Liquid Level Sensor
Liquid Level Sensor
(OP)
Hello everyone.
I am trying to figure out a way to monitor the level of liquid in a large fixed container and output that information (via serial, USB, Cat5, etc.) to a program on a windows machine to display the current levels.
I have been looking at different "off the shelves fuel lever sensors" that will probably work to measure the level of fluid, but I am unsure how to take that signal and convert it to something that is readable on a users PC.
Any suggestions would be greatly appreciated.
I am trying to figure out a way to monitor the level of liquid in a large fixed container and output that information (via serial, USB, Cat5, etc.) to a program on a windows machine to display the current levels.
I have been looking at different "off the shelves fuel lever sensors" that will probably work to measure the level of fluid, but I am unsure how to take that signal and convert it to something that is readable on a users PC.
Any suggestions would be greatly appreciated.





RE: Liquid Level Sensor
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Liquid Level Sensor
RE: Liquid Level Sensor
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Liquid Level Sensor
Are there other characteristics of the fuel, besides flammability, that need to be considered? Corrosive, erosive, nasty, sticky, gooey, a fume generator or foamy?
And you should be aware that the selection of level instrumentaion is governed in large part by available access to the tank. Access from the top? from the side? from the bottom? There are serious considerations to poking holes and welding fittings into tanks and vessels, particularly fuel tanks.
Another consideration is how close the tank is to where you want the data. Industrial level sensors typically use a 4-20mA analog signal that can travel a mile through copper wire, but RS-232 has what, a 50'-60' limitation?
There are converter modules that will convert anaalog 4-20mA to serial or any of several industrial protocols, like Modbus,which is a serial protocol that runs on RS-232, RS-485, and nowadays, I suppose Modbus TCP on ethernet. Google: "converters 4-20ma to serial" for numerous options.
Dan
RE: Liquid Level Sensor
I have software engineers that can design the program I need, I just need to get the data to them.
RE: Liquid Level Sensor
RE: Liquid Level Sensor
You can google bubbler "level sensor" type level sensors, and see if they will point you in the right direction. Downsides, they need a source of air (not usually a problem in industrial settings.) Wikipedia has a write up on it.
Continuing on the downside, the signal output is based upon the specific gravity of the fluid measured. Downside again, if you want to build your own, you will need to interface to a pressure transducer and you are back to where you started from. Doing the level conversion, a/d and the associated work can be done. There are lines of a/d pressure transducers that are inexpensive that do the conversion for you, then it's a "simple" matter to use the stamp to read the a/d, do whatever
conversions you deem necessary and send it to a pc via your serial interface.
On the upside, bubblers are pneumatically coupled to the tank so that you might find that they work quite well in "hazardous" conditions, inherently have the sensor divorced from the fluid in question and can have a "bypass cleaning" air circuit to clear the tube from deposits or solids caught in the tube while not in operation.
The pc can track the levels looking for alarm limits or store the information on the levels in some sort of a data base or flat file. Display can be via whatever. For this application, I would look at the free "RRD" at:
http://oss.oetiker.ch/rrdtool/
but that's me personally. RRD will allow one to display via
a web interface graphs assoicated with the level, rate of change of the level, limits or whatever is of interest as long as it's configured correctly.
Watch the filtering of the a/d of choice and of course building the sending unit in a robust enclosure. You can scale the levels (although in this application, a barrel is not too deep, to a variety of measured depths, by proper choice of pressure transducers). A small needle valve is usually sufficient for setting the air pressure which should be enough to "bubble" air through the bottom of the sensing tube with the liquid of choice at it's highest level.
I hope that this helps in your efforts in solving the problem at hand.
Cheers,
Rich S.
RE: Liquid Level Sensor
RE: Liquid Level Sensor
http://www.sensor-systems.com
..they do this and the website can give some ideas.
