MakeEverything
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| posted on 25/9/10 at 09:41 PM |
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Megasquirt Temperature Reversed?
Hi all,
Ive tried to calibrate the Inlet air sensor, and have confirmed the readings that i have taken with someone elses. They are all very similar,
however;
When i connect the sensor to the ECU, it reads 10 degrees C, and when breathed on, falls to below 0.
Anyone experienced this before? Ive reversed polarity on the off chance, and still no change as expected.
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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matt_gsxr
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| posted on 25/9/10 at 10:09 PM |
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Temp sensors are just resistors, so nothing too clever there.
Have you got the resistance versus temperature datapoints?
I know that the Megasquirt default sensors are negative temperature coefficient.
"
MegaSquirt uses coolant and air temperature sensors to determine the warm-up characteristics of the engine and the density of the intake air. They are
essential to proper functioning of a MegaSquirt® controller. Both sensors are Negative Temperature Coefficient (NTC) thermistors. This means that they
are resistors whose resistance decreases as their temperature goes up."
If your sensor is PTC then that would cause the effect that you see. I don't know whether megasquirt can handle PTC sensors.
According to this site, EasyTherm isn't good with PTC sensors.
http://www.vems.hu/wiki/index.php?page=EasyTherm
Matt
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MakeEverything
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| posted on 25/9/10 at 10:28 PM |
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quote:
Originally posted by matt_gsxr
Temp sensors are just resistors, so nothing too clever there.
Have you got the resistance versus temperature datapoints?
I know that the Megasquirt default sensors are negative temperature coefficient.
"
MegaSquirt uses coolant and air temperature sensors to determine the warm-up characteristics of the engine and the density of the intake air. They are
essential to proper functioning of a MegaSquirt® controller. Both sensors are Negative Temperature Coefficient (NTC) thermistors. This means that they
are resistors whose resistance decreases as their temperature goes up."
If your sensor is PTC then that would cause the effect that you see. I don't know whether megasquirt can handle PTC sensors.
According to this site, EasyTherm isn't good with PTC sensors.
http://www.vems.hu/wiki/index.php?page=EasyTherm
Matt
Thanks Matt,
My sensors are NTC and have readings which prove that. 4kohms at 15 degrees down to 400 ohms at 80 degrees.
I had to reduce the Bias Resistor figure down to 110 to get an accurate start temperature, and upon breathing on it, came up against a reducing
reading.
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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matt_gsxr
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| posted on 25/9/10 at 10:36 PM |
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I thought I had nailed that one, but not this time!
So, I don't know.
The default resistor is 2490 Ohm. I don't know whether going as low as 110 Ohm will have some nasty effect.
As you can tell I am guessing.
Matt
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MikeRJ
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| posted on 25/9/10 at 11:01 PM |
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quote:
Originally posted by matt_gsxr
I thought I had nailed that one, but not this time!
So, I don't know.
The default resistor is 2490 Ohm. I don't know whether going as low as 110 Ohm will have some nasty effect.
It will: self heating. With a bias resistor that low there will be significant current flowing through the sensor, which being a resistor converts
this to heat...
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MakeEverything
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| posted on 25/9/10 at 11:20 PM |
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What does the bias resistor do amd what does this figure mean? Do i need to fit a resistor in line or does it act as an offset?
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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matt_claydon
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| posted on 26/9/10 at 09:26 AM |
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quote:
Originally posted by MakeEverything
What does the bias resistor do amd what does this figure mean? Do i need to fit a resistor in line or does it act as an offset?
Goolge 'voltage divider' to see how it works. In the case of MS one of the resistors is the bias and the other is the sensor.
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MakeEverything
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| posted on 26/9/10 at 09:57 AM |
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Thanks, so i need to install a resistor physically then? I didnt see anything mentioned about this on Megamanual or Extra EFI??
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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matt_gsxr
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| posted on 26/9/10 at 10:10 AM |
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Look at step 54 on this page
link to build manual
This is how it works.
The bias resistor is in the Megasquirt box, and is in series with the temperature sensor. The megasquirt applies voltage at the end of the bias
resistor and earths the return from the sensor. It detects the voltage across the bias resistor.
So you have:
5v
bias resistor
voltage sensing
temperature dependent resistor (sensor)
0v
As the resistance of the temperature sensor varies, the voltage detected by the MS ECU varies.
