pressure transducer, which one

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  • leemack
    Member
    • Jul 2010
    • 49

    pressure transducer, which one

    I'm looking to purchase a pressure transducer but can't decide which one/type. I think the 0-500 psi standard type will be fine which costs £171 or I can buy a fluke pv350 for £250 which is identical to the more expensive snapon version.

    I'd rather save the extra £80 but if its more adviseable to buy the fluke then I will. Also I dont like the idea of the selector switch on the fluke/snapon expensive transducers.

    I had a search through this forum but no one has actually said which one is the best. I will be using it with a modis.

    Thanks
    Lee
  • DougMontgomery
    Senior Member
    • Jul 2007
    • 194

    #2
    Lee,

    I know there is or was conversation of pressure transducers here. If you going to use a Snap-On Scan Tool that has the pressure capabilities built in (IE vertical PSI table and also powers up the packard styl connector transducer), then your kinda limited. Snap-On's 0-500 PSI has a transition time of about 10 mS and most notibly has an inherant flaw, like some other transducers, that it's zero shifts when transitioning from a static pressure to a dynamic pressure. If you don't mind your those points..then your o.k. with the Snap On 0-500 PSI.

    The Fluke PV350 is not affected by the zero offset, however its small issue is it's noisy. Most either ground the case of the transducer element with a alligator clip to ground or filter it out with their scope..or a combination of the two.

    The other two available are the Pico WPS500, which is a great unit. Again, not affected by the zero offset and has many features unique..that may appeal to you.

    Lastly, I developed a VAC-300 PSI transducer and interface modules (Dual & Single Channel) that is the transducer itself has EMI/RFI shielding, it is not affected by the zero offset issue, the interface is EMI shielded and the cabling is dual shielded (foil & braid). Moreover, I have incorperated passive filtering in the interface. This allows you to filter the signal BEFORE the frontend of your scope. There are many reasons that is benificial...which would be another discussion.

    Hope this helps

    Comment

    • leemack
      Member
      • Jul 2010
      • 49

      #3
      So would you not recommend the standard 0-500psi transducer for a beginner.

      Could you explain more about the zero shift error and what problems the 10ms transmission response time can cause.

      Can't afford the Pico WPS500 as its around £500 in the uk. Could buy the Fluke version which is around £200 cheaper than the Snap-on equivalent but would this really benefit me much more.

      I want to beable to do running compression tests, check valve timing, check exhaust back pressure and other things such as turbo boost issues.

      Thanks
      lee

      p.s

      my snap-on rep in the UK has only ever sold one in his time of being a snap-on dealer so he can't offer any advice either.

      Comment

      • DougMontgomery
        Senior Member
        • Jul 2007
        • 194

        #4
        Lee,

        I did not say I would not recommend the Snap On 0-500 PSI transducer. Please re-read my post. If you want to have the convenience of the PSI on the left vertical scale, power-up the transducer from your Snap-On Tool (Modis, Vantage, Veris, Verdict) and don't mind the PSI scale being in-accurate when performing in-cylinder running compression testing..then it's probably for you.

        The 10 mS transition time may not be a big deal to you, since your just starting out. Plus, most valve/airflow concerns diagnosis's will not be hampered do to the slower transition time of the unit.

        The zero offset is just as I explained. When taking static readings, after the tool zero's to the transducer. If you are doing a in-cylinder running compression test, the conditions in the cylinder cause the transducer to skew from center (being zero'd..ie accurate).

        Comment

        • leemack
          Member
          • Jul 2010
          • 49

          #5
          I was thinking maybe use the 0-500 transducer om the scope but use a voltage scale sometimes as well for greater accuracy if ever needed.

          I see a post that converts mV into psi readings.

          This does sound like it will suit my need for now.

          Thanks
          Lee

          Comment

          • Rich Shepherd
            Snap-on D&I
            • Nov 2006
            • 553

            #6
            Originally posted by leemack
            I was thinking maybe use the 0-500 transducer om the scope but use a voltage scale sometimes as well for greater accuracy if ever needed.

            I see a post that converts mV into psi readings.

            This does sound like it will suit my need for now.

            Thanks
            Lee
            To connect the Snap-on 0-500 pressure transducer to your Modis, you will need the Split Lead Adapter part number EEMS301A05 found here:

            The same adapter lead is used for Modis, V Pro, and Verus.

            It's not practical to use the transducer without the adapter lead.

            The transducer requires 5V to power it. The adapter lead lead supplies 5V and ground to the transducer from the 9 pin connector on the scope. It also connects the signal output of the transducer to the scope channel you want to use it on.

            Comment

            • leemack
              Member
              • Jul 2010
              • 49

              #7
              The problem is the max vacuum reading scale on a MODIS is 20 inhg which isn't low enough for a good running engine so testing engine vacuum performance would be an issue but if you could use it as a voltage scale you'd beable to read/adjust to suit.

              You can convert the voltage to the correct vacuum/pressure reading from a chart i copied from this forum.