RE: Liquid Level Sensor
You can try the following ultrasonic-based level sensors. They are all expensive, starts from $250 or so. Their usual output is 4-20mA current loop. However, all of them offer digital data links (RS232, RS485) with very small added price. Check them. By the way, you can forget about USB.
www.senix.com
Select model TS-15S-SR232 or TS-15S-485
www.automatedsonix.com
Select model Sonix-40 and request for RS232 output
www.ssitechnologies.com
Their accutrac product line has default RS485 port.
www.migatron.com
I have not used their product, but ask them if they have serial output sensors.
Regards
YR
RE: Liquid Level Sensor
RE: Liquid Level Sensor
You *MIGHT* be able to do it for about $20.00. But just barely. If you are not doing 100s of these, then you shouldn't.
Wandering through the Jameco catalog I ran across this sensor:
Pn 218827CC pro nu mpx 10gs $8.99 each Motorola 0 - 1.45 PS
Assume that you can find a wall wart type transformer surplus for about $3.00, and you will need a 3 terminal +5V regulator. Depending upon the op amp of choice you might do as I did and have +12V for the op amp for level overhead on the device.
Now you will also need some amplification, say a quad op amp with suitable filtration, about a dozen 1% resistors and about 3 to 5 caps (some of them zero term. stable). I've done a 3 amp design using the old LM357s and can get away with about $5.00 of parts. This is where the +12V came into play.
A PIC 12F675 will do for the A/D converter and converting to an RS232C type interface. A Maxim RS232 converter for another $3.00 or so. Oh, the PIC is about $3.00.
So, that's a grand total of about $24.00. IF you are willing to perf board the project I would assume 0.00 for the board.
Now, comes the hard part.
Design. When I did my design, I looked at hundreds of hours of design investment. Added to this, the development system for the PIC runs $150.00 for an ICD2 or knock off, and another $35.00 or so for the "header" board for the development system to interconnect in place of the PIC. You *COULD* debug without the ICD2, but expect to spend another 100 hrs or so for the additional time spent without it.
My purpose was to come up with a working design using the LM357 op amps and to have an off the shelf "insturmentation" amplifier.
I also hand fabbed my own circuit board.
I figure that I have about 200 hrs of effort into it. This is including the "bit bang" RS232 interface which was leveraged from another project.
So, for example, if you found an utrasonic interface for $250.00 (I couldn't find a price list on the above mentioned web pages) vs. the intention of building your own, that works out to:
$250.00(per unit)/200(hrs. development time) works out to $1.25/hr.
I sure hope that you make more than that!
My criteria is different. For me it's both an advocation (hobby) and a vocation. It was an interesting case study, and a valuable set of tools (some of which were built from other designs). It has NO CERTIFICATION, IS NOT UL NOR FCC approved, and although "safe" in design with the low voltage, isolated supply, would have all sorts of inspectors waving all sorts of red flags if not properly done.
This might be a fun little project to include in a hobby magazine and might show up in a future issue. *BUT* don't think that the proceeds would add materially to your finances. It doesn't!
So, although you might be able to do it for $20.00 or so, the time invested, would most likely preclude you from going this path.
If, OTOH, this is something that you desire to learn more about and wish to persue the DIY (do it yourself) route, these tips might help you along your path.
Cheers,
Rich S.
RE: Liquid Level Sensor
So, if you read the count and reset the counter every second, for example, you should be able to see the count go up and down with the liquid level. This solution is about as simple as it gets. You might be able to get your rate up to $2 or $3 per hour!
Jason
RE: Liquid Level Sensor
Regarding the computer interface I do want to mention the Velleman K8055 USB interface board which is very simple to use and very cheap. I have used it and works fine.
ht
CODE
5 digital inputs (0= ground, 1= open) (on board test buttons provided)
2 analogue inputs with attenuation and amplification option (internal test +5V provided)
8 digital open collector output switches (max. 50V/100mA) (on board LED indication)
2 analogue outputs:
0 to 5V, output resistance 1K5
PWM 0 to 100% open collector outputs max 100mA / 40V (on board LED indication)
general conversion time: 20ms per command
power supply through USB: approx. 70mA
diagnostic software with DLL included
dimensions: 145 x 88 x 20mm (5.7" x 3." x 0.8")