# New help using 2 floats switches on Feed water tank



## splatz (May 23, 2015)

Usually it's better to buy a pump controller but it would just be a latching relay circuit

The NO contacts on the lower float go where "push to make" is, and the NC contacts on the upper float go where "push to break" is. The pump would be switched on with the C-D contacts. 

But then you'll want an HOA switch as well... a low alarm and a high alarm and possibly shutoff... maybe a second pump for redundancy, and you'll want to alternate lead / lag ... and you wind up buying a pump controller. 


http://www.reuk.co.uk/OtherImages/make-latching-relay-with-a-dpst-relay.jpg


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## jw0445 (Oct 9, 2009)

splatz said:


> Usually it's better to buy a pump controller but it would just be a latching relay circuit
> 
> The NO contacts on the lower float go where "push to make" is, and the NC contacts on the upper float go where "push to break" is. The pump would be switched on with the C-D contacts.
> 
> ...


You just blew his mind....


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## 3DDesign (Oct 25, 2014)

Is there an alarm with the controls?


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## micromind (Aug 11, 2007)

If you understand motor controls, connect the bottom float as a start button and the upper one as a stop button and think of the valve coil as a starter coil.


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## frenchelectrican (Mar 15, 2007)

micromind said:


> If you understand motor controls, connect the bottom float as a start button and the upper one as a stop button and think of the valve coil as a starter coil.


To OP just read what Micromind saying and he got right to the point very hard and fast.,


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## John Valdes (May 17, 2007)

I wish some of us older guys had a forum to go to for answers. We had to figure it out ourselves or get help from co-workers.
Its just to damn easy today and I expect many of young guys will benefit in the short term and be lost in the long.

OP. Take out paper and pencil and find a stop start drawing on the internet.
Print it out and change it to suit your needs.
Then take that to the project and make it work.

I bet you might even find one made just for your application. Online.
You will never be more than an installer until you take the time to figure out how stuff works.


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## LGLS (Nov 10, 2007)

The OP sounds more like a homework question.


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## paulengr (Oct 8, 2017)

3DDesign said:


> Is there an alarm with the controls?


We have 2 floats and so 4 possible states:
Below both floats, above both floats, between both floats, and a 4th one where the bottom float indicates low and the top float indicates high.

That last one would be a fault condition (bad float).

To get an alarm you need to either add floats or assume one of the valid conditions is an alarm state. Typically you will see either "hi hi" or "low low" alarm or both floats just outside the high and low float range. These go straight to the alarm.

Or you can use a single analog (4-20 mA) level transducer and a pump controller and do away with all the floats and optionally keep just one if the analog stuff fails.


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## Cow (Jan 16, 2008)

CharlieWheeling said:


> I'm trying to wire a feed water tank. It has 2 floats. I want the bottom float to open my valve when it goes below, then fill to my higher limit float. Anyone know how to wire that off the top off their head?


Floats? That's too easy.

Let's put a Click PLC on it with a pressure transducer. Transducers last longer than floats...if you order them right.


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## sparkiez (Aug 1, 2015)

:vs_cool:

Challenge Accepted:

A The E-Stop cuts power to the entire system, which you probably don't need R1, which is just a power control relay.

The Hand setting energizes the pump/valve relay M1
The auto setting feeds the low level NC float switch F1 that will close when the water drops to a certain level, then to the NC upper level float switch F2.

F1 and F2 will both be closed and will feed the M1 relay, which has a NO set of auxiliary contacts, which close and bypass float switch F1 as the tank is filling. Once the upper level limit is met, the float switch opens and breaks the latching circuit.

Note that this is only for filling a tank, not controlling something such as a collection pit.


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## splatz (May 23, 2015)

Cow said:


> Transducers last longer than floats...if you order them right.


 @Cow, tell us more - how do you get transducers to last longer than floats?


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## sparkiez (Aug 1, 2015)

I see you are opening a valve, so for that circuit instead of a motor starter you would use an 8-Pin ice cube with 2 sets of NO contacts. One set of NO contacts will act as the auxiliary contacts and the other will energize your valve.


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## splatz (May 23, 2015)

sparkiez said:


> I see you are opening a valve, so for that circuit instead of a motor starter you would use an 8-Pin ice cube with 2 sets of NO contacts. One set of NO contacts will act as the auxiliary contacts and the other will energize your valve.