              Comment

              • DougMontgomery
                Senior Member
                • Jul 2007
                • 194

                #8
                Lee,

                Unfortunately, the Snap On Tools that support native transducers (Modis, Veris, Verdict..etc) only supply the 5VDC and GND when you SELECT pressure from your menu. So, if you selected normal scope mode, even using the transducer with the cable would be futile..since the tool would not power them up. Hence why I developed a interface that not only powers up the transducer (an any packard 3 pin style connector type) but has shielding and filtering internal.

                You are asking good questions and such a purchase, especially when using it to ease diagnosis of vehicles, can be expensive. If I remember correctly from years ago, the Snap On 0-500 PSI transducer will be upwards of $250-290 each and the cable mentioned above is $70+. Then I believe they make an addition "Y" cable to allow two transducers to be utilized.

                Comment

                • leemack
                  Member
                  • Jul 2010
                  • 49

                  #9
                  I can buy the 0-500 psi transducer and the cable for £171 which i think is around $261 which i don't think is to bad or the Fluke PV350 for £200/$307.

                  In one way it would be nice just to have a reading in PSI/inHg on the screen straight off rather than converting a voltage reading to determine the pressure/vac amount.

                  I also like the idea of being able to use the rpm pickup along side the pressure transducer to sync the reading to determine which cylinder is at fault which i think is possible with the split lead.

                  Won't buy the Y adaptor as i don't see the need for 2 transducers yet. Obviously the WPS500 would be the perfect answer but i think its out of my price range really especially as i'm just learning the ropes of scoping etc.

                  I wanted to have both types of transducers (snap-on equivalent to the Fluke) on trial but here in the UK Snap-on aren't like that and even the dealer said no chance of that happening.

                  I could afford the Fluke version but as you said its noisey which i think will confuse me and possibly annoy me at the same time, this then will cause me not to want to use it.

                  So basically i'm in a situation that i can't really find an answer to, i don't like the idea of not being able to read vacuum lower that 20inHg but would like an image easy to understand.

                  I actually do have a dedicated pressure/vacuum transducer with my old Ford WDS machine (100psi) but never actually used it with the inbuilt oscilloscpe.

                  Anyway thanks for your help, i need you to help make up my mind as you seem to really understand this subject.

                  If i buy from the USA i end up with duty charges which ends eup being a fair amount as i found out when i bought the upgraded test leasd for my MODIS from AES.

                  thanks
                  lee

                  Comment

                  • Rich Shepherd
                    Snap-on D&I
                    • Nov 2006
                    • 553

                    #10
                    Some more information:
                    The usable range of the 100PSI transducer on the vacuum side is just a bit more than 20”Hg which is the reason for the 20” scale.
                    Also note that the .5V is the zero point of all 3 of the Snap-on transducers. Vacuum is below .5V and pressure above .5V.
                    For this reason and that the transducer requires 5V to power it is why I said it’s not practical to use the transducer without the split lead adapter I mentioned.
                    If you built an adapter to power it and then input the signal to one of the scope channels set to a voltage scale instead of pressure, you not only have to convert the output from Volts to PSI (or vac as the case may be), you also have to account for the .5V offset.
                    It’s more convenient to have pressure readings displayed directly in PSI

                    The Split lead adapter allows 2 pressure transducers and the RPM/Cyl 1 trigger lead to be connected to the scope at the same time so a Y adapter is not needed to connect 2, only the Split Lead Adapter.
                    The price in the US can be seen here:
                    http://buy1.snapon.com/catalog/item.asp?store=snapon-store&item_ID=67127&group_ID=19978
                    It’s relatively inexpensive here in the US. I don’t know what it may be in your location.

                    Comment

                    • leemack
                      Member
                      • Jul 2010
                      • 49

                      #11
                      Thanks for the advice,

                      In the UK it seems things are more expensive than they need to be, the split lead is $41 or £31 GBP + VAT (another 20%) which still isn't the end of the world.

                      Why can't things be easy, zero pressure = zero volts. Anyway i'll decide in the next couple of days.

                      thanks
                      lee

                      Comment

                      • DougMontgomery
                        Senior Member
                        • Jul 2007
                        • 194

                        #12
                        Originally posted by leemack
                        Why can't things be easy, zero pressure = zero volts. Anyway i'll decide in the next couple of days.

                        thanks
                        lee
                        Lee do to voltage divider network..it cannot be 0 volts. That's also why a TPS circuit code is set at 0.2 & 4.8 VDC. The ECM has a fixed resistor inside to put in series with the TPS.

                        Comment

                        • leemack
                          Member
                          • Jul 2010
                          • 49

                          #13
                          This is my last question,

                          In your opinion is it worth while me buying one of these, will it be useful and not a waste of money.

                          I will order one on your say so.

                          thanks
                          lee

                          Comment

                          • DougMontgomery
                            Senior Member
                            • Jul 2007
                            • 194

                            #14
                            Lee,

                            As long as you ask people as many questions about in-cylinder pressure testing as you did about the purchase..you'll be fine.

                            If I could suggest, get the John Thornton AVI video (3 disc set !)...it will help you a lot. Also, Bernie Thompson has some great info on his website (automotive test solutions)

                            Good Luck !

                            Comment

                            • leemack
                              Member
                              • Jul 2010
                              • 49

                              #15
                              Don't forget i'm in the UK but where can I get theze discs from.

                              Comment

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