Water Level Measurement

[Karam]

What’s often done in industrial situations is to use the pressure sensor to directly measure the head (height) of the water/liquid, rather than the pressure induced in the air space above it as this latter option requires a pressurized tank, or tube, as Karam points out.

I was implying measuring the head in an open not pressurized tank, i.e. the tube is just a convenient way to transmit the pressure at the bottom of the tank via the air pocket without, say, drilling into the bottom of the tank. But I admit I've not been in this sort of industry for quite a while. So I don't know if you can get an inexpensive transducer that can measure head directly coupled to the liquid?

As you say using an absolute sensor will probably be more than fine for such an application since atmospheric pressure probably varies by no more than 2-3%. But it seemed to make sense to avoid this when differential transducers appeared as inexpensive as the absolute ones.

[TimH]

I was implying measuring the head in an open not pressurized tank, i.e. the tube is just a convenient way to transmit the pressure at the bottom of the tank via the air pocket without, say, drilling into the bottom of the tank.

Sorry Karam, I don't think I explained it very well but I think we're saying the same thing. The air pocket at the top of the tube negates having to pressurise the whole tank.

Cheers,

Tim.

[Karam]

Tim,

Ah yes I understand. Do you know of alternative pressure transducers which are more popular for this sort of thing? Years ago I was doing some water level control and we did at the time use silicon type air pressure sensors with an external tube connecting them to an aperture at the bottom of the tank. It seemed to work fine over a fair period of time but then the tank environment was not particularly challenging.

On other technologies: We do know of one customer who's been measuring fuel oil level for some years now using an industrial ultrasound sensor connected to our system via the QAI (and a resistor to convert from 4-20mA). It works ok but the sensor was not so cheap. I think as you describe it guided the ultrasound through a short tube which has got to be a good idea to reduce any side reflections from tank walls. Could be that a makeshift tube might help the Maxbotix device?

[pdwarriner]

I did some work years back measuring air pressure on respiratory products and found http://www.sensortechnics.com had an excellent range of laser calibrated sensors.

Most sensors have different output options as well.

Peter.

[Karam]

Peter,

Indeed, and that answers my above question - they have a bunch of directly wetted sensors as well.

[TimH]

Tim,

Ah yes I understand. Do you know of alternative pressure transducers which are more popular for this sort of thing? Years ago I was doing some water level control and we did at the time use silicon type air pressure sensors with an external tube connecting them to an aperture at the bottom of the tank. It seemed to work fine over a fair period of time but then the tank environment was not particularly challenging.

My experience is largely with the industrial pressure sensors, so Rosemount/Emerson would be my first port of call (2-wire, 4-20mA) but bulky for home use. I did get involved with Druck sensors for a particularly low cost project, although that was "low cost" by industrial standards, not necessarily "hobby" low cost...

From what I recall, and using this guide as an aide memoire (http://www.davidson.com.au/products/...iter-guide.pdf) we used the fixed-range "PTX 1400" models. These also use the standard 2-wire, 4-20mA interface (we were going into a PLC).

On other technologies: We do know of one customer who's been measuring fuel oil level for some years now using an industrial ultrasound sensor connected to our system via the QAI (and a resistor to convert from 4-20mA). It works ok but the sensor was not so cheap. I think as you describe it guided the ultrasound through a short tube which has got to be a good idea to reduce any side reflections from tank walls. Could be that a makeshift tube might help the Maxbotix device?

You could (re)confirm with the Watchman people, but someone on the Yahoo Selfbuild list has been using a Watchman sensor on their water tank (spring water). I'm not sure how you would interface that to an HA system as it reports via RF directly to its own display, but presumably it would be possible. The Watchman is an ultrasonic device.
More info here: http://www.sensor-systems.com/produc...ion.html#Sonic Prices typically are <£100

Or there's this from Velleman:
http://www.vellemanusa.com/us/enu/pr...iew/?id=350507
and/or this http://www.amazon.com/VELLEMAN-WATER.../dp/B0002Z82O4
and replace the buzzer with a relay, then the dry contact (sorry, no pun intended...) goes into the AH system

HTH,

Tim.

[Aristoteles]

I wonder if we could get a follow up from Paul on this. Did you install it and if so how did it work?
I want to do the same think, but I am a bit suspicious about the reliability of the ultrasonic distance meters. The MaxBotic cost ap 25 EUR and seems to be unreliable? Comparing with a more industrial grade like VEGA which seems to cost ap 1000EUR.
/Glenn

[chris_j_hunter]

in the event, we used a number of these to measure water-level :

http://www.rapidonline.com/electroni...rtical-61-1315

connected to an ODI & to digital inputs of convenient other modules ...

works well ...

an alternative we considered was :

http://gillsc.com/content/level.htm

which might have been better (more detail) ...

Chris

[Paul_B]

I wonder if we could get a follow up from Paul on this. Did you install it and if so how did it work?
I want to do the same think, but I am a bit suspicious about the reliability of the ultrasonic distance meters. The MaxBotic cost ap 25 EUR and seems to be unreliable? Comparing with a more industrial grade like VEGA which seems to cost ap 1000EUR.
/Glenn

Glenn,

I never got this working. My initial trial seemed to have problems with the signal bouncing off the sides of the tank. I did purchase a newer model that has a tighter beam but never got round to testing it.

Chris, your float switch looks great have you got anymore pics details as to how you configured and on what devices?

Paul

[chris_j_hunter]

Paul -

photo's attached - they were wired back to an ODI module, but digital inputs on any module would have done equally well ... we then defined a Group for Viewing them Historically, and created some Connections for spoken alerts & LED signalling ...

two float switches are installed inverted (one vertical, one inclined), the rest are right-way up - all work fine ...

all metalwork was galvanised, with cut edges painted to make good (galvanising paint) ...

May'12.jpg

HTH

Chris