Huh I didn't notice it was a fill valve not a pump but opening the valve and running the pump would do the same thing, so it's all the same from a wiring perspective.


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## paulengr (Oct 8, 2017)

splatz said:


> @Cow, tell us more - how do you get transducers to last longer than floats?


Easy. Key to pressure transducers is they have a very tiny 1/8" or so opening that is both fragile and easily clogged. Use a good chemical diaphragm seal that flush mounts to go after it directly.

Or use a bubbler for the tried and true wastewater approach. Use a small aquarium fish pump (or two for redundancy) to pump a small amount of air into a tee. The other two ends of the tee are the pressure transducer and the bottom of the tank. The transducer and air pumps are outside the tank. Usually everything is Tygon tubing and barb adapters. The air in the line is often adjusted with a needle valve because you just want a bubble once in a while. The bubbles flush the line out. The pressure on the air if the flow is slow (much less than 1 CFM) is equal to the water pressure at the mouth of the tube in the bottom of the tank.

A variation on this or the direct approach handles density. Add a second probe at a fixed height from the first. The pressure difference is proportional to density.

Or skip that and use an ultrasonic level transducer such as Hyde Park which is now owned through Schneider but most of the better transducers are still sold through the Hyde park distribution channel last I knew. Or use guided wave or unguided wave radar for truly difficult systems like foam or sludge...works when nothing else does but very, very expensive.

There are also "mud divers" or "yoyos" that use a bob on a cable reel that periodically reel out to "stick" the tank. Seems simple but they are a constant maintenance headache.

Also I've seen using an infrared camera to measure tank level. Works well as long as the tank level changes slowly enough and there is a temperature difference. It's more useful for a plant where manually "sticking" the tank is required and saves time climbing the tank every time.

Either way the signal for all of these is a 2, 3, or 4 wire 4-20 mA system, either self excited or loop powered. The PLC input (Click is a cheap and decent Toyo one from Automation Direct) converts it to a digital number. In the PLC this represents a level as a percent but can be converted to feet or inches with simple math. Then simple compare logic triggers PLC Code that controls a relay output just like the wiring or it can even control another 4-20 mA output that can control an electric control valve or a VFD driving pump speed for instance.

Either way I just described 99% of the automation in a wastewater plant. The real key in those things is using transducers that outlast floats, with redundancy and backups, while dealing with whatever people try to flush down a toilet, and being to be able to maintain it while not getting exposed to either sewer gas or possible infectious disease in the water. When it comes to nasty environments, those guys know what works and what doesn't. They're some of my customers. 

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## splatz (May 23, 2015)

Thanks Paul, that's some food for thought. I have one that gives me trouble, it's at the bottom of a retention pond that's part of a convoluted stormwater handling system. The site is unmanned but the level measurement is critical. The pond presents some challenges. There's nothing over the pond to hang an ultrasonic sensor or floats. However site safety rules prohibit getting in the pond to place the transducer, and obviously you can't fill or drain it on demand. The water is never transparent enough to see more than a couple inches below the surface. So getting the transducer in place and calibrated is a challenge. 

I'd like to set posts at opposite sides of the pond, run a strand between them, and hang floats off there. Floats IME are not super reliable, I regularly find floats that no longer open and close properly, but I suspect that upgrading to better brand floats would help, and even the good ones are cheap enough to double up for redundancy. 

I'd also like to experiment with the PLC, connecting both the NO and NC contacts of SPDT float and defining an alarm condition if the NC contacts open and the NC contacts don't close within a second, or vice versa. Likewise an alarm if both are open or both are closed at any time. I have not tested this, but I suspect that would reliably detect a float that is no longer opening and closing properly.


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## Cow (Jan 16, 2008)

I use a fair amount of floats Splatz. 

I have the best luck with the floats that rattle when you shake them, like an aerosol spray paint can. I've been using the SJE-Rhombus ones from Grainger the most lately, since they're readily available. I can usually get 2-3 years out of them in water tanks, but only maybe a year out of them when they're in manure pits constantly get bounced around by agitators. I don't use them in ponds or pits around here without agitation, we learned a long time ago floats don't work well when they freeze into the surface of what you're trying to measure.


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## splatz (May 23, 2015)

Thanks Cow, we'll have to try the SJE-Rhombus, I have not tried those. 



