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Author Topic: Fuel Pressure Sensor for Vehicle Application  (Read 1839 times)
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I'm looking for some validation on my choice of products for my intended purpose. I'm a software engineer (UI level) with an old car as a mechanical hobby. Sometimes these two things collide in the middle would of electronics that I know so little about.

Quick explanation of my project: To use my arduino to moitor and log vehicle parameters for the purposes of letting the operator know when those parameters are out of bounds.

My current questions revolve around monitoring the fuel pressure, and the correct pressure sensor to use. I'm trying to come up to speed on the world of sensors and how one describes the sensors, but I could use some help in knowing if my chosen sensor will fit the bill. I try and avoid as many "$90 whoopies!" as I can.

I think I've narrowed it down to the following set of sensor:
http://www.digikey.com/scripts/dksearch/dksus.dll?FV=fff4001e%2Cfff800b3%2C2400035%2C3680003%2C45c009d&vendor=0&mnonly=0&newproducts=0&ptm=0&fid=0&quantity=0&PV252=26

What remains, I am not sure about. For example, for the Arduino and my purpose, which is the ideal output range, 0.5v-4.5v or 1v-5v? How about input voltage? 8v-30v sounds super flexible, but what is the trade off? Any chance that the Hall effect might make a measurable impact on the readings?

The following are all the project parameters that I'm aware of for this particular sensor:
  • Pressure of fuel line 3 bars (43.5psi). High pressure unlikely, mostly detecting low pressure.
  • Under hood sensor location. Need to withstand heat and remain uneffected. However, a cooler location can be chosen so it shouldn't need to withstand anything close to 100C
  • Optional voltage for powering: Varying 12.6v-14v car power Or 5v Arduino output.
  • Accurate to within 5 PSI

And for the sake of argument, let's assume for a second that I know how to blow things up, and not blow things up. Unless someone thinks the sensor will be susceptible to fuel or failure based on the characteristics of the sensor's data sheet, let's start with choosing the sensor and assume I'll be safe smiley

Thanks guys! Let me know if you think I'm missing any parameters that should be taken into consideration when trying to make this measurement.
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I wish I knew if the 21 views and no replies means that I'm spot on, or so far out in left field that I'm not worth helping...

Since I can't decide which one it probably is, I'm probably out in left field, aren't I?  smiley-sad
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I am bamboozled by the three bar fuel pressure.  What sort of car is this ?
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Hey! A Reply! I'll take it smiley

The car is a 1989 BMW 325i, and uses a standard Bosch FPR. and I'm positive that's the correct pressure.

Out of curiosity, do you think it's oddly high, oddly low, or odd that it's measured in Bars? smiley
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Thanks guys! Let me know if you think I'm missing any parameters that should be taken into consideration when trying to make this measurement.

Probably the most important property for the pressure sensor you select for your application is it's compatibility with the media it's measuring, gasoline in your case.

 Most inexpensive pressure sensors are designed for measuring just clean air or other inert gases. Some also allow contact with clear water. Pressure sensors designed for hazardous materials always use a sealed metal diaphragm between the media and the actual sensor element, typically using stainless steel, or in the case of when needing to measure a liquid acid media use  hastalloy or other special metal diaphragm material.

 Make no mistake that the required diaphragm isolated barrier is what makes such sensors cost significantly more then the sensors with no such barrier protection for the sensing element. You tend to get what you pay for in this line of sensors.

 So check carefully the datasheet that covers the specific pressure sensor you are considering for it's media compatibility, never assume compatibility not listed, call the vendor if required. The other specs such as voltage/current measurement range are easier to work through once you get the basic safety required specs matched to your application.

Lefty
« Last Edit: January 23, 2013, 09:31:12 pm by retrolefty » Logged

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Well when I think of "old cars",   it is not fuel injection that I have in mind.

I guess 3 bars sounds high ,  if you don't have fuel injection,   and it sounds low,  if you do have fuel injection.

For antique 1969 fuel injection,  it probably sounds about right.   
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Thanks guys! Let me know if you think I'm missing any parameters that should be taken into consideration when trying to make this measurement.

Probably the most important property for the pressure sensor you select for your application is it's compatibility with the media it's measuring, gasoline in your case.

 Make no mistake that the required diaphragm isolated barrier is what makes such sensors cost significantly more then the sensors with no such barrier protection for the sensing element. You tend to get what you pay for in this line of sensors.

Lefty

Thanks, Lefty. The Data sheet states
"Chemical Compatibilities:   Any gas or liquid
compatible with 304L & 316L Stainless Steel.  For
example,  Motor Oil, Diesel, Hydraulic fluid, brake fluid,
water, waste water, Hydrogen, Nitrogen, and Air."


So I think I'm good. And it's nice to know what I'm paying for when buying a $100 pressure sensor!
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Well when I think of "old cars",   it is not fuel injection that I have in mind.

I guess 3 bars sounds high ,  if you don't have fuel injection,   and it sounds low,  if you do have fuel injection.

For antique 1969 fuel injection,  it probably sounds about right.   

Yeah. The definition of old keeps on changing. While the car is an 89, the body dates to 1984, which means the thing was designed 30 years ago. That's a long time in the automotive world so when choosing between calling it a "new car" or an "old car" I tend to go with the latter, even if it is post many of the seminal car advancements of the last 60 years.

