Which one is it?

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Which is it? Post #22

Q: Assume that a program rung consist of an OTE instuction only. The output would then be?
A: I say continuously on, my lab partner says shorted.
Thanks!
 
Maybe your and/or your partner arent absorbing the concept behind ladder logic. It originated from Relay Ladder Logic, which used relays to perform all the functions the plc can now do.

How did they come up with the ladder, well lets start with a control voltage say 120 volt. Now we represent this voltage on paper


120v                                             Neutral

 |                                                  |

 |                                                  |

.
I assume you learned that a relay is a device that can be actuated via electricity and has contacts that can be either Normally open or normally closed or a combo of both. Now think what happens when a relay is connected to the 120v control ckt.


|-------------------------------------------(relay)-|

.
Since there are no switches etc in front of the relay's actuating coil then it will turn ON and stay ON as long as power is ON

This is hardware implementation, with plc's what you are doing is software representation of the equivalent....therefore


|-------------------------------------------(OTE)---|

.
will be the equivalent of the ckt above with the relay.
It will always be ON
 
Some PLCs are sensitive about no conditions on a rung before the output. You may check your specific PLC documentation. AutomationDirect (if not on the first rung of the program or a section) will merge the output with the previous rung.
 
Bernie

AutomationDirect (if not on the first rung of the program or a section) will merge the output with the previous rung.
Click to expand...

As far as I know, the situation is the same with Simatic S5, Simatic S7 (both 200 and 300/400), Omron CQM1, Philips PC20/MC30, Allen-Bradley CompactLogix. And I think for a lot of athers.

Kind regards,

Jean Pierre Vandecandelaere
Instructor PLC - SCADA
 
ote always on

Every ote between the Line (volt) and the neutral in a electric plan stay on.

It's the same thing in plc ladder, but the ladder number where the OTE is, must be scan

Line neutral
-----------------(ote)-----|
 
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