H20 pressure transducer

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Technician
TwoWaves
TwoWaves
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Joined: Thu Apr 24, 2014 8:32 pm

H20 pressure transducer

Post by Technician »

I was reading something the other day and the diagnostic tech was using some form of H20 pressure transducer for measuring intake vacuum pulses and exhaust back pressure pulses. So this got me thinking, if when I have engines as none starters should I use the WPS500X in cylinder and either one or two H20 pressure transducers in the other areas, such as intake manifold and exhaust tail pipe?

I was also wondering whether a MAP sensor would be okay for the same type of tests?

Any views on this.

Steve Smith
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Re: H20 pressure transducer

Post by Steve Smith »

Hello and thank you for the post

Sorry I am not familiar with the H20 pressure transducer other than a quick internet search

If you have a WPS I would initially deploy this tool in such a way that the results produced generate an initial diagnosis

The initial diagnosis (where possible) is non-intrusive and so I would not remove a spark or glow plug to get “in-cylinder”

I would stick with your suggestion of WPS via the exhaust tailpipe (cranking pulsation) and utilize the MAP sensor if installed

We often forget the MAP sensor is a ready-made pressure transducer within the intake. All we need to do is AC couple the signal wire from the MAP sensor to capture intake pulses during cranking or engine running

Another option is MAF meter pulsations (analogue or digital) as we often capture uniform ripples within the intake airflow if the engine is preforming correctly. i.e. even intake pulls
Ensure EGR not active as this disrupts airflow pulsations

Once we have obtained “direction” during the initial tests we can then evaluate the level of intrusion required which may be in-cylinder application of the WPS

I hope this helps, take care…Steve

Technician
TwoWaves
TwoWaves
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Joined: Thu Apr 24, 2014 8:32 pm

Re: H20 pressure transducer

Post by Technician »

Thanks for the reply Steve.

With reference firstly to the MAP sensor idea as a use of measuring pressures, some time back ( a few years) I worked on the low fuel pressure side of the diesel fuel system and found that a fuel system pressure sensor was fitted alongside the nearside front chassis rail. Research I concluded found that the fuel pressure sensor was indeed a MAP sensor used by Land Rover. Now that got me thinking that as it is a MAP sensor that measures vacuum (negative pressure), but seems to be able to measure a positive pressure also, then what would stop me using a MAP sensor to assess inlet manifold depression and crankcase depression?

Referring now to the First Look Sensor that Pico sell, manufactured by SenX Technology, I was wondering how sensitive a measurement that delta transducer provides from an accuracy point of view if say I used that for exhaust back pressure, and inlet manifold or crankcase pressure measurements?

I won't mention the name of the company but I've found that one absolute pressure sensor that measures up to 100 PSI when used as a in-cylinder transducer will not record valve events because the sensor is not able to measure below atmospheric pressure?

I'm just researching ideas at the moment, I want to be in a position whereby I can achieve four signatures all at the same time instead of stopping and starting moving components around etc. Timing of events within the same test cycle I think is important when multiple measurements are taken from various locations at the same time. An intermittent glitch could occur but then be missed if not measured at the exact same time.

Any views on this?

Steve Smith
Pico Staff Member
Pico Staff Member
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Joined: Sun Aug 25, 2013 7:22 am

Re: H20 pressure transducer

Post by Steve Smith »

Hello David and thank you for the feedback

I am going to stick with your initial post regarding the measuring/capture of intake and exhaust pulses

From an initial (non-intrusive) diagnostic point of view, the formation, uniformity, timing & correlation of such pulses is predominately our main concern (Not the measuring of pressure values)

Therefore, any sensor capable of responding accurately to intake and exhaust pulses is going to be of benefit. (This could be MAP, MAF, WPS, First Look ((FL)) or even a home-made device)

Forgive me here as I don’t fully understand “as it is a MAP sensor that measures vacuum (negative pressure), but seems to be able to measure a positive pressure also, then what would stop me using a MAP sensor to assess inlet manifold depression and crankcase depression?”

Once again, we are looking at pulses and a pressure sensor that responds to both positive and negative pressure can only be a benefit

If you wish to use a MAP sensor capable of measuring both positive and negative pressure (in order to display pressure valves) the following forum post will help viewtopic.php?p=99396#p99396 where I have looked at graphing the output from such a MAP sensor

The sensitivity of MAP and MAF sensors is more than sufficient to evaluate engine running concerns.
Equally, the sensitivity of both the WPS and FL sensors are more than capable of providing accurate pulsation timing and correlation values. (They are designed for such use)
Remember the FL will give you pulsations, the WPS will give you pulsations and pressure values across numerous applications

The specifications of the WPS can be found here https://www.picoauto.com/products/press ... r#finfDocs

Further information on the FL sensor can be found here http://senxtech.com/senxtech/how-it-works/

I could not agree more with David re “Timing of events within the same test cycle I think is important when multiple measurements are taken from various locations at the same time. An intermittent glitch could occur but then be missed if not measured at the exact same time.”

I hope the above goes someway into assisting you achieve this goal with the variety of options at your disposal

Take care……Steve

Technician
TwoWaves
TwoWaves
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Joined: Thu Apr 24, 2014 8:32 pm

Re: H20 pressure transducer

Post by Technician »

Thanks Steve for your valuable experinces and input, they are very much appreciated. yes reading back I can see some of my post was badly worded (poor state of health at time of writing) but if I sat back and waited until I was okay, I'd probably call it a day. I did a little more research on the H2O pressure sensor operation and as you point out its not the differences in the signature that is important, but as you say the formation, uniformity, timing & correlation of such pulses is predominately the main concern. I'm going to make something up to ensure that I can test both the intake and exhaust system at the same time as a minimum, again as I think you pointed out previously, and using a syc I should be in a position to establish what occurs first time round in a 720 degree engine cycle.

Thank you for your input.

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