Water level sensor

[megatron]

Hello everyone
I am going to try and build a boiler control system which will sense the pressure and the water level and control the gas burner and feed pump. The problem is I have no idea how to detect the water level. I have seen sensors attached to the sight glass which is the type I would prefer to make. Does anyone know how these sensors work and what components they use?
Thanks

[steamboatmodel]

This was posted on RC Groups,
"The book "Scale Model Ship Propulsion", by Tom Gorman, shows an electronic gas pressure regulation system which uses both a water level sensor and a boiler pressure sensor. The water level sensor is an optical device which clamps to the glass tube of the water level sight gage. The system was available from Cheddar Models Ltd.," http://www.rcgroups.com/forums/showthread.php?t=1384622
Regards,
Gerald.

[megatron]

Thanks for reply  steamboatmodel,
I have a model fitted with a cheddar ABC system but I was wanting to design one myself that uses off the shelf components which is cheap to make and doesn't involve programming microprocessors. The Cheddar water sensor is fairly simple with only 4 components but I haven't been able to identify what these components are. Controlling the pressure should be fairly easy to do as it only involves measuring the temperature and I have built thermostats before for my homebrew boiler.
I would love to hear from anyone who has built or is building one of these systems.
Stew

[R.G.Y.]

If you are sucsessful please post it. I would like one. Geoff

[john s]

I understand that the actual sensor used. Is of the type used on commercial coffee machines. I could be wrong. If you wish please pm me your phone number as i think i can help you more. John.

[R.G.Y.]

John .That is a very good lead. I will be having word with my son. He contracts to a major super market chain. (refrigeration & electronics) Geoff

[steamboatmodel]

Be sure to report your findings on here.
Regards,
Gerald.

[megatron]

I understand that the actual sensor used. Is of the type used on commercial coffee machines. I could be wrong. If you wish please pm me your phone number as i think i can help you more. John.

I've sent you a PM
megatron

[rayspan]

Have just constructed such a system, hoping to test it tomorrow. It's based on the system shown in Stan Bray's book, 'Model Marine Steam.' It's attributed to Roy Amesbury.  I've made my sensors like his, a brass bush containing a bronze electrode in a teflon sleeve.

I've measured the sensor resistances, wet and dry, in order to develop my own circuit. This uses a couple of dual op-amps, LM358N. I got mine on ebay, pack of 5 for about six quid. Much simpler to make.

I've put the finishing touches to it only a couple of hours ago, and operated it with a 1K-ohm resistor to simulate the sensors. It seems OK. I'm knackered this evening, working in brass monkey conditions in my shed! Otherwise I'd have done a pukka trial already.

Spent the earlier part of the day silver soldering a couple of minor leaks in my boiler, and pickling it to clean the grot off, so am in good shape to put it all together tomorrow . . . in our nice warm kitchen!

I'll let you know how I get on. If it works I'm happy to share the details with the forum if anyone's interested.

[megatron]

Hi Rayspan, what resistance did you get for the sensor, 1K seems very low?
Are you going to use this to operate a servo or just light an Led?
I've just about finished my design which controls the boiler level and gas supply and monitors tank level. I've built an optical sensor to detect the water in the sightglass but don't know how reliable it will be. A sensor like the one you've built will be more reliable but it means altering the boiler.
Stew

[rayspan]

Hi again megatron. Good question! Thereby hangs a tale!

First thing I did after making sensors was to measure resistance for each, both wet & dry. Findings were:

Dry - greater than 10 Megohms. Wet - less than 1 K-ohm. I also noticed that the wet resistance reading was steadily, and very slowly, falling to 800 ohms and less.

I decided it was a typically galvanic type of action, in mains water which probably has a non-neutral pH value.
Checking the article attached, I found brass copper and bronze are all next to one another in the galvanic table,
just above stainless steel, so why worry?

Fair enough, I designed my circuit and simulated the wet probe with a 1K-ohm resistor. Circuit switched nicely
so attached it to boiler electrodes and met total failure!

Puzzled, I repeated resistance measurement again and was horrified to find wet resistance over 3K and steadily increasing.

Intuition nudged me to reverse the probes of the resistance meter, to find a reassuring 800 ohms, falling steadily once more. I convinced myself by rechecking several times with consistent results.

I'd built my circuit assuming the same orientation Roy Amesbury shows in his circuit, !.E. bronze cathode, copper anode. The conclusion was it should be the other way around. A few quick flicks of the soldering iron
and I swapped the probe ends. This time - SUCCESS.

I've just coaxed my lady wife to operate the rig with a jug of water while I videoed it. Should be available on you tube tomorrow somewhen. I'll post its URL when that happens.

Circuit attached. I'd be glad of comments, critical or otherwise!

[rayspan]

P.S. I'm hoping to cobble up a feed pump driven by an electric motor. I have several high torque devices from my aeromodelling days. Just wondering how powerful it would have to be to inject feed water into boiler at say 60P.S.I.

If anyone can suggest a way of doing it like that, I'd be glad to hear from you.

[megatron]

Hi Ray,
there's a chart on this website to calculate power needed for water pump.
http://www.engineeringtoolbox.com/pumping-water-horsepower-d_753.html
Looks like 0.03hp to pump 1gallon per minute at a head of 125ft which I think is about 60psi, you don't need anywhere near 1gallon/min so you're not talking about a very big pump at all. I'm sure I've read about people using car windscreen washer pumps but you would need a 12v battery. Could you not build a pump to be driven from your crankshaft?
Have you read Malcolm Beaks article in the downloads section, Water level control?
Stew

[rayspan]

Many thanks megatron, all looks right on target. Numbers are encouraging too, I quite fancy devising a neat little reciprocating pump to operate in the ranges indicated.

Yes, I  like the idea of pumping with crankshaft. Maybe it's my  ignorance, but what happens to boiler pressure when you start injecting cold water into an almost empty boiler? Surely, pressure will drop until it gets up steam again. In which case there won't be any power o/p to drive the pump will there?

12v isn't a problem, I still have several battery packs and requisite chargers from aeronautical days. Weight shouldn't be a problem either, I used to fly these things, so floating should be a doddle - compared to steam plant and engine anyway.

Water source is something else, if I can't just pump it up over the side, it will have to be stored on board. I should think outdoors water in a lake for instance, would be less inclined to scale up steam plant than mains tap water. I know rainwater is recommended, but there is so much pollution in the atmosphere it's difficult to weigh pro's over con's.

Advice please all you steam engineers out there?

I forgot to mention the LED's I used in my circuit. They are the big, 'superbright' ones, operating around 20mA. Should be easily visible from the bank with binoculars if not naked eye.

[rayspan]

I've just checked youtube, seems to be up & running.

http://www.youtube.com/watch?v=hhDXCVXVZyg