Shared 'dry contacts'

[kwired]

My understanding is that "dry contact" refers to any relay, switch, whatever which is not a SOURCE of power under normal conditions. A controller might output 12VDC when some function is performed on whatever controls that. If an application required "dry contacts", that 12VDC could then be used to control the coil on a relay having the appropriate ratings. If the controller only provided "dry contacts", a source of power to control a relay, and another to provide the power, would be required.

Do I have that wrong?

IDK but I think many would consider solid state control device to not be a dry contact even if it is performing a similar function as a mechanical contact.

 

[hbiss]

IDK but I think many would consider solid state control device to not be a dry contact even if it is performing a similar function as a mechanical contact.

That would be correct.

-Hal

 

[gar]

200413-1303 EDT

First, we need to get rid of this "dry contact" stuff. An ordinary toggle switch unconnected to anything sitting in your hand is just a contact plain and simple. The singular use of the word "contact" in switching or logic theory is simply a device that has two states. Ideally completely open or closed.

Until a contact is wired into a circuit it is floating, connected to nothing. A real world electromechanical contact (switch) is really made up of two separate conductive contacts that can be made to touch or not When the word "contact" (singular form) is used in describing a circuit component it is really synonymous with "switch".

kwired:

My previous discussion on the possible operation of the pivot system is nonsense. Your description provides a much better basis to start from.

But first ptonsparkly's posts were:

"Tuesday 10 AM

Change of plans now that 2000' of wire is buried. nice We have a pair of #12 control wires in the raceway that were not needed originally.

Point A has control and dry contacts. Point B has a control and dry contacts. I would like to parallel the two contacts so that if either closes, it cycles both controls.
Workable or will one interfer with the other? That and distance laying directly next to 480. "

And

"Tuesday 2 PM

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."

And

'Tuesday 2:14 PM

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."

And

"Tuesday 2:22 PM

Yes, each pivot motor will start on pressure from the remote well, closing a well relay. Each pivot has a safety circuit that will trip open the well relay circuit should something go wrong. The radio transmitter and receiver talk so it knows when the well has started and allows for time to elapse before sending a Stop. System will attempt restart at each POCO cycle of power."

And

"Thursday 5:42 PM

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."

And

"Friday 9:13 AN

__dan said:
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. "

And

"Friday 9:30 AM

Skipping it"

And

"Friday 9:41 AM

kwired said:
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. "

And

I will continue later working from kwired description of how the system may work.

..







cpmyact

 

[kwired]

200413-1303 EDT

First, we need to get rid of this "dry contact" stuff. An ordinary toggle switch unconnected to anything sitting in your hand is just a contact plain and simple. The singular use of the word "contact" in switching or logic theory is simply a device that has two states. Ideally completely open or closed.

Until a contact is wired into a circuit it is floating, connected to nothing. A real world electromechanical contact (switch) is really made up of two separate conductive contacts that can be made to touch or not When the word "contact" (singular form) is used in describing a circuit component it is really synonymous with "switch".

kwired:

My previous discussion on the possible operation of the pivot system is nonsense. Your description provides a much better basis to start from.

But first ptonsparkly's posts were:

"Tuesday 10 AM

Change of plans now that 2000' of wire is buried. nice We have a pair of #12 control wires in the raceway that were not needed originally.

Point A has control and dry contacts. Point B has a control and dry contacts. I would like to parallel the two contacts so that if either closes, it cycles both controls.
Workable or will one interfer with the other? That and distance laying directly next to 480. "

And

"Tuesday 2 PM

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."

And

'Tuesday 2:14 PM

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."

And

"Tuesday 2:22 PM

Yes, each pivot motor will start on pressure from the remote well, closing a well relay. Each pivot has a safety circuit that will trip open the well relay circuit should something go wrong. The radio transmitter and receiver talk so it knows when the well has started and allows for time to elapse before sending a Stop. System will attempt restart at each POCO cycle of power."

And

"Thursday 5:42 PM

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."

And

"Friday 9:13 AN

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. "

And

"Friday 9:30 AM

Skipping it"

And

"Friday 9:41 AM

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

My solution is series with no timers. "

And

I will continue later working from kwired description of how the system may work.

..







cpmyact

I have to admit I had difficulty following exactly what he is up to as well, but also will say I likely have more knowledge of these systems than many that use this site have and know what is typical and what user's intended use may be like.

