AEM temp sensor scaling

Discuss which Sensors work best with these ECUs and share how you are using inputs and outputs
Simon P.
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Joined: Sat Nov 12, 2011 6:24 pm
ECU Model: S100 Pro
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Location: Montreal, Canada

AEM temp sensor scaling

Post by Simon P. »

Alright, started this in the "sensor scaling" thread but moving it here as a new topic to hopefully get it seen a bit more...
Long story short: I'm trying to use one of AEM's fluid temperature sensors to log/monitor oil temps on my S54B32 swapped 318ti (hatch). The temperature sender part # is 30-2012. I have attached AEM's data sheet.
Scaling on the AEM data sheet is most likely incorrect for the DTA as, from research, AEM EMS's use a 100k internal pull-up and DTA uses (as per Jon in the scaling thread) a 1k pull-up.
Using Jon's scaling spreadsheet and AEM's resistance-temperature scale gives me what seems to be a DTA usable scale but when looking at how the sensor is connected, AEM uses a 2.2k pull-up on the 5v side of the sensor and that's what's screwing me up... I've connected the sensor exactly as per the wiring diagram in the attachement but I'm actually wondering if that 2.2k has anything to do with the DTA's internal 1k pull-up and the scaling values... ie do I need to modify the spread sheet's pull-up value of 1k or is the 2.2k pull-up on the 5v side of the sensor completly different and of no consequence? :?
Hopefully someone can chime in here with a light...
BTW, the sensor DOES work and put out values which "seem" to be in line with my analogue oil temp gauge but I've only tried starting the car and letting it warm up for a short period of time so no idea if the values are correct or would stay correct for the full sweep of the scale...
Attachments
Installation Instructions 30-2012.pdf
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stevieturbo
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Re: AEM temp sensor scaling

Post by stevieturbo »

If you have another gauge to compare with, I'd just go with that. If the two read different you'll always wonder which is correct.

I guess you could maybe try heating the sensor tip with a heat gun and using one of those Infra Red temperature pyrometer thingies and measure temperature and enter values in DTA as you go.
Jon K
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ECU Model: S80 Pro
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Re: AEM temp sensor scaling

Post by Jon K »

I'll have to check out that sensor later (perhaps tonight) but honestly I would use the OBD1 coolant temp sensor for oil temp Simon. I am using a '95 coolant temp sensor which has a preset in the DTA software. It works PERFECTLY. Using it for coolant and oil temperature and they're $11.
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Jon K
Posts: 602
Joined: Fri Dec 04, 2009 1:45 am
ECU Model: S80 Pro
Distributor: DTA UK
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Location: Pennsylvania, USA
Contact:

Re: AEM temp sensor scaling

Post by Jon K »

Here you go Simon - see attached:
Attachments
AEMtoDTA.xlsx
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Simon P.
Posts: 96
Joined: Sat Nov 12, 2011 6:24 pm
ECU Model: S100 Pro
Firmware Version: 61
Location: Montreal, Canada

Re: AEM temp sensor scaling

Post by Simon P. »

Thanks Jon! Just to be clear, I'm also using a BMW OE temp sensor for the water temp for convenience but I needed a NPT threaded sensor for the oil temp as the available port is tapped NPT...
Looking at the excel sheet you've attached, I'm noticing that the DTA values are the exact same ones I used to scale my oil temp input. I obviously got them by using your own spreadsheet available in the scaling thread. ;) So that seams to indicate that the 2.2k pull up on the 5V shown in the AEM wiring diagram has no influence on the scale, right? Because I DID wire that 2.2k in my install... I actually installed it as per the attached sketch (found on some AEM forum, look how the oil temp is wired...) Although the previously attached AEM sensor document seems to show the 2.2K as being internal to the EMS, it's not, as shown in the sketch. I just wired a 2.2k 1/4 watt resistor between the 5V and the signal, same as the sketch... Did I do that wrong? :oops: Should I have simply ommited the resistor??
Thanks.
Attachments
AuXSensorWiringV2.gif
Jon K
Posts: 602
Joined: Fri Dec 04, 2009 1:45 am
ECU Model: S80 Pro
Distributor: DTA UK
Firmware Version: 73
Location: Pennsylvania, USA
Contact:

Re: AEM temp sensor scaling

Post by Jon K »

Simon no no no, remove any resistors. The pull up is internal! You should have no resistors what so ever in your wiring. Just give the sensor power, ground, and wire the signal.

The 1K ohm resistor exists inside the DTA. So you use the table I showed under the DTA Calc column, and you're set.

The only time you need a pullup external is if you want to test the output of the sensor without having it hooked into the ECU. So you could provide 5v and ground and then use the pullup resistor to read the sensor on a volt meter separate of the DTA.
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Simon P.
Posts: 96
Joined: Sat Nov 12, 2011 6:24 pm
ECU Model: S100 Pro
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Location: Montreal, Canada

Re: AEM temp sensor scaling

Post by Simon P. »

OHHH! :roll:
Alright then, give me t'ill the weekend and I'll pull the external 2.2k from the wiring and feed the 5V directly as per the sketch but without the pull up. Then I'll see what kind of reading I'm getting and it should match up to the scale at ambient. If it does, then I'll at least know I'm on thr right track.
Thanks again Jon!
I'll let you know how it goes... :D
Jon K
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Re: AEM temp sensor scaling

Post by Jon K »

Thanks good luck - should totally work
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Simon P.
Posts: 96
Joined: Sat Nov 12, 2011 6:24 pm
ECU Model: S100 Pro
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Location: Montreal, Canada

Re: AEM temp sensor scaling

Post by Simon P. »

Alright Jon, so I tried removing the external pull-up and connecting the 5V direct and that screwed everything up. :o The sensor voltage went full high (4.997V) and would not budge no matter what. (I had removed the sensor and was using a heat gun to heat it up).
The sensor works as expected, it's resistance across both terminals can easily be measured and varies as per the data table. So that rules out sensor issues.
What I don't get is that in the sensor scaling thread you mention that the DTA has a 1K pull up on all sensor inputs. But the AEM 2.2K pull up is not on the sensor input, it's between the 5V source and the input...
Doing a bit of research on NTC sensors like my AEM which, by the way, may be a rebadged Delphi (seems most automotive temp sensors are NTC type), I learned that the circuit that makes them work is called a voltage divider. Basically, you feed 5V through a known resistor and through the NTC sensor and tap the voltage signal right in between them to feed whatever logic circuit your using to interpret the voltage signal. See diag attached.
vdiv7.gif
vdiv7.gif (1.49 KiB) Viewed 9210 times
You can see that if you remove the resistor between the 5V source and the sensor (Rtop), you would have a constant 5V on the input which is exactly what seems to have happened to me when I removed the 2.2k...
So what now? I'd appreciate your input on this. Kinda funny how a freakin 40$ sensor can be such a PIA... :lol:
stevieturbo
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Re: AEM temp sensor scaling

Post by stevieturbo »

Hold on a minute.

What way are you trying to wire this thing up ?

Info on first link says there are two pins. Ground and signal.

So why are you connecting 5v to anything ?

The only place there should be 5v on a 2 pin temperature sensor, comes internally from the ecu on the signal line because of the pullup resistor.

You certainly do not apply 5v from anywhere else. In fact YOU dont apply 5v from anywhere.

Ground and signal wires only.
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