Hi I'm Brian, from Pittsburgh. I was hoping you guys would let me tap into the knowledge banks here.

I have been given an assignment for my apprenticeship classes (5th year), where I need to draw a daigram. the diagram must have three momentary pushbutton switches, then operate a lightbulb. the lightbuld will come on only if the switches are pressed in the proper order.

This was simple. three switches in series with holding relays.

To go beyond the basic assignment, for my own enlightenment, I would like to generate a lockout condition if the switches are pressed out of order. I have been trying to pull this off for hours now, I just cant seem to place it, nor can I find any resources online. I'm gettin frusterated!

What I'm asking is that someone direct me somewhere that I can see what this curcuit should look like, or atttach something that would help.

I REALLY appreciate any help you guys give me, thanks!

Sometimes we can make things more complicated than needed.

One possible thought direction. If the correct sequence is A-B-C and R1 is your lock out device.

IF {NOT A AND (B OR C)} OR {IF A AND C} THEN R1

I just drew a ladder with R1 through R3 & a Lockout relay.
1st line: Button A picks R1
2: R1 "a" contact across A seals in R1
3: Button B to node to R1 "a" picks R2
4: R2 "a" contact across B seals in R2
5: Button C to node to R2 "a" to LO "b" contact picks R3
6: R3 "a" contact across C seals in R3, node from line 5 to R2 "b" contact to node.
7: Node from line 3 to R1 "b" contact to node from line 6 to node to pick LO relay.
8: LO "a" contact to line 7 node seals in LO
9: R3 "a" contact lights indicator.
Looks like all relays can be DPDT, with an aux contact available for R3. It could actually be a useful ladder circuit. I can send a jpg or paste it into a Word Doc if you have problems drawing out the ladder from what I posted.
Joe


[This message has been edited by JoeTestingEngr (edited 03-01-2006).]

Joe I'm real close but I just cant get it. I hate to ask it but I would love to see the curcuit you did.

Thanks!

OK, I have sent you and Trumpy a jpg of the ladder. You will either get your bulb or a lockout condition as requested. You didn't ask for key resets or anything like that but interrupting control power will obviously work. You would have to use 3PDT relays for R3 or LO to actually control anything or give remote LO status. You could also use a "Lockout" indicator across the LO coil and a "Standby", "ready", or other appropriate indicator driven off the b contact(NC) from the sme pole that seals in your LO. That way, you always have at least one indicator on. Lastly, don't forget the Terrible Towel
Joe (formerly of the Pittsburgh area)

[This message has been edited by JoeTestingEngr (edited 03-02-2006).]

Here's the diagram Joe,

Thanks Mike!
Of course, looking at it now, I realize that you could just put your indicator in parallel with R3's coil and drive a load on the last line. You could also skip line 9 and show form "c" contacts to the right of line 5 to drive an isolated load. All with 4,DPDT relays.

Here's something else to try.. Put a 1-30 minute Time Delay Operate coil in parallel with your LO coil. Use the NC contact at the top left of your ladder to reset everything > 15 minutes after a failed attempt. Use the isolated contact for access control of this forum's liquor cabinet. Seems to me that the folks around here tend to imbibe heavily while discussing particle physics. It has been common practice to shutdown bars for elections. You can be the first to do it for electrons.
Joe

Brian,
Welcome to the group mate!.
Like yourself, I did a 5 year apprenticeship as an Electrician.
What I will say is thanks for actually asking questions.
A lot of people go through thier "time" never questioning what they are taught.
Those that ask learn more.
Take care,
Mike.

Bump (just for the ladder diagram)