UK Continuity Relay

[tank]

Hi guys, I want to switch a 24 v load on using just the continuity of NO voltage free loop. Does anyone know of a relay or device or method that I could use to do this?
thanks

 

[pc1966]

What is the limit of voltage/current on the loop? Is it in use for another function?

Every device will have to apply some power to it, your choice comes down to how much.

 

[Darkwood]

You're query is a little ambiguous, can you expand on what you mean, in order to determine the continuity of a loop a voltage of some nature needs to be applied, can you expand on what the application is itself.
[automerge]1591687822[/automerge]
If you want an extra safe to use monitoring of the loop you can utilise a level relay often used to determine the level of a liquid, these usually use a reduced voltage of about 8v and the relay themselves offer a volts free relay output which you can use to drive other loads.

 

[tank]

You're query is a little ambiguous, can you expand on what you mean, in order to determine the continuity of a loop a voltage of some nature needs to be applied, can you expand on what the application is itself.
[automerge]1591687822[/automerge]
If you want a extra safe to use monitoring of the loop you can utilise a level relay often used to determine the level of a liquid, these usually use a reduced voltage of about 8v and the relay themselves offer a volts free relay output which you can use to drive other loads.

Hi, the application is of a flood sensing float switch which would in turn operate a 24v motorised valve cut off valve for the mains water.

The level relay you mentioning sounds promising. Do you think it would work for this application?

 

[Darkwood]

I assume the float is designed to give a N/O - N/C output, also if this is the design the connections will be suitably IP rated so using the 24v itself to monitor the float will be fine.

Be careful here when using floats, water tends to be turbulent and you do not want constant making and breaking of the float switch, ensure you use either a float with inbuilt compensation or an external monitoring that has integral time delay functions that can be set to ignore the water been a bit choppy.

There are many solutions for this out there, picking the correct one is down to you to research unless you want more guidance thus we need a lot more info about the job in hand and the nature of the water, where the float is sited and how you avoid nuisance cycling which would damage the relays and pump.

 

[tank]

I assume the float is designed to give a N/O - N/C output, also if this is the design the connections will be suitably IP rated so using the 24v itself to monitor the float will be fine.

Be careful here when using floats, water tends to be turbulent and you do not want constant making and breaking of the float switch, ensure you use either a float with inbuilt compensation of a external monitoring that has integral time delay functions that can be set to ignore the water been a bit choppy.

There are many solutions for this out there, picking the correct one is down to you to research unless you want more guidance thus we need a lot more info about the job in hand and the nature of the water, where the float is sited and how you avoid nuisance cycling which would damage the relays and pump.

Thanks for the reply. You have given me much needed information.

The float switch contraptions have been custom made and are fitted into the RC floors of the plant rooms of each level of an apartment block. ( The horse bolted after an almighty flood ). They have two flying leads for the switch coming out of the device which are connected in a near by adaptable box to cat5 cable which runs to the ground floor plant room where the cut off valve and power supply will be located.

I need to go have a good look at them with regards to IP rating and inbuilt compensation abilities. I suspect no such ability exists but I'll check.

I'm thinking a 24v boxed power supply with battery backup. A latching relay with push button release. All in a locked enclosure displaying warnings to depressurize the pumps before pressing the release button. (I'm assuming the valve is spring release. Will check)

Thanks again for the advice

 

[Darkwood]

As you feed info back it is starting to sound that this will warrant a specially designed control system which actively monitors the whole complex, also I suspect redundancy will be required for backup in case of failure of the primary detection system.
Given that a failure of the system could have costly consequences then you really do not want that falling back on your lap.

I suspect a fail safe system needs to be implemented here to ensure that if/when the time arises that it is needed it will be operational and reliable.

Yes I dare say one could throw in a very basic set-up that is functional but one must weigh up the cost of its failure to the customer and the cost to having a more expensive control and monitoring system in.