 

[ptonsparky]

I am raising the anchor on the Good Ship Lollypop.

Look at the my post 50. Lower right of that pamphlet shows exactly the timer I was thinking of. Look at terminals 5&6. It has a switch floating out there not too far away. Nothing connected to it. Connect that switch to 5&6. That timer is at Point A. Duplicate the timer set up at Point B.
Now connect a pair of wires to 5 & 6.
Point A 5--------5 Point B
Point A 6--------6 Point B

Will the closure of either switch activate both timer sequences?

Note does say they should be shielded. SOL.

 

[__dan]

When the timer external pushbutton is closed, there will be no problem and each timer will see the low impedance, control current flow activating the timer internal on state, led optoisolated or not.

When the timer external pushbutton is open, each timer's internal power supply will be paralleled with the other. That's a no no, undefined behaviour, or worse, unintended behaviour.

That's when you would want an isolating or interposing relay trigering from the external pushbutton to give you two isolated timer input contacts.

Two different contact blocks on the same pushbutton would also be beautiful for the application, one for each timer. One pole contact for two differently and independently powered control circuits, no. Two pole contacts on the pushbutton or an interposing isolating relay, one pole for each timer, yes.

Excuse me, timer internal power supplies are not paralleled, they are in a big series loop. Two independent different timer internal power supplies AND two different timer internal sense loads (optoisolator type would be the standard) would all be in series at that point. The best that can be said is it would be undefined behaviour, not in the spec or in the manufacturer instructions, nor would it be. It is a no no.

 

[ptonsparky]

When the timer external pushbutton is closed, there will be no problem and each timer will see the low impedance, control current flow activating the timer internal on state, led optoisolated or not.

When the timer external pushbutton is open, each timer's internal power supply will be paralleled with the other. That's a no no, undefined behaviour, or worse, unintended behaviour. My concern not knowing how 5&6 were powered internally.

That's when you would want an isolating or interposing relay trigering from the external pushbutton to give you two isolated timer input contacts.
Essentially what we decided.
Two different contact blocks on the same pushbutton would also be beautiful for the application, one for each timer. One pole contact for two differently and independently powered control circuits, no. Two pole contacts on the pushbutton or an interposing isolating relay, one pole for each timer, yes.

 

[__dan]

How the timer is internally powered, if they spec shielded cable for the input, they are admitting it is not noise immune and probably powers from the same voltage as the rest of the chip, could be 5 V DC and very cheaply built 5 VDC. It's probably optoisolated at the input but they're not going to have a second power supply just for the control input.

So any induced voltage from the adjacent wiring could trigger the on state, because it would not take much to light the led and fire the timer. I would advise putting the interposing relay very close to the timer, in the same cabinet, same for each timer. The interposing relay 2k ft away could / would be trouble.

Then control power for the interposing relay, you would have your choice, but the induced voltage noise would have a much harder time pulling in a mechanical relay coil. If that did happen, you could add the ballasting resistor to the coil in parallel.

 

[gar]

200413-2130 EDT

kwired:

I want to start tom your post of Yesterday 1:14 PM. part of which follows:

" ---- The well is probably sized to supply the full system. Is oversized for the small systems, but using two of those smaller systems at same time gets at least much closer to well design.

Likely there is manually actuated valves or even reconnection of piping sections when running the full system vs the corner pivots.

The corner pivots need interlocked somehow with well so that if one would shut down the well will shut down, otherwise you continue to pump water through a system that is not moving and this will overwater that area of the field, and worse yet if you are injecting fertilizer or pesticides into the system you over apply to a limited area.

The timers I am guessing is maybe a delay to bypass pressure sensing long enough for normal pressure to build during startup or something of that sort of nature."

We need to know what closure of contact A or B means? I will assume it ,means that at least the associated motor that moves the pivot is powered. May also include that water pressure is adequate.

The AND of contacts A and B are really used to shut down the pump, not to start the pump. After some startup procedure, something else gets the pump running, and after some initial time the AND of A and B must be true for the pump to run. Loss of either A or B causes the pump to stop.

ptonsparky has mentioned the power company shutting off power, and then restarting power. How does this fit in?

There is a lot of missing information on the desired logic.

.

.

 

[kwired]

200413-2130 EDT

kwired:

I want to start tom your post of Yesterday 1:14 PM. part of which follows:

" ---- The well is probably sized to supply the full system. Is oversized for the small systems, but using two of those smaller systems at same time gets at least much closer to well design.

