HOA multiple contacts diagram comprehension

[TexasMaster]

From my following example (couldn’t upload a picture) there are several things I have “assumed” to be correct, but in the function of the particular machine I’m working on, I feel I’m misunderstanding something. Assumptions (as I could be wrong in more places than I think)... if an hoa is drawn in its off state, & asterisk are placed on the respective sides of the hand or auto side at each contact, I believe they would oppose the position they’re shown in only when the selection of that position is made.... ex. below, contact 1 n/o, closed in hand only, contact 2 n/o, closed in auto only, & (my most confused) contact 3 n/c, opened only in auto....???

Ps. In previewing the post it looks like my n/o contacts lines get shifted, but I think all would get the idea

(Hand/Off/Auto)
____
1. (X00) 0 0
____
2. (00X) 0 0

3. (00X) 0___0

 

[ptonsparky]

?? What's your question?

 

[gar]

190817-2253 EDT

ptonsparky:

I believe his question is about his interpretation of the symbolism of the Xs and 0s.

He has three contact blocks on the selector switch. Both switches 1 and 2 are mounted as normally open, and number 3 as normally closed.

The X implies the asserted condition. When asserted a NO switch is closed, and when a NC switch is asserted it is opened.

In his diagram:
In HAND switch 1 is closed, 2 is open, and 3 is closed.
In OFF switch 1 is open, 2 is open, and 3 is closed.
In RUN switch 1 is open, 2 is closed, and 3 is open.

This could be done with all NO switches, and different cams.

I believe my comment is a correct description, but those that work with these circuits every day are the ones to answer.

However, TexasMaster could analysis the circuit operation and determine how the selector switch works.

Things could be more complicated when a PLC with transition contacts is used.

.

 

[gar]

190817-2363 EDT

It should be noted that based on my description that switch 3 is really the NOT of switch 2, and this is easily created in a PLC.

.

 

[gar]

190817-2412 EDT

One more small detail.

This could be done with a NO switch 3 and a cam that was XX0. But now if there was a break before make between the 2 Xs, then this could be a problem. Using NOT S2 solves that problem.

.

 

[TexasMaster]

Ptonsparky, I’m mostly checking if I have this concept right... it seems simple, but I have reason to believe I don’t understand it, or I’m looking at a misprint on contact 3.
Thank you Gar. You are correct, in that in person to pull this off, the way the selector switch is cammed, all of the contacts are actually the opposite of what is shown.
Nothing fancy here either, like plc, etc... this is an early ‘80s cotton press. The circuit that breaks though on 3 opens any possibility I see of a “full bale audible” going off... which I’d think is a function of “auto”
I’ll work some more on trying to upload the schematic soon

 

[RumRunner]

Ptonsparky, I’m mostly checking if I have this concept right... it seems simple, but I have reason to believe I don’t understand it, or I’m looking at a misprint on contact 3.
Thank you Gar. You are correct, in that in person to pull this off, the way the selector switch is cammed, all of the contacts are actually the opposite of what is shown.
Nothing fancy here either, like plc, etc... this is an early ‘80s cotton press. The circuit that breaks though on 3 opens any possibility I see of a “full bale audible” going off... which I’d think is a function of “auto”
I’ll work some more on trying to upload the schematic soon

Hi Tex,

Your concept of auto is exactly how auto should work

The perceived N/C contact 3 that should only open in auto-- seem implausible since you have to go through the OFF position when making the transition from HAND to AUTO.

From a safety perspective, anytime you turn a switch off, it means you disable a system. No unintentional act should cause the machine to start.

Control power circuit is still enabled but contacts should be open when in OFF position.

Since you mentioned a “full bale audible” going off (activated) . . .it indicates you have an alarm buzzer, red flashing light or whistle to notify the operator that a bale is done. This is common for those 80s vintage machines.

Along with this alarm system that is incorporated in the circuit, it also receives a feedback signal from the baling machine that a bale is in fact done.

This could be any form of a pressure switch, proximity switch, a photo switch or simply a limit switch activated by the height or size of the bale.

When this switch is activated, it will send a signal to stop the compression.

This is what the AUTO function on your H-O-A selector switch.

Since you did not ask what switch would be suitable for this application and how it is connected. . . I would not cover it.

And please do send an schematic if you can.

 

[TexasMaster]

Anyone else having this problem...

