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  #1  
Old 07-30-2010, 10:02 PM
greasybob greasybob is offline
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Default 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 ?
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File Type: jpg 95 R1500 5.2 plugged exhaust.jpg (91.8 KB, 267 views)
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Old 07-31-2010, 06:33 AM
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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
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Old 07-31-2010, 03:13 PM
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Default 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 at 03:57 PM. Reason: wrong transducer
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Old 08-02-2010, 07:41 PM
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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.
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Old 08-02-2010, 07:52 PM
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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.
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Old 08-02-2010, 08:08 PM
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Quote:
Originally Posted by greasybob View Post
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.

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Old 08-04-2010, 05:09 AM
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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.
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File Type: jpg BACKPRESSURE THROUGH 0NE EIGHTH INCH ORFICE.jpg (64.7 KB, 231 views)
File Type: jpg SAME ONE EIGHTH ORFICE 10 PSI SCALE.jpg (69.5 KB, 231 views)
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Old 08-04-2010, 06:27 PM
kebo1970 kebo1970 is offline
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Default 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.
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Old 08-06-2010, 07:11 PM
greasybob greasybob is offline
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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.
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File Type: jpg BACK PRESSURE AT 25 PSI.jpg (66.3 KB, 211 views)
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Old 08-06-2010, 08:05 PM
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Default exhaust

'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.
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