Digital Manometer - looking for transducer

[metrologist]

I'd like to build a multichannel manometer for adjusting combustion engine intake vacuum, 2, 4, 6, or 8 cylinders.

I plan to use an Arduino, but not sure if there are any inexpensive pressure/vacuum transducers that would work for this application?

The ones I'm seeing on digikey are a bit more expensive (~ $12 to $26 each) than I'm hoping to find. Is there a less expensive way to make this kind of sensor (other than typical mechanical dial gauge or liquid column)?

[CJay]

You've got individual throttle bodies for each cylinder?

If you're after a digital interface sensor then Honeywell Sensym have a nice range and they're compatible with fuel. They're cheaper than the ones you've seen but they can and do get *very* expensive

Bosch also have a range, including the dirt cheap BMP280 but that might not be suitable, depends what scheme you're planning.

Airflow and balance is possibly more useful than accurate vacuum measurement, I seem to remember vacuum is more useful as a diagnostic than a tuning aid so a hot wire mass airflow sensor might be better.

[metrologist]

yes, individual throttle bodies or carbs - for motorcycles

Here is a commercial solution: http://www.thedigisync.com/digi-sync-top-page.html

I had also seen the differential pressure transducers - they seem good for 2 cylinders but could not figure out how to make them work for 4 cylinders.

[CJay]

OK, so absolute pressure will do and it doesn't even need to be meaningful measurement, just numbers so you can adjust to match.

Self calibration is just compensating/nulling differences in the sensors when they're not connected to anything.

Measurement range is approx -10PSI to atmospheric if I remember the numbers so the BMP280 won't do, my bad.

Seems you can have cheap unsuitable digital interface sensors, cheap suitable but analogue output sensors or pay a lot more for something suitable.

The prices have dropped over all though if that's any comfort...


*edit* -10 psi duh, I meant  10psi below atmospheric.

[metrologist]

Would the ADP5111 work? If it were only 1/10 the price I'd go for it...

I have lots of clear tubing and ATF...

[CJay]

ADP5111 I think so, possibly ADP41510 which is half the price, as always datasheet needs scrutinising as Mouser say it's digital output, a quick scan of the data sheet suggests analogue (it's 6:30AM and I'm drinking tea and eating toast before leaving for work so that's a job for you I'm afraid  )

Alternatively, if you're OK with small and SMD, how about something from the Honeywell range at a third the price?

http://www.mouser.com/ds/2/187/honeywell-sensing-micropressure-board-mount-pressu-1154293.pdf

I2C, SPI, Absolute or Gauge versions and compatible with fluids (silicone gel versions), apparently on back order so Mouser might not be the best source but...

[max_torque]

Remember that intake pressure down stream of a port throttle is crank angle defendant as there is just a small throttled volume compared to the swept volume of the cylinder........

ie if you want to find the average manifold pressure you need to perform some suitable filtering of the realtime data

[metrologist]

The less expensive Honeywell sensors seem to be + pressure only.