(the 0v and 5v may be swapped, I haven't looked at the actual circuit, as it is just a voltage divider, and in this context it doesn't
matter)
The default resistor is 2490 Ohm, and although my sensors are not well matched to the 2490 Ohm it still does a good job (absolute temperature
precision isn't even that critical).
Matt
[Edited on 26/9/10 by matt_gsxr]
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MakeEverything
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| posted on 26/9/10 at 10:35 AM |
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Aaah i see. Thanks Matt. Still not sure how to overcome my problem, other than to try and enter the highest temperature first in the calibration
table. If not, it looks like ill need another OEM sensor for my fault finding.
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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ashg
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| posted on 26/9/10 at 02:39 PM |
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just go to the scrappie and get a few gm (e.g vauxhall saab) temp sensors and run the ms recommended setup. much easier than mucking about replacing
the resistors.
Anything With Tits or Wheels Will cost you MONEY!!
Haynes Roadster (Finished)
Exocet (Finished & Sold)
New Project (Started)
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MakeEverything
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| posted on 26/9/10 at 03:58 PM |
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quote:
Originally posted by ashg
just go to the scrappie and get a few gm (e.g vauxhall saab) temp sensors and run the ms recommended setup. much easier than mucking about replacing
the resistors.
Im not replacing the resistors?
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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matt_gsxr
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| posted on 26/9/10 at 07:41 PM |
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I don't really understand what you 110 Ohm bias resistor is doing? Do you have the stock 2490 Ohm one in the ECU? If not go back to the
original.
If using MS1 then use Easytherm to do the calibration.
If MS2 then do it using the sensor calibration options in TunerStudio.
If this doesn't help, the perhaps hit the MS forums, as someone will have seen your problem before.
Matt
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MakeEverything
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| posted on 26/9/10 at 07:56 PM |
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quote:
Originally posted by matt_gsxr
I don't really understand what you 110 Ohm bias resistor is doing? Do you have the stock 2490 Ohm one in the ECU? If not go back to the
original.
If using MS1 then use Easytherm to do the calibration.
If MS2 then do it using the sensor calibration options in TunerStudio.
If this doesn't help, the perhaps hit the MS forums, as someone will have seen your problem before.
Matt
Hi Matt,
The 110 ohm is the Bias Resistor value in the MS2 TunerStudio Thermistor Calibration Tables. As far as im aware, the Hardware resistors are standard
2490.
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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matt_gsxr
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| posted on 26/9/10 at 08:53 PM |
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So I am getting there now. You are running MS2. Excellent good choice.
You have the standard 2490 Ohm bias resistor.
You have a sensor that should work fine.
Where does the 110 Ohm value come from? Unless you have changed from the original bias resistor (which you haven't) then you should be typing
2490 in the bias resistor. Fiddling with this value isn't a good idea.
It might be worth checking the sensor wiring (especially the earth).
Matt
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MakeEverything
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| posted on 26/9/10 at 08:59 PM |
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The 110 ohms is the bias that gets my sender on the gauge and able to see any changes. Anything else takes the sender reading off the scale.
I think it may be this that has just made my ECU smoke a bit!
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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daxtojeiro
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| posted on 8/10/10 at 08:27 PM |
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Hi,
are you sharing the sensor with a gauge? The coolant sensor (like the air sensor) must only have a ground wire and the ECU connection, it cant be
shared with a gauge Im afraid. You must add another sensor for the gauge, if not you will damage your ECU,
Phil
[Edited on 8/10/10 by daxtojeiro]
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MakeEverything
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| posted on 8/10/10 at 09:49 PM |
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quote:
Originally posted by daxtojeiro
Hi,
are you sharing the sensor with a gauge? The coolant sensor (like the air sensor) must only have a ground wire and the ECU connection, it cant be
shared with a gauge Im afraid. You must add another sensor for the gauge, if not you will damage your ECU,
Phil
[Edited on 8/10/10 by daxtojeiro]
Nope, not sharing it at all.
I got my new sensors yesterday, and it all works fine now. Trouble is, i now have a software Bias Resistor value of 24900 to give me the correct
reading, rather than 2490.
Still puzzled, but now both sensors are reading correctly and going in the right direction!
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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