relay

[mikeames]

I fully agree with weressl. I woudl have written it my self if he didnt. I dont feel the NC / NO termonology is confusing at all. I feel its a standard that all in our feild should know and understand.... "Ladder logic 101" if that confuses people then they need to study up. I also agree that dynamic devices such as Pressure and temp sensors add complexity to logic diagrams but if you follw the "default" states its not so bad.

 

[charlie b]

That is why it important to define that the NO and NC states mean off-the-shelf condition. Ladder 101.

I would prefer to continue my campaign to forever eliminate the "n-word" ("normally") from our vocabulary. Just one of many campaigns that I am destined to lose, alas. :wink:

 

[weressl]

I would prefer to continue my campaign to forever eliminate the "n-word" ("normally") from our vocabulary. Just one of many campaigns that I am destined to lose, alas. :wink:

yep, that's why I have callus on my forehead

 

[jim dungar]

3 position switches should indicate the status of the contacts in each position.

You have your way and I have mine. I use a small truth table next to each contact, the middle position of an Off-Stop-Start switch would look something like oxx.

Simple phrases like 'normally open' and 'normally closed' can only describe two states.

 

[pbeasley]

How about a book?

How about a book?

All of my ladder skills I have learned the hard way. Can anyone recommend a decent mid-level book on the subject? In this case sticking with non-PLC applications...

 

[weressl]

You have your way and I have mine. I use a small truth table next to each contact, the middle position of an Off-Stop-Start switch would look something like oxx.

Simple phrases like 'normally open' and 'normally closed' can only describe two states.

If you read my posting carefuly that IS an emebedded truth taple in the graphic, not separate from it.

I am unaware of other than two position of a binary device.:smile:

 

[jim dungar]

Laszlo,

The primary difference between your method and mine, is the lack of the vertical line connecting the state of the contacts. I feel that this extra line serves little purpose and can easily clutter up a drawing, especially where the contacts of the switch/device may be separated by several lines of logic.

 

[weressl]

Laszlo,

The primary difference between your method and mine, is the lack of the vertical line connecting the state of the contacts. I feel that this extra line serves little purpose and can easily clutter up a drawing, especially where the contacts of the switch/device may be separated by several lines of logic.

Yes and no. It is a question of representation. You already WOULD have the vertical line for the operator itself, so even if there are several lines of logic between the contacts, the operator control line would need to be connected between the contacts, indicating that they are controlled by a common mechanical link. The adjacent vertical lines - indicating the alternate positions - would be just additions to the existing one and since they are dashed lightweight lines, they represent less 'clutter' than the man heavy line itself.

It is a choice. The smart choice - IMHO - is either of the following:

1. Do not interject any logic lines within a single device.
2. If individual contacts are separated by logic lines, do not connect the operator, but redraw the operator at each separated contact(or group of contacts).

When the swicth is more than just a HOA or Stop-Run-Start, like a drumswitch on crane or other multiposition witch the logic truth table is the way to go. But then one uses relay type contacts, as opposed to push operated type, and all contacts ar shown in the open position. Each contact has a sub-number and in the position matrix and X would indicate which contact is closed in what position. Dash between adjacent X positions indicate that the contact does not open during transition from one position to the other.