Likely there is manually actuated valves or even reconnection of piping sections when running the full system vs the corner pivots.

The corner pivots need interlocked somehow with well so that if one would shut down the well will shut down, otherwise you continue to pump water through a system that is not moving and this will overwater that area of the field, and worse yet if you are injecting fertilizer or pesticides into the system you over apply to a limited area.

The timers I am guessing is maybe a delay to bypass pressure sensing long enough for normal pressure to build during startup or something of that sort of nature."

We need to know what closure of contact A or B means? I will assume it ,means that at least the associated motor that moves the pivot is powered. May also include that water pressure is adequate.

The AND of contacts A and B are really used to shut down the pump, not to start the pump. After some startup procedure, something else gets the pump running, and after some initial time the AND of A and B must be true for the pump to run. Loss of either A or B causes the pump to stop.

ptonsparky has mentioned the power company shutting off power, and then restarting power. How does this fit in?

There is a lot of missing information on the desired logic.

.

.

Something that also is common, to get better rates you agree to let them control your load during peak demand, they do this with a radio controller that typically interrupts the control circuit to the well pump as it is the major load they are wanting to control. Many farmers want to set their systems up so they will automatically restart once power is restored. Some newer systems have factory installed controls that will do this, you still may need additional relays depending on your circumstances to make it work. Older systems we usually need to add our own relays/timers etc to accomplish what is desired. Often a time delay is needed to allow time for system to build water pressure before you let the pressure switch take over which is intended to shut the pivot down if pressure is lost. But at same time you need a signal to tell the well it needs to run when the pivot is running so it isn't pumping water into a pivot that is not going to move. On top of that you usually need some "manual" switch positions for those times when you want to move the pivot without pumping water like moving to plant or harvest - usually simple bypass of the pressure switch.

Seldom would you run the well without running pivot, but pump panel has hand off auto switch factory installed and is already set up to do so. can still be handy when just doing some testing of the well or even occasionally they may divert water from pivot and fill a tank or something like to water cattle during non growing season. Even been cases where there was fire trucks fighting a rural fire and they find a nearby irrigation well and make arrangements with owner to refill their trucks vs having to take them back to town to do so, most farmers are good about helping in any way they can in such incidents.

 

[ptonsparky]

Kwire:

I think this is similar to what will be there. Three of them. Plus the well pump panel done thirty years ago. There may be a diagram in a drawer somewhere.
No two wire interlock to the Full circle that is 1300 feet away. Never was. Add the new transmitter and receiver. Oh, the POCO load control was moved from the original pivot point to just below the transformer bank as is normal now. There will be no additional timers.

 

[ptonsparky]

The corners used to be pipe irrigation.

 

[kwired]

So the pivots are actuated by water pressure if you have everything set right.

This is easy to do with T-L systems, even if not originally set up to be actuated by pressure.

Gets more complex if you want to shut down the well if the pivot is shut down because of a safety feature shutting it down though motor overload and hydraulic pressure monitors are the easier things to interlock with the well.

If you would have your water supply line break or something of that nature the well will continue to run but the pivot never starts because it is waiting for water pressure before it will start and you need to get more creative to determine how to detect such things if that is desired. Still have to keep it simple enough for operator or they will bypass all your monitoring whenever they think it isn't doing what they think it should do. An owner likely calls you out to make it right, if an employee is the one operating these systems they might not tell anyone and just run things in hand/manual modes. Then you won't get called out until something more catastrophic happens, like the well pumped water for three hours out of a broken/disconnected pipe or into a pivot that was not moving.

 

[gar]

200414-1632 EDT

Apparently at each pivot we have a contact that can tell us something.

1. What does closure of this contact tell us?
2. Does this one bit of information tell us all we need to know about this one pivot?

3. When we have two pivots, and connect their individual contacts in series does the resulting one bit of information tell us all that we need to know? Or do we also need to know which pivot or pivots are the origin of the problem?

.

 

[kwired]

200414-1632 EDT

Apparently at each pivot we have a contact that can tell us something.

1. What does closure of this contact tell us?
2. Does this one bit of information tell us all we need to know about this one pivot?

3. When we have two pivots, and connect their individual contacts in series does the resulting one bit of information tell us all that we need to know? Or do we also need to know which pivot or pivots are the origin of the problem?