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Image resize failed due to your image library not having support for this image type.”

from my iPhone or desktop

 

[kwired]

I think everyone is having troubles posting images. I just tried to post one to test it out and got similar image library message.

 

[TexasMaster]

1

 

[TexasMaster]

There’s a few more contacts made than I was mentioning, just to get the basic concept out there, but look at the bottom contact. It seems impossible that I would break contact to the pressure switch and buzzer in auto....

 

[Jraef]

There’s a few more contacts made than I was mentioning, just to get the basic concept out there, but look at the bottom contact. It seems impossible that I would break contact to the pressure switch and buzzer in auto....

No, that's not what that means. In this diagram, all of the contacts are shown with the switch in the OFF (center) position. That last rung means that in AUTO, that contact will be REMAINING closed (as it is now in OFF). The only time it will be open then is in the HAND position. I can imagine that it's probably because in HAND, you are immediately energizing the motor, and the Ram FWD, unless someone hits the Ram REV jog button, probably just for setup and testing maybe, therefore no pressure switch and no buzzer.

 

[TexasMaster]

Thanks Jraef, I completely agree, but only from an understanding of the operation necessary to function. However, there’s things I question here:

1) why not draw the asterisk on the hand side? ...as myself, and I see from the replies that others interpret this as -“make” the marked open contacts and “break” the closed contact.

or

2) why not a n/o contact drawn that closes in auto? I cannot see why closed is needed if the machine is off in the first place

3) Last, from your reply, what am I missing that makes this -“REMAINING” logic that doesn’t match the action/logic of any other -so easy for you to recognize? Is this all better stated that they close or remain closed when (*) rather than thinking makes and breaks. Is this diagram different in some way...?

 

[drktmplr12]

Thanks Jraef, I completely agree, but only from an understanding of the operation necessary to function. However, there’s things I question here:

1) why not draw the asterisk on the hand side? ...as myself, and I see from the replies that others interpret this as -“make” the marked open contacts and “break” the closed contact.

or

2) why not a n/o contact drawn that closes in auto? I cannot see why closed is needed if the machine is off in the first place

3) Last, from your reply, what am I missing that makes this -“REMAINING” logic that doesn’t match the action/logic of any other -so easy for you to recognize? Is this all better stated that they close or remain closed when (*) rather than thinking makes and breaks. Is this diagram different in some way...?

1) because the switch is closed in both the OFF and AUTO position. OXX is what a modern schematic would show.

2) my best guess is the designer decided that the alarm should only be disabled when in HAND. this arrangement accomplishes that.

3) i don't think of it as makes and breaks, although that is what the cam is physically doing. it's drawn assuming the machine is off, the asterisks indicate the position where the switch is closed.

from top to bottom:

XOO
OOX
OOX
XOO
OOX
OXX

that's how I see it at least.

 

[kwired]

1) because the switch is closed in both the OFF and AUTO position. OXX is what a modern schematic would show.

2) my best guess is the designer decided that the alarm should only be disabled when in HAND. this arrangement accomplishes that.

3) i don't think of it as makes and breaks, although that is what the cam is physically doing. it's drawn assuming the machine is off, the asterisks indicate the position where the switch is closed.

from top to bottom:

XOO
OOX
OOX
XOO
OOX
OXX

that's how I see it at least.

Probably so, but I think the moving contact bar for the switch in question should be on the top side instead of the bottom side, still in a closed postion to represent state in the "off" position.

And the other two contacts that close when in HAND should have had the moving contact bar on the bottom side as well.

This for a simple cam that would operate a a standard NO contact on each side of switch in an ON/OFF/ON manner, which seems to be the most common application. If a different or more complex cam is used then more details are necessary to tell which state the contact is in in each switch position.

 

[Jraef]

With selector switches, there are two independent aspects of the contact sets used on them; the “Normal” condition of the contacts, ie NO or NC, and the “cam” inside of the mechanism that changes their state. The relationship between the two can be complex and confusing. But as a general rule, contacts in an HOA switch arrangement are shown like they are here, with the switch in the center OFF position, and whether the contact blocks themselves are NO or NC is depicted by their placement in the diagram as above the line for NC contacts, below the line for NO contacts. So that drawing tells me that it is a NC contact block and the cam on the switch will not change its state in the OFF or AUTO position, leaving it to change state only in the HAND position.