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  #1  
Old 01-17-2012, 01:19 PM
leemack leemack is offline
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Default 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
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  #2  
Old 01-17-2012, 01:28 PM
DougMontgomery DougMontgomery is offline
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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
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Old 01-17-2012, 02:42 PM
leemack leemack is offline
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Default

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.
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Old 01-17-2012, 03:46 PM
DougMontgomery DougMontgomery is offline
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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).
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Old 01-17-2012, 04:09 PM
leemack leemack is offline
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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
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  #6  
Old 01-17-2012, 08:27 PM
Rich Shepherd Rich Shepherd is offline
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Default

Quote:
Originally Posted by leemack View Post
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:
http://www1.snapon.com/diagnostics/us/VERUS
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.
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Old 01-18-2012, 07:51 AM
leemack leemack is offline
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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.
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Old 01-18-2012, 02:14 PM
DougMontgomery DougMontgomery is offline
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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.
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Old 01-18-2012, 03:16 PM
leemack leemack is offline
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Default

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
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  #10  
Old 01-18-2012, 09:34 PM
Rich Shepherd Rich Shepherd is offline
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Some more information:
The usable range of the 100PSI transducer on the vacuum side is just a bit more than 20ĒHg which is the reason for the 20Ē 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 itís 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.
Itís 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
Itís relatively inexpensive here in the US. I donít know what it may be in your location.
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