.

Can be either way depending on situation. And often times instead of a contact at the pivot we have an output signal that originates from pivot and a relay at the well controller to tell us the pivot is "running" which pulls in a control relay at the well. That is pretty typical with electric motor driven pivots, the ones in OP are a little different breed of machine and the main power for pivot is a hydraulic pump motor and the pivot is hydraulically driven. The way their control panels are made up it is pretty easy to make them automatically start on water pressure and is sort of opposite from electric driven pivots, which is generally easier to start the pivot and it tells the well to run. Either way is simple with one well and one pivot, but can get complex with one well and multiple pivots. Even had some occasions where there was one pivot and two wells, there you need to monitor that both wells are running somehow or else you don't get the amount of water you were expecting applied to the crop.

Then throw in the fact that the well isn't always electric, can be a diesel engine driving the well, and often a generator to run the pivot in that situation. There if the engine quits the pivot also quits because it has no power, but you still need a signal to shut the well down if the pivot stops for some reason or you will overwater the spot where it stopped.

 

[gar]

200415-1450 EDT

kwired:

My first question of my yesterday's post was:

"1. What does closure of this contact tell us?"

Contact means a one bit binary signal. That could be a smoke signal, a two position flag, a light signal, a radio signal, a mechanical switch, or anything else that can have two different states.

In other words is there any more information needed from the pivot than can be provided from a one bit signal?

.

 

[kwired]

200415-1450 EDT

kwired:

My first question of my yesterday's post was:

"1. What does closure of this contact tell us?"

Contact means a one bit binary signal. That could be a smoke signal, a two position flag, a light signal, a radio signal, a mechanical switch, or anything else that can have two different states.

In other words is there any more information needed from the pivot than can be provided from a one bit signal?

.

I understand. When well and pivot are in close proximity to one another it is less costly to do certain things than if they are long distance apart. Pretty common to bury power conductors and two control conductors between pivot and well, then find out later it would be nice to get functions that require either additional control conductors or creative thinking of how to make it work (possibly not quite the way you wanted) with more complex control scheme.

 

[gar]

200422-0846 EDT

I am going to somewhat start over.

Two contacts in series or parallel can perform either the "AND" ot "OR" function. It is simply a function of definitions.

When a closed contact means "TRUE", then two in series form an "AND" circuit,

When an open contact means "TRUE", then two in parallel form an "AND" circuit. I call this negative logic.

If I take any combination of switches (contacts) and form a network that ends up as just two terminals, then I get only one bit of output information, "TRUE" or "FALSE". There may be many different switch combinations that produce a "TRUE" or "FALSE" output, but there are only two output states.

In ptonsparky's case there is only one bit of useful information. This bit is OK to keep pump running, or stop pump. Can not be used to start or restart pump.

.

 

[kwired]

200422-0846 EDT

I am going to somewhat start over.

Two contacts in series or parallel can perform either the "AND" ot "OR" function. It is simply a function of definitions.

When a closed contact means "TRUE", then two in series form an "AND" circuit,

When an open contact means "TRUE", then two in parallel form an "AND" circuit. I call this negative logic.

If I take any combination of switches (contacts) and form a network that ends up as just two terminals, then I get only one bit of output information, "TRUE" or "FALSE". There may be many different switch combinations that produce a "TRUE" or "FALSE" output, but there are only two output states.

In ptonsparky's case there is only one bit of useful information. This bit is OK to keep pump running, or stop pump. Can not be used to start or restart pump.

.

In most basic sense yes. With these systems we do find more ways to get some things done with just the three main power conductors and two control conductors, and some relays/contactors. With hydraulic driven pivot like OP has it's factory set up controls are often easy to use water pressure to start the system. I think there is only one manufacturer that makes those hydraulic systems all the others are driven by electric motors.
Those electric motor driven units factory controls are usually simpler to send a 120 volt signal to the well to tell it to run. If you have multiple systems controlling the well you usually just put in a control relay at the well for each system and then series or parallel the well control circuit through them. Automatic restarting is often done by cycling the power circuit to the pivot and having timing relays that initiate a start sequence when they are first energized. If the well and pivot are right next to one another we might run additional control wires between them to do whatwe want to do, but when the well and pivot are 1/2 mile apart a couple control relays at each end is less cost than more conductors over that half mile.