Ladder Diagram for DG Type 4-way valve(spring centered) 1

[robel82]

First off, Im not sure if im in the right forum or not, if so for the inconvience.

I need to design an electrical ladder diagram, given three limit switches(LS), which will move a hydraulic cylinder in the following sequence:

-cylinder extends when LS1 is activated
-cylinder retracts when it activates LS3
-cylinder stops on its retraction cycle when it activates LS2
-after 10 seconds the cylinder continues to LS1

Switches are as:

[cylinder]------> o o o
| | |
LS1 LS2 LS3

If anyone can provide any helpful insight it would be very much appreciated.

 

[lighterup]

I don't know anything about the valve of which you speak, but I have a working ladder diagram which performs the operations you describe. If you can post your email I can send a jpg of it. I could not figure a way to post it directly to the thread.

 

[itsmoked]

lighterup; Emails in posts are a big no-no. Attracts pests.

Post your jpg!! I'd like to see it as others might too.
Check my FAQ:
faq238-1161

Keep in mind it is even easier to do then explain. Takes me about 45 seconds to post a picture, to give you the idea.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[lighterup]

OK, not sure I got all that, but we'll see.

This is hard to read, the upper contacts of LS3 and LS2 are NC, and the bottom are NO. TMR is a simple delay timer which after activated delays 10 seconds and makes the contacts. When energy is removed from TMR, (LS2 breaks), the TMR contacts immediately go to "normal" positions. The mechanical adjustment of LS2 must be such that it breaks the path to RET before the NO TMR contact breaks.
Thanks, smoked

 

[lighterup]

Forgot to mention, the ladder shown will just sit and cycle the cylinder continuously. If you want to manually initiate the cycle, put a manual switch in the top line in series with the LS1/Extend latching circuit.

 

[itsmoked]

Nope you bollixed it up! But we can still see it by clicking the visible link on your post. So tiz not a problem.

For your info you almost had it you just needed to put the

http://i2.tinypic.com/rbig7c.jpg

inside square brackets and add "img" like this:

[ignore]

[/ignore]

I'll do it here:

Now if someone who does a lot of ladder logic comes along...

 

[robel82]

that is good ligherup. thank you

are the 'Extend' and 'Return' outputs relays? im not familiar with this terminology. also i dont see the selonoids in the diagram, shouldnt they be included?

 

[Skogsgurra]

Extend and Return ARE the solenoids. Or, if the outputs can't handle them, the relays that control the solenoids.

Comment to the diagram: It works OK until starting from LS2 on its way home. TMR then loses its input and drops so that the movement is stopped "half an inch" from LS2. Needs a holding circuit (that is opened by LS1) for the home travel.

Gunnar Englund

http://www.gke.org

 

[lighterup]

It has been 20 years since I did this stuff, but as I recall, some limit switches have a mechanical hysteresis adjustment to cause the break of the NO contact to occur slightly after the closure of the NC contact. This would cause the paths (NOT(LS2) AND Return) and TMR to both be closed for a few milliseconds until the NO contact of LS2 de-energizes TMR, which would hold the Return relay on long enough to latch Return through (NOT(LS2) AND Return) for the trip home. That is why I included the comment about the mechanical adjustment of LS2 in my original post.
Larry Richardson

 

[waross]

Hello robel82 and others.
Thanks for the posting tip, itsmoked.
To put skogsgurra's post in other words; You have a circuit race with LS2. There is a short interval between the opening of one set of contacts and the closing of the other set of contacts.
This is bad design practice.
It will probably work with relays, BUT;
If timer opening time is less than LS2 transfer time, the circuit will fail.
The circuit may have problems if applied to a PLC, the effect of circuit race in a PLC depends on the internal scanning protocol of the individual PLC. I once developed a "Circuit Race" demonstration circuit that behaved differently on three different PLCs with different scanning protocols.
skog, the diagram is calling up auxilliary contacts on "extend" and "return" so they must be relays.
robel82 The extend and return solenoid will be in parallel with the extend and return relays, or better controlled by contacts on the extend and return relays.
respectfully

 

[Skogsgurra]

Yes, some kind of overlapping would probably do it.

Gunnar Englund

http://www.gke.org

 

[lighterup]

OK,
Guess it has been awhile. Since timers and such are cheap in PLC-land, here is a version with a delay-off timer which can be adjusted to insure that LS2 does not stop the homeward journey. Help me out here, you PLC jocks.