Using Pressure Transducers To Check Exhaust Backpressure

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  • greasybob
    Senior Member
    • May 2008
    • 1590

    Using Pressure Transducers To Check Exhaust Backpressure

    I've been trying to use a pressure transducer to measure exhaust back pressure recently and haven't found it to be all that great. The problem is over sensitivity, it sees all the individual pulses where as a gage gives an average reading. I've put the scope in filter mode, but still looking for a way to get an average reading with out all the spikes, any ideas on what settings to use ? I.ve added a shot from a vehicle that showed 5 psi on the gage but as you can see the scope makes it difficult to find the average. Also should the eveness of the spikes at idle be any indication of the cylinder contribution ?
    Attached Files
  • Joe Rappa
    Snap-on DSD
    • Aug 2007
    • 2050

    #2
    Hi Bob,
    Maybe try using the graphing meter instead of the scope. That might provide enough smoothing to make it useable for backpressure readings.

    Joe
    "You don't build a reputation on what you're going to do"
    Henry Ford

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    • kebo1970
      Senior Member
      • Nov 2008
      • 212

      #3
      transducers

      don't use the scope for exhaust pressure; go to graphing multimeter and use 100psi or 500psi transducer . this will clear up all the extra noise on the screen. i use the 500psi transducer for exhaust,fuel pressure and in cylinder testing.
      Last edited by kebo1970; 08-01-2010, 03:57 PM. Reason: wrong transducer

      Comment

      • greasybob
        Senior Member
        • May 2008
        • 1590

        #4
        I still must be doing something wrong, I solved the backpressure issue and took a transducer reading with the graphing meter but still got a lot of spikes. I removed the 02 sensor and attach a 3/8 hose to an adapter I made from an 02 sensor. I took one sample at 10 seconds and one at 1 second. Any more tips on how to do this to get an average reading. It would be nice to be able to adjust the sensitivity.
        Attached Files

        Comment

        • greasybob
          Senior Member
          • May 2008
          • 1590

          #5
          I'll try again tomorrow morning with an orfice in the hose, maybe that'll buffer the amplitude a little and still give an accurate reading.

          Comment

          • Joe Rappa
            Snap-on DSD
            • Aug 2007
            • 2050

            #6
            Originally posted by greasybob
            I'll try again tomorrow morning with an orfice in the hose, maybe that'll buffer the amplitude a little and still give an accurate reading.
            I've used a needle valve for fuel pressure on 24V Cummins engines. They're pretty inexpensive and easy to use.

            Joe
            "You don't build a reputation on what you're going to do"
            Henry Ford

            Comment

            • greasybob
              Senior Member
              • May 2008
              • 1590

              #7
              I tried several different size orfices and lengths of hoses attatched to the transducer but in the end the best way to clear up the signal is to go to a 25 PSI scale.
              Attached Files

              Comment

              • kebo1970
                Senior Member
                • Nov 2008
                • 212

                #8
                backpressure

                the waveform where you induced backpressure is what i get on the vantage pro. i also use the split screen(digital reading with waveform on the same screen). just use a backpressure tester and take off the gauge; put your transducer in place of the gauge.

                Comment

                • greasybob
                  Senior Member
                  • May 2008
                  • 1590

                  #9
                  Heres probably the best sample I got, this is one at a 25 psi scale I meant to post earlier. I reduced a 5/16 hose to 3/16 then back to 5/16 to try and buff out the spikes. I also used the graphing meter instead of the scope.
                  Attached Files

                  Comment

                  • kebo1970
                    Senior Member
                    • Nov 2008
                    • 212

                    #10
                    exhaust

                    í'll take some shots and post them here. i only use a backpressure tester with a transducer in place of the guage. in graphing multimeter i use 1 or 2 second time sweeps with a digital readout and a graphing scale.

                    Comment

                    • ZAFH15A
                      Junior Member
                      • Jul 2010
                      • 4

                      #11
                      rms?

                      i am not sure if I am missing something here, but if all you want is an average why are you not happy with the rms that your volt meter will give you.

                      Comment

                      • greasybob
                        Senior Member
                        • May 2008
                        • 1590

                        #12
                        Beyond the vain pursuit of measuring things for the sake of measuring them, I'd like to be able if neccessary to show the costumer what needs to be done or the results of what I did to solve a problem. The sensitivity of transducers is normally a good thing but it would be nice if you turn them down a bit for some applications. Maybe get Snap On in the future to put a transducer averaging in the scope menu just as my Vantage has DC Volts averaging in it's menu. If it were just for my use a gage would be fine.

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