# Submersible pressure transducer?

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Thread Starter

#### Jacob

I'm looking for a cheapish and rugged pressure transducer for measuring the water level in a river. What I have in mind is a length of protective PVC drainpipe strapped to a bridge pillar with the sensor at the bottom of it. But I'm baffled by the range of sensors offered, and a little unimpressed by prices. Can anyone recommend a particular product? Thanks! I've looked at resistance tape and similar solutions, but they seem to be even more pricey...

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#### David Corking

I can't recommend anything but humbly offer some self-help suggestions. Ask yourself some questions about your application before you contact one or two local instrumentation distributors. Such as: 1)what kind of signal do I want from my transducer - wireless, 4-20ma, RS232 ? 2)will my budget allow for professional installation, waterproof wiring ...? 3)where do I want my display/output? 4)do I have a supply of power and compressed air? 5)how reliable should it be? 6)do I want it to work when it has dried out or should it also work when wet (storm conditions)? 7)how often can someone maintain/clean it? ... I guess you want to use pressure to minimise cost. AFAIK the lowest cost "differential pressure" level instruments are not submerged. Instead a gas-filled impulse line (metal tubing with a flow of compressed air) extends from the instrument deep under the surface (instrument text books show this.) River specialists have other tricks which I am not familiar with. Here is an interesting web link http://www.srh.noaa.gov/lmrfc/education/fcstmethods.shtml#data There are many variations many of which should be inexpensive if you want to sacrifice some ruggedness. Try to meet with an instrument mechanic(if it is a college project your lab workshop probably has resourceful techs) or a hydrologist.

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#### jacob

Thanks for your ideas. If anyone else is reading, here are my criteria: 1) 4-20ma looks like the best way to go. 2) waterproofing is essential, at least of the sensor and wiring 3) the wiring will go approx 3 metres to a sealed telemetry unit 4) power limited, air no. 5) reliability: good, accuracy: not so important, plus/minus 5% is ok. 6) I visualise the sensor being submerged at all times, the rest of the unit will be sealed from the elements in a container 7) probably go and change batteries / clean solar cells as needed. Unsure of timeframe. I have spoken at length with various river authorities. They all use expensive, proprietary solutions. My aim is to find simpler off-the-shelf components, if possible.

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#### Bob Atwood

Jacob, There are a few options to measure the level as you've described. However when you talk submersible & reliable, cheap doesn't usually accompany it. What is your definition of cheap?? I've seen a few manufacturers of liquid level probes, they run in the $400-$600.00 price range. However accuracy is typically much better ~.1 to .25%. I've personally used the Viatran level probe, they run around \$550.00, with a .1% accuracy. Contact Jerry Webb for information at 716-773-1700 at Viatran if interested Good Luck

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#### David Corking

Jacob wrote: > I have spoken at length with various river authorities. They all use expensive, proprietary > solutions. My aim is to find simpler off-the-shelf components, if possible. At the six hundred dollar range you might get an industrial instrument (transmitter+sensor) more or less assembled to order. Is anyone on the list making "off-the-shelf" pressure transducers - lets say for automobiles - that might be worth a shot for Jacob? If you go industrial here is something that might work. Put a dp level sensor inside the same sealed housing as the telemetry stuff. Run a stainless steel liquid-filled impulse line from the sensor to below the river surface. A liquid-filled impulse line has a diaphragm on the end that transmits the pressure from the water to the special liquid inside the tubing. I would be surprised if the diaphragm got dirty enough to disrupt your readings. You can probably protect the diaphragm from mechanical damage with drainpipe. You need to install the fill liquid in the field - so you need an experienced instrument mechanic to install and calibrate this type of device. David, Delaware in a personal capacity

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