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  • Pressure Transducer

    Does anyone know of a hydrualic pressure transducer on the cheap? I've found plenty of gas pressure transducers, but I need one that can plug directly into a hydrualic system without any nitrogen buffer, etc and measure the pressure directly.

    Range would only have to go to 1000 psi, max. (Normally in the 100-500 psi range).

  • #2
    You might look at a capacitance manometer. MKS has ones that will go way past where you want to read and I can think why they wouldnt measure liquid as well as gas. Its just pressure deflecting a diaphragm. Maybe mount it upside down to get the air out.

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    • #3
      I think just the regular cheapo pressure gauge that has a round dial will work. It is the bourbon type pressure gauge. just gotta get the air out. You might want to pay a touch more and get one from a reputable company like wika, where they have a datasheet for the gauge that explicitly says it can measure fluids, and says what the insides are coated with in case there is a possibility of corrosion. U can also google for hydraulic pressure gauge.

      Unless you really mean transducer - what do you want to convert the pressure into?

      edit: never mind, I'm stupid
      Last edited by beanbag; 02-01-2010, 05:42 PM.

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      • #4
        Originally posted by beanbag
        I think just the regular cheapo pressure gauge that has a round dial will work. It is the bourbon type pressure gauge. just gotta get the air out. You might want to pay a touch more and get one from a reputable company like wika, where they have a datasheet for the gauge that explicitly says it can measure fluids, and says what the insides are coated with in case there is a possibility of corrosion. U can also google for hydraulic pressure gauge.

        Unless you really mean transducer - what do you want to convert the pressure into?

        I really want a transducer I would like to convert the variable hydraulic pressure from a brake system into a voltage signal. I've been looking at some transducers on ebay.

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        • #5
          Make a pressure divider and then you can use an ordinary oil pressure transducer from a car.


          Rough drawing, add O-rings on the pistons as required. Pressure at the transducer is of course proportional to the areas of the pistons.

          Free software for calculating bolt circles and similar: Click Here

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          • #6
            Originally posted by Fasttrack
            Does anyone know of a hydraulic pressure transducer on the cheap?
            What kind of budget is there, what pressure capacity is required and
            what signal voltage is desired?

            I have engine oil and brake fluid pressure transducers I use for a data
            logging application - their output is 0-5VDC. At $250, they may not fit
            the criteria for being inexpensive. However, there may be suitable
            OEM units that can be adapted for your purpose - if so they will be
            available from an auto wrecker ...

            Another source may be Omega.

            Edit: After looking at prices on the Omega site, they may not be a
            suitable resource.

            .
            Last edited by EddyCurr; 02-01-2010, 06:00 PM.

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            • #7
              Originally posted by Fasttrack
              I would like to convert the variable hydraulic pressure from a brake
              system into a voltage signal.
              Saw this after posting. Looks to me like moderately high pressures in
              a critical application.

              .

              Comment


              • #8
                Evan's suggestion has some merit, except that the piston o-rings will have some "stiction" and will introduce some response lag, as will the added inertial mass of the piston. Care would have to be taken to eliminate any air between the low pressure side and the low pressure transducer, as the compresability of any air would also slow response.

                Still not a bad idea, I may make use of it in a low speed application.
                Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                ~Practitioner of the Electromechanical Arts~

                Comment


                • #9
                  Originally posted by Fasttrack
                  I really want a transducer I would like to convert the variable hydraulic pressure from a brake system into a voltage signal. I've been looking at some transducers on ebay.
                  after my initial post, I was bothered coz it seemed like too easy of a question. Anyway, for approx $100 or less, you can buy various (brake) hydraulic sensors from honeywell, bosch, etc. Digikey sells a bunch, see here for example

                  http://search.digikey.com/scripts/dk...me=734-1044-ND

                  Browse their catalog plus minus a few pages to get an idea.
                  Just pay the damn $68 and be done with it - don't build additional crap. It's research money, right?

                  If you are super cheap, use your "pulls needles off of a dial" contraption on the bourbon gauge and rig a pot or some kind of rotary sensor to it. Ya cheapskate.
                  Last edited by beanbag; 02-01-2010, 06:03 PM.

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                  • #10
                    A return spring on the low pressure side should alleviate any stiction problems or lag.
                    Free software for calculating bolt circles and similar: Click Here

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                    • #11
                      What about this ?

                      http://cgi.ebay.com/CEC-0-1000-PSI-P...mZ300390931531

                      Or is it too expensive ?

                      .
                      .

                      Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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                      • #12
                        P.S. For brake pressure datalogging, I heard that people like to use sensors up to 3000 psi

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                        • #13
                          Originally posted by Evan
                          A return spring on the low pressure side should alleviate any stiction problems or lag.
                          Stiction is a fact of life in any o-ring application, as the o-ring at rest works to displace any lubricating film between the o-ring and the wall of the cylinder, if the o-ring remains at rest long enough. The o-ring in motion rides up to coast along on a very thin film of oil and presents less resistance to motion. This is also true of hydraulic cylinder seals, and many designs have been evolved to minimize the phenomonon. The pressures in hydraulic actuators tend to relegate stiction to an inconsequential element. Pneumatic cylinders are notorious for erratic motion due to stiction.

                          To be sure, there are many piston-type high pressure switches and transducers, but diaphragm type sensors provide better response. Adding a return spring has no effect on stiction other than helping overcome it. The spring will also introduce a pressure measurement offset that must be taken into account.

                          This may all be moot as Beanbag has come up with a reasonable solution.
                          Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                          ~Practitioner of the Electromechanical Arts~

                          Comment


                          • #14
                            Originally posted by John Stevenson
                            What about this ?

                            http://cgi.ebay.com/CEC-0-1000-PSI-P...mZ300390931531

                            Or is it too expensive ?

                            .
                            It says used. Used or used up?
                            Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                            ~Practitioner of the Electromechanical Arts~

                            Comment


                            • #15
                              Fasttrack,
                              A couple of things. First, define cheap. What accuracy do you need, cheap and accurate are mutually exclusive. As for materials compatability, most good xdcrs have stainless wetted materials, no problem with your hydraulics. Very low pressure xdcrs/xmtrs are typically the devices that can't handle liquids. However, if it's not a welded diaphragm (data sheets don't always tell you that) then the manufacturer is using a seal of some sort, typically an O-Ring in the cheap units, may not be compatible. Will the pressure be pulsating or suddenly increasing or decreasing? That will really mess with some units. You'll need to install a snubber or dampener also. As for a little air entrained in the cavity of the sensor, at 1K psi it will introduce some error, but that's something that can also be handled, but most users don't worry about it . Don't forget you can take a current loop unit, i.e. 4-20 mADC, and measure the voltage drop across a resistor. From your dearth of detail, almost any unit in your pressure range would work for you, for a moment or two.

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