Cow said:


> we learned a long time ago floats don't work well when they freeze into the surface of what you're trying to measure.


That part might prevent us from using anything but a trasnducer, in my opinion it isn't necessary since the pond is generally empty all winter but the way things are run at that site, it might take a lot of red tape to get the OK to only monitor in above-freezing conditions.


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## sparkiez (Aug 1, 2015)

splatz said:


> Thanks Cow, we'll have to try the SJE-Rhombus, I have not tried those.
> 
> 
> 
> That part might prevent us from using anything but a trasnducer, in my opinion it isn't necessary since the pond is generally empty all winter but the way things are run at that site, it might take a lot of red tape to get the OK to only monitor in above-freezing conditions.


Another option to consider is to set a pipe with an ultrasonic sensor at the top. You put a hole in the bottom to allow water to enter and have it capped so there is no issue with rain entering.


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## Rora (Jan 31, 2017)

Instrument tech here, would have to agree with using ultrasonic on a stilling well as sparkies described, simply because nothing else will fit your criteria and its main limitation (foaming) shouldn't be a problem. Would be relatively easy to install... encase the bottom of a stilling well in concrete and drop it in, transmitter would be safe and secure at the top.

- A bubbler system would be the next best option, and this is a common solution for level measurement in dirty processes. However, it introduces more points of failure which is a concern for an unmanned location. Not exempt from needing a place to mount everything, either.

- Differential pressure would not be ideal since you don't have external access to the bottom of the pond. Submerging the transmitter is possible, but it's very uncommon in the industry. Wouldn't recommend it, would require robust ingress protection and the serviceability would be terrible.

- Guided-wave radar could be anchored from above the surface, but would still require some way to mount the top end. The real reason this wouldn't work is the accuracy suffers from residue, which would inevitably form on the wire in an application like this.

- Floats suffer from physical wear-and-tear and only really offer point detection, not to mention the freezing issue that was mentioned.


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## splatz (May 23, 2015)

sparkiez said:


> Another option to consider is to set a pipe with an ultrasonic sensor at the top. You put a hole in the bottom to allow water to enter and have it capped so there is no issue with rain entering.





Rora said:


> Instrument tech here, would have to agree with using ultrasonic on a stilling well as sparkies described, simply because nothing else will fit your criteria and its main limitation (foaming) shouldn't be a problem. Would be relatively easy to install... encase the bottom of a stilling well in concrete and drop it in, transmitter would be safe and secure at the top.


Setting it at the top of a 4" pipe ought to work great. I could paint depth marks on the pipe for a low tech HMI depth reading  That will help set the scale when it's in place. I'll set the pipe in a plastic tub full of concrete that we can safely skid into place. 

Excellent idea. Thanks!


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## paulengr (Oct 8, 2017)

Guided wave triggers on the strength of the change in RF impedance which causes a strong reflection. Dirt/dust buildup on the cable won’t do it. That’s why it can be set up to ignore foam (weak reflection) and pick up the strong reflection on a liquid surface or look from one “direction” or the other such as looking for the last strong reflection so from the bottom rather than the top or vice versa to find the top of the foam.

Guided wave works decent when nothing else does. But it’s expensive. I think the last one I bought was close to $5k and I don’t expect the price to come down soon.


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## Rora (Jan 31, 2017)

splatz said:


> Setting it at the top of a 4" pipe ought to work great. I could paint depth marks on the pipe for a low tech HMI depth reading  That will help set the scale when it's in place. I'll set the pipe in a plastic tub full of concrete that we can safely skid into place.
> 
> Excellent idea. Thanks!


As sparkies mentioned, the stilling well needs a hole at the bottom. Wanted to mention that a hole above the maximum height of the fluid so the air isn't trapped is also necessary, typically they're closer to the top/transmitter.

Be sure the transmitter is spec'd properly. There are many different types of dishes, you'll want one that is designed to be mounted on a stilling well and choose the size of the well based on that. It should be mounted a certain distance above the maximum level to prevent ringing, i.e. they have a minimum measurement distance which will be part of the spec.

