Hooking up temp sensors to the EMS

[JR]

By far the most common type of temp sensor used is the thermister type which is a resistor that changes is value based on the temperature. The calibrations usually supplied with these is resistance (Ohms) vs. temp. To convert this value into a voltage that can then be entered into the EMS calibration, use this equation:

EMS Volts = 5.00 * ( Resistance / ( Resistance + 2,200 ) )

Or you can just use this table:

Ohms - Volts
50 - 0.11v
100 - 0.22v
200 - 0.42v
400 - 0.77v
600 - 1.07v
800 - 1.33v
1,000 - 1.56v
1,200 - 1.76v
1,400 - 1.94v
1,600 - 2.11v
1,800 - 2.25v
2,000 - 2.38v
2,200 - 2.50v
2,400 - 2.61v
2,600 - 2.71v
2,800 - 2.80v
3,000 - 2.88v
3,500 - 3.07v
4,000 - 3.23v
4,500 - 3.36v
5,000 - 3.47v
5,500 - 3.57v
6,000 - 3.66v
6,500 - 3.74v
7,000 - 3.80v
7,500 - 3.87v
8,000 - 3.92v
8,500 - 3.97v
9,000 - 4.02v
9,500 - 4.06v
10,000 - 4.10v
11,000 - 4.17v
12,000 - 4.23v
13,000 - 4.28v
14,000 - 4.32v
15,000 - 4.36v
16,000 - 4.40v
17,000 - 4.43v
18,000 - 4.46v
19,000 - 4.48v
20,000 - 4.50v
30,000 - 4.66v
40,000 - 4.74v
50,000 - 4.79v
60,000 - 4.82v
70,000 - 4.84v
80,000 - 4.87v
90,000 - 4.88v
100,000 - 4.89v

This information does not apply to the EGT Inputs.

[ef9]

Most OEM manufacturers use thermisters for their temperature gauges(i.e. coolant temp).  Where else can we find thermisters on our automobiles?

How is the accuracy of a thermister compared to an RTD?

Stan

[JP]

Thermistors are very very linear (accurate) but in a small temperature range. Outside of there normal temperature range a thermister is very nonlinear. Typically, IAT and CLT sensors are thermistors.

RTDs (Resistive Temperature Detector) have a wider range of use (ie: 1,000 C) and are almost totally linear. They also can withstand very high temperatures like thermocouples. Thermocouples are more rugged but not as accurate, stable, and responsive as an RTD. Typically, RTDs are used for EGT sensors.

[Kenneth Steinbach]

AEM guys,
The cool sensor table default settings for the Supra don't seem to make sense to me. The maximum temperature (0 volts) is 91 degrees which is pretty much normal operating temperature. When the engine is actually running at this temp the EMS only shows about 80 degrees. Jason, what numbers are you using in this table for your Supra?

[JP]

AEM guys,
The cool sensor table default settings for the Supra don't seem to make sense to me. The maximum temperature (0 volts) is 91 degrees which is pretty much normal operating temperature. When the engine is actually running at this temp the EMS only shows about 80 degrees. Jason, what numbers are you using in this table for your Supra?

We have updated the precision of the Coolant and AIT Tables for V0.89.

[falconGSR]

ahh ok i was trying to figure out what the 5v pullup was on the AIT signal line... 2.2kohm. thanks  

[cbender]

I've a Honda S2000, and based on empirical measurement (i.e., by comparing my coolant temperature using an external probe inserted very close to the stock temperature sensor), it's clear that the temperature calibration table in version 1.03 is reading too high, by varying amