a biological safety cabinet in which I am trying to control power to an external airflow monitor and blower enabling switch. I am limited to using strictly relay logic vs. other methods due to the fact that I will have to be doing this as an "in field" replacement kit for some of our older products.

I would have much preferred to do this with a simple PLC program, but am limited by what the customers have. I keep running down the same road where I am trying to switch outputs simply using dry relay contacts, but realize I need to daisy chain contacts to the conditional relays coils.

So it looks like for each of the relays, you need one input low and the other input high. Can you use this low/high combination to drive the ends of the coil for each relay? You can put a diode in series to select which low/high combination will drive current through the coil.