Shared 'dry contacts'

[hbiss]

200409-

hbiss:

See post Tuesday 2:06 PM. A logical AND.

..

I was making it too hard. Typical. Point A will supply us 24VDC, run it out 2000' through a set of NO contacts controlled at Point B, then back through another NO set of contacts controlled at point A. If both closed we get a run command. Either drops or fails to close we get a stop command.

Ahh, OK. Logical "AND" it is now.

-Hal

 

[ptonsparky]

To make it simpler, can I use two identical timers that use terminals 5 & 6 as an initiation input connected to the same set of NO contacts? Ignore any distance at the moment. Not something I would do normally but that was essentially my original question.

 

[__dan]

It's still not clear what you want to do. I've never seen a center pivot irrigation system and cannot guess at the detailed requirements.

From what I've gathered so far, two equipment locations, A and B. Independent starting at A or B (starting one well pump?). And independent fault safety trip at either A or B (A and B both must be OK to run). A or B call for water, A and B both must be not tripped to run.

If so, I can try to modify the earlier drawing along the same earlier premise. Is that what you want?

 

[gar]

200409-1810 EDT

ptonsparky:

If you have a time delay relay that requires an isolated contact closure between terminals 5 and 6 and that must remain closed tp function and that has a delay to closure of an isolated contact, then that relay can to be used to modify the the function of your present contact. In other words produce a delayed output. Usually such a delay relay will open the output contact on loss of the input closure.

Because the outputs are ANDed together there is no need for precisely identical time delays.

.

 

[ptonsparky]

View attachment dry.JPG

 

[gar]

200409-2330 EDT

ptonsparky:

Sorry but I do not understand what your .pdf is telling me.

.

 

[Open Neutral]

You actually have 3 conductors: one is ground.
(No one said it had to be line voltage control....)

 

[ptonsparky]

It's still not clear what you want to do. I've never seen a center pivot irrigation system and cannot guess at the detailed requirements. Think a single motor running a hydraulic pump with high and low pressure limits. Simple as that at A&B locations.

From what I've gathered so far, two equipment locations, A and B. Independent starting at A or B (starting one well pump?). The well, controlled by POCO, starts A&B as water pressure comes up. And independent fault safety trip at either A or B (A and B both must be OK to run). A or B call for water, A and B both must be not tripped to run. A&B do not call for water but once they have pressure it must be maintained to keep the Well running. Radio communications allow for a 15 minute delay after start of the well and pressure acknowledgment at A&B. No confirmation or loss of pressure, stops well until POCO recycles power again.

If so, I can try to modify the earlier drawing along the same earlier premise. Is that what you want?

Not neccessary to modify your drawings. Up to you, but I think we have it figured out without having to build it from scratch. No local Radio Shack means no experimentation for me anymore.

Thank you.

I do appreciate the help all of you take the time to give.

 

[ptonsparky]

You actually have 3 conductors: one is ground.
(No one said it had to be line voltage control....)

I thought of it.

 

[ptonsparky]

200409-2330 EDT

ptonsparky:

Sorry but I do not understand what your .pdf is telling me.

.

That diagram comes from software I use to simulate the solutions before build. I should have indicated the two NO contacts go to terminals 5&6 of each timer with a space of 2000' between them. There are two different power sources for the timers. It was late. The software indicates my solution was viable. I wouldn't bet on it at 2000' even without sharing inputs. Next time I have a spare $150 to play with I'll buy a couple timers and try it.

 

[kwired]

I was making it too hard. Typical. Point A will supply us 24VDC, run it out 2000' through a set of NO contacts controlled at Point B, then back through another NO set of contacts controlled at point A. If both closed we get a run command. Either drops or fails to close we get a stop command.

This explanation makes sense, but your contacts are in series giving you an "and" function to the logic of this segment of the controls but you first said they would be parallel and was describing more of an "or" function.

You later described your application a little better - I think the "and" function is what you are needing, both pivots must be running to close the two contacts that are in series with whatever circuit is controlling the well.

 

[ptonsparky]

This explanation makes sense, but your contacts are in series giving you an "and" function to the logic of this segment of the controls but you first said they would be parallel and was describing more of an "or" function.

You later described your application a little better - I think the "and" function is what you are needing, both pivots must be running to close the two contacts that are in series with whatever circuit is controlling the well.

My original question was with the dry contacts in parallel to two timers.

My solution is series with no timers.

 

[kwired]

Pretty much.

We had a full pivot and two pivot corners that were going to run separately from one well. None at the same time. Turns out well pumps way too much water and unless we added $xx,xxx VFD we were going to exceed psi rating of 30 year old buried pipe. We were set up as requested originally to run one corner or the other with radio controls. Two transmitters with one receiver at the well. We should be able to return one transmitter now.