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the simplest solution (I think) would be to use an analog oil pressure sensor
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the simplest solution (I think) would be to use an analog oil pressure sensor

I hadn't thought to use an automotive oil pressure sender... So something like this perhaps?
http://amzn.com/B00029JXMA

This is where I'm rather unsure about how "most" pressure units work. Are they linear output, such that getting a handful of readings from it I can map the rest out pretty easily? Because I'm not finding a spec sheet for it, and I wouldn't really expect to find one for a cheap generic unit like that.

Thoughts? It certainly borders on cheap enough to play around with, but I don't like burning $20s either if someone can tell me that's all I'd be doing smiley
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the simplest solution (I think) would be to use an analog oil pressure sensor

I hadn't thought to use an automotive oil pressure sender... So something like this perhaps?
http://amzn.com/B00029JXMA

 It certainly borders on cheap enough to play around with, but I don't like burning $20s either if someone can tell me that's all I'd be doing smiley

Probably too cheap for the job you want to do. Oil pressure senders in cars aren't that accurate, they don't need to be, and are largely there for decoration, which goes some way to explain why most modern cars don't bother with them.

Two questions, though:

1. Are you sure the system doesn't already have a fuel pressure sensor?

I would have thought that, if it was merited, that would be a pretty obvious item in a modern electronic fuel injection system.

2. What would you do with the data once you obtained it?

I had an older injection system and the manual had nearly as much ink in it telling you what you can't do as telling you what you could do. I imagine the situation has only gotten worse in that respect.


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dude he's on an arduino forum talking about modding his "old" 80s car (my arduino design is getting scrapped for some dedicated ICs and a Raspi going into my 73 VW, but I digress).  Lets not talk about what is sensible or reasonable ok?  I also am finishing a nixie tube dash display....


anyways, a real simple pressure guage to use are the MPX5100s, they take 5v (steal it off the arduino, its regulator will drop the cars 12 to what you need, but will get warm) and will spit out reasonable voltage for your ADC.  Just go thru the choices and pick the right pressure range, I have been using them for low pressure stuff and know they make a 3psi max, 15 psi max, and 100 psi max guages, there may be more inbetween.  However I doubt they are fuel proof, but if you isolate the fuel so only vapor makes it to the sensor, you might make it work.  a length of hose, and vertical placement could let you get by for a while.  the sensor is slightly protected on the inside, and they are only about 16 bucks iirc.  Also you can nab a vacuum guage from the same sensor line, and check MAP or any other fun stuff. I plan on using it to compare fuel pressure to manifold vacuum, as thats how the old VWs enriched under load.

however if you do settle on the perfect sensor, let me know!  thats more money than I want to spend at 90 bucks cause I have a bunch of other sensors going in (accel, cylinder head temp, oil temp, oil pressure) and fuel pressure is just a fun but useless value to know.   I have a analog guage for tune ups, you don't need it while driving, but need is niether here nor there.
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any progress?
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However I doubt they are fuel proof, but if you isolate the fuel so only vapor makes it to the sensor, you might make it work.  a length of hose, and vertical placement could let you get by for a while.

That doesn't work. When measuring liquid pressures there must be no vapour pocket anywhere in the sensing lead as liquids are incompressible and will transfer their applied pressure to the sensor element. Vapour is compressible so will not accurately transfer the applied pressure to the sensor. Liquids and gasses cannot be allowed to mix in the sample line to the sensor as it will cause large errors in measurement values.

Pressure sensors designed for 'hostile' liquid service typical have a stainless steel metallic barrier between the sensor pressure element and the 'process' attachment. Then there is an inert liquid packed between the barrier and the sensor element so that there is no trapped vapour space, so the pressure will transfer accurately.

 A installation rule for pressure sensors is:

If for air/gas/vapour only service, mount pressure sensor higher then pressure sample take off point so any condensation will self-drain back to into the process being measured.

If for liquid pressure service, mount pressure sensor lower then pressure sample take off point so any trapped gas partials will travel up and back into the process.

Failure to follow either of these 'rules' can lead to inaccurate and unstable pressure readings.

Lefty
« Last Edit: February 01, 2013, 08:48:16 pm by retrolefty » Logged

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http://www.ebay.com/itm/Audi-VW-Seat-Skoda-Fuel-pressure-thrust-sensor-06D906051A-06H906051A-03C906051D-/230843184814?pt=Motors_Car_Truck_Parts_Accessories&hash=item35bf5376ae&vxp=mtr

I have one like this sitting on my tool box:  http://www.ebay.com/itm/GENUINE-Audi-A4-A6-Quattro-Volkswagen-Jetta-Passat-Fuel-Pressure-Thrust-Sensor-/121056224772?pt=Motors_Car_Truck_Parts_Accessories&fits=Make%3AAudi&hash=item1c2f836604&vxp=mtr

These will both will meet your requirements, are 0-5v, and will handle well over 4 bar,  check your local audi/vw dealer there is one on every TSI/TFSI(direct injection) engine, and the tech are always throwing these things out.  There is an issue with them causing a check engine light but I feel most are replaced for no reason.  Talk to the techs, a quick explanation of what you are doing and maybe a $20 bill will likely net you one.
« Last Edit: February 03, 2013, 11:48:40 am by js35 » Logged

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