Something else to consider is corrosion and biological build-up, the inside of the well needs to be nice and smooth to prevent false echos. Treated PVC is a good option. If the accuracy starts to suffer the well may need to be cleaned, so serviceability is something else to think about when mounting the transmitter.



paulengr said:


> Guided wave triggers on the strength of the change in RF impedance which causes a strong reflection. Dirt/dust buildup on the cable won’t do it. That’s why it can be set up to ignore foam (weak reflection) and pick up the strong reflection on a liquid surface or look from one “direction” or the other such as looking for the last strong reflection so from the bottom rather than the top or vice versa to find the top of the foam.


Any high dielectric buildup is known to affect the accuracy, but yes modern systems can probably overcome this algorithmically. As you say, for a price...


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## splatz (May 23, 2015)

Rora said:


> As sparkies mentioned, the stilling well needs a hole at the bottom. Wanted to mention that a hole above the maximum height of the fluid so the air isn't trapped is also necessary, typically they're closer to the top/transmitter.


I kind of pictured drilling holes in the PVC like they do with the flexiblepipe for french drains...



> Something else to consider is corrosion and biological build-up, the inside of the well needs to be nice and smooth to prevent false echos. Treated PVC is a good option. If the accuracy starts to suffer the well may need to be cleaned, so serviceability is something else to think about when mounting the transmitter.


That would be a major consideration. They have an excellent maintenance plan at this site on paper, not so hot in actual maintenance. Things tend to scummy up real fast. 

I was thinking about embedding a rigid stub in the concrete on the bottom and coupling to PVC so it can be replaced easily ... realistically replacing it once a year is more likely to actually occur than cleaning it once a year. 

What happens if the minimum distance is exceeded, do you get some kind of out-of-range reading or an inaccurate reading? I could deal with out of range, just treat it as an alarm, but I would not want to risk an inaccurate reading, it has to be reliable.


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## Rora (Jan 31, 2017)

splatz said:


> What happens if the minimum distance is exceeded, do you get some kind of out-of-range reading or an inaccurate reading? I could deal with out of range, just treat it as an alarm, but I would not want to risk an inaccurate reading, it has to be reliable.


The issue is that the emitter has to have enough time to stop vibrating after sending a wave before it can begin to try to detect the echo, during which it ignores its reading (since it would only pick up its own vibration). The wave has to travel a certain distance (the blanking distance) and back while this time elapses. I haven't encountered a system that doesn't detect ringing, I'd imagine it does this by picking up the echo in addition to its own vibration before the necessary time has elapsed.

May want to check out Emerson's resource, specifically section 6.10 and section 7, which also talks about temperature compensation (sound travels at different speeds depending on the temperature). I'm sure there are probably other guides out there regarding the subject.

http://www.emerson.com/documents/au...o-Level-Measurement-2013-EDITION-en-77708.pdf


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## RePhase277 (Feb 5, 2008)

The OP said feed water, which makes me think boiler, but hell, could mean a horse trough. For simplicity, accessibility, and longevity, why not a diaphragm switch and tube, like a washing machine?

PLCs and electronic transducers have their place, but if all you want to do is keep a tank of clean water filled, it's my opinion that anything more than a mechanical switch is unnecessarily adding potential failure points that serve no purpose.


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## emtnut (Mar 1, 2015)

RePhase277 said:


> The OP said feed water, which makes me think boiler, but hell, could mean a horse trough. For simplicity, accessibility, and longevity, why not a diaphragm switch and tube, like a washing machine?
> 
> PLCs and electronic transducers have their place, but if all you want to do is keep a tank of clean water filled, it's my opinion that anything more than a mechanical switch is unnecessarily adding potential failure points that serve no purpose.


I agree. And from my experience, a 'blue ball' has proven to be the most reliable high level/overflow alarm I've ever used.

p.s. I see your new here ... Welcome to ET @RePhase277 :thumbsup:


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## paulengr (Oct 8, 2017)

Ultrasonic level sensors are both a "transmitter" and a "receiver". The transducer is a piece of piezoelectric crystal...put an AC signal on it and it vibrates. Treat it like a microphone (vibrate it) and it generates an electrical signal. Simple and cheap. The minimum distance (blanking interval) is how long it takes to switch from transmitter to receiver. If the level is inside that range, it gives you an error (no echo), identical to an empty tank even though it is full. The voltage level when transmitting totally washes out the very tiny signal that it makes when receiving so from a practical point of view the only way to transmit and receive simultaneously would be with two different transducers. That is done with some flow meters but not with level sensors.


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