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Location:
sunny coast, qld
Registered:
October 2002
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3 bar map sensor voltage
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Sat, 23 July 2005 05:32
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Would I be correct in assuming that the voltage points on a 3 bar map sensor are
0V = -1 bar
1.66V = 0
3.33 = 1bar
5v = 2bar
Thanks
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Location:
Brisbane
Registered:
February 2003
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Re: 3 bar map sensor voltage
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Sat, 23 July 2005 08:20
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yup - map sensor should have linear voltage response across the range of the sensor.
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Location:
Perth
Registered:
May 2003
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Re: 3 bar map sensor voltage
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Sat, 23 July 2005 11:38
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If you are assuming perfect 1 bar atmospheric pressure with respect to absolute pressure then you could say the sensor would read -1 bar with respect to atmospheric pressure. It is better to be relative to absolute pressure (hence the name Manifold Absolute Pressure sensor) as atmospheric pressure varies depending on altitude and environmental conditions.
Something to note, absolute zero wont give you a reading of exactly zero and 3 bar (w.r.t. absolute) wont be 5V. This is because the extreme regions 0V or 5V are left out of the normal operating voltage range so that if the analogue to digital converter (in the ECU) returns a value indicating the sensor voltage is at or close to 0V or 5V then the ECU assumes the sensor must be in fault (e.g. short or open circuit) and then handles the fault appropriately.
The only true way to determine the voltage v.s. pressure is of a particular MAP sensor is to get hold of the datasheet for the sensor from the manufacturer.
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Location:
Brisbane
Registered:
February 2003
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Re: 3 bar map sensor voltage
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Sat, 23 July 2005 13:10
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i should have said - yup - but 0V = absolute vacuum & 5V=3bar and from memory it should be a linear response (anything i've read about map sensors suggests this).
fwiw, a 2 bar MAP sensor should be able to handle up to 21psi boost.
fwiw 2, you could have the map sensor with 6 foot of piping between in and the sensor and not have any noticable delay in readings (see
[url=http://www.msefi.com/msinfo/manual/mwire.htm#map[here[/url] for more info). air doesn't have the mass (right term?) of liquid and wil move very quickly inreponse ot vacuum or boost.
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Location:
Perth
Registered:
May 2003
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Re: 3 bar map sensor voltage
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Sun, 24 July 2005 09:17
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If you are getting the 21 PSI boost from the Megasquirt site then the sensor they specify is actually 2.5 bar absolute so (2.5 * (14.7)) - 14.7 = 22 PSI of boost, but that would be pushing the limits of the sensor! If you are talking true 2 bar then the boost is only 14.7 PSI.
I agree that the sensor can probably read slightly higher than its operating range but it wouldn't be desirable to operate it there. Technically you could probably also run a lot higher pressure before permanently damaging the sensor diaphragm but this would be useless as you wouldn't be getting a useful voltage reading anyway.
Yes, the longer pipe wouldn't affect the response much as you said. The total response of the engine is relatively slow in comparison to the speed that the calculations are performed in software.
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