I have done similar systems in the past and where it is fitted to avoid a very expensive risk created by flooding then the control and set up has level monitors, back up pumps, alarm options and full test facilities inbuilt, ensure you know where your liability starts and stops here and also ensure the customer is aware of what you are offering and the limitations it may have which may be down to a budget for the job.
PS- always maintain a paper/E-trail to ensure you and the customer are in full knowledge of what is been supplied, they will be the first to contact you if it fails to work and may become a legal issue over insurance etc.
[automerge]1591703770[/automerge]
Hope I am not teaching you to suck eggs here, I just ensuring you are aware this may be a lot more complex in requirements than a basic functional monitoring relay set-up.

 

[tank]

As you feed info back it is starting to sound that this will warrant a specially designed control system which actively monitors the whole complex, also I suspect redundancy will be required for backup in case of failure of the primary detection system.
Given that a failure of the system could have costly consequences then you really do not want that falling back on your lap.

I suspect a fail safe system needs to be implemented here to ensure that if/when the time arises that it is needed it will be operational and reliable.

Yes I dare say one could throw in a very basic set-up that is functional but one must weigh up the cost of its failure to the customer and the cost to having a more expensive control and monitoring system in.

I have done similar systems in the past and where it is fitted to avoid a very expensive risk created by flooding then the control and set up has level monitors, back up pumps, alarm options and full test facilities inbuilt, ensure you know where your liability starts and stops here and also ensure the customer is aware of what you are offering and the limitations it may have which may be down to a budget for the job.
PS- always maintain a paper/E-trail to ensure you and the customer are in full knowledge of what is been supplied, they will be the first to contact you if it fails to work and may become a legal issue over insurance etc.
[automerge]1591703770[/automerge]
Hope I am not teaching you to suck eggs here, I just ensuring you are aware this may be a lot more complex in requirements than a basic functional monitoring relay set-up.

I have no problem with being taught how to suck eggs. If I need to be told, I'm grateful that someone is willing to tell me.
I am getting a little deja vu on your point about insurance and legal issues. Last year, I was warned off making a basic smoke vent controller by a fire officer after I suggested how I was going to make the system work. His reaction was a mixture of laughing and having a heart attack.

I'm currently waiting on details of the actuator, then I guess I'll persevere until I have a basic functional set up, then I'll talk the client out of using it.

What would my options be then? Would off the shelf devices exist that could do the job or may I need a engineering firm to make a panel for me?

thanks again

 

[Darkwood]

I cannot comment about off the shelf systems but wouldn't be surprised it a basic control did exist, the issue is that the variables of every job of this kind would make it hard to make a generic control that wasn't very basic so I would think it wouldn't have a big market.

As goes the smoke vent - I would tread very carefully here, this is a heavily regulated field and the liability of its design would be on your shoulders, unless you have an in-depth understanding of the surrounding regulations I would keep well away. If you need to fit a smoke vent under someone else's instruction then buy a complete control system, this will meet the operational and design aspects of the smoke vent and controls, you need to then liaise with the building control and fire officer and submit your plans on how the system works and how it is interconnected to any fire detection system in the building, the relevant regulations will guide you on this matter.

 

[Simon47]

In principle, all it needs is a circuit from one side of the 24V supply, through the switch, through the coil of a relay, and back to the supply. The relay then switches the load. If there's any doubt about how "cleanly" the float switch operates, then use a timer relay - a delay off will ride through off periods, a delay on will hold off until the switch is steady in the flooded position, and I'm fairly certain you can get delay on+delay off versions (will hold off until switch closed for set time, then hold on until the switch is open for set time).
Enhance with status lights, audible alarms, whatever as required.

 

[pc1966]

Another approach to the problem of clean switching is to have two sensors for hysterisis:

1. water low sensor to turn off
2. water high to turn on

So with the level below (1) the relay is latched off, then on exceeding (2) it is set on until it drops below (1) again. Another thing is if your float switches are change-over, you can sense if the circuit has gone open by a lack of both NC and NO showing continuity.

A timer that runs for X seconds after 'off' might be simpler!