Sounds like simple solution might be a pressure switch used as a high limit switch. If correct use of water is not enabled (guessing manually actuated control valves is used for this) then well shuts down because pressure is too high, need to set up as a lockout scheme, it may "recycle" if power is lost
and then lock out again.

 

[gar]

299410-2119 EDT

ptonsparky:

I still have no idea what your drawing means. I see no inputs, and what do the outputs do? i have no way to logically understand the drawing. It is just plain Greek.

Like what is a one-shot. How does the one-shot work? How many inputs? Are these referenced to a common? is it edge triggered, or do I need to differential an input signal? Or maintain a trigger for at least the full duration? What is the reset input and why is it needed? What happens if the input trigger lasts longer than the output pulse duration? And many other questions.

What do the one-shot outputs do, and why the need for one-shots?

.

 

[ptonsparky]

299410-2119 EDT

ptonsparky:

I still have no idea what your drawing means. I see no inputs, and what do the outputs do? i have no way to logically understand the drawing. It is just plain Greek.

Like what is a one-shot. How does the one-shot work? How many inputs? Are these referenced to a common? is it edge triggered, or do I need to differential an input signal? Or maintain a trigger for at least the full duration? What is the reset input and why is it needed? What happens if the input trigger lasts longer than the output pulse duration? And many other questions.

What do the one-shot outputs do, and why the need for one-shots?

.

I feel so much better now. i would feel better if I was fluent enough to explain it all in 100 words or less. I’ll give it a shot later.

Grass to mow in the morning then I need to make sure the snow blower is tuned up for Easter.

 

[gar]

200410-2344 EDT

ptonsparky:

If the asserted condition to initiate your single-shot device is a logic 0, then a pair of parallel contacts form a logic 1 source will perform the logical "AND" function when both contacts are open and the output falls to logic 0.

For example: if you take the output of a NAND gate that is performing an "AND" function feeding the input to another NAND, then the second NAND gate is performing an "OR" function. You would need the output of the first NAND to be NOTed before going to the second NAND for the second NAND to be an "AND" function.

If in the above the second NAND was a NOR and fed from the first NAND output, then the NOR would perform the "AND" function.

,

 

[__dan]

Normally I would be looking for a sequence of operation or a reference design, the way everyone else does it. That's the place to start.

Sequence of Operation (guessing):
Call for water
Trial run of the pump on a timer to allow pressure to build.
After trial timer run, monitor pressure (analog or setpoint pressure switches)
Disable pump for low pressure (suspect broken pipe or pump fail to run)
Disable pump for high pressure (suspect blocked pipe or load side equipment failure)
Disable pump for fault and safety trips
End call for water

 

[ptonsparky]

The control sequence of the whole project after the relay is not relevant to the OP. One shot, repeatability, Delay on Make, Delay on Break, Pulse or the time set points is of no consequence.

I know Gar does not like the term Dry contacts. I did not coin it. They require no outside source of power other than what comes from the relay itself. I do not know the open voltage of this supply, if it is AC or DC or the current that must flow when the circuit is complete. Each relay is feed from a different control transformer.

The question was: Can two identical relays share the same contact or pair of contacts to initiate the timer sequence? Whatever they may be.

I suspect it may work at close distances but not @ 2k feet. IDK. We are using a different method for this project so the question is moot, for now.

 

[hillbilly1]

Dry contacts are no longer dry (absence of voltage) once used in a circuit. Voltage is applied to provide a function, whether to power a coil, start a timer, etc. If the control power at both ends is the same circuit or output, then no problem, but if they are different circuits, then they would be paralleled.

 

[gar]

200410-1633 EDT

ptonsparly:

My answer to your question
"The question was: Can two identical relays share the same contact or pair of contacts to initiate the timer sequence? Whatever they may be."
is ---

If timer means one timer with one input to initiate the timer, and a contact closure to that timer initiates the timer, then any combination of isolated contacts connected together in any combinatorial fashion to form the equivalent of one contact can initiate the timer. When that combination of contacts makes closure of the combination's output is determined by the logic of that combination. Those contacts can come from different sources, relays, switches, or other things.

When speaking of ordinary electromechanical relays it is usually assumed that each output contact pair is isolated from anything else until connected to something else. A contact pair is one switch. It takes two contacts to make one switch.

A slight disparity is that there are many relays with a SPDT type of contact structure where there are really three contacts which is really two contact pairs, one NO and the other NC sharing a common relay terminal.

I believe this answer is not correct for your question, and therefore I need a more precise description of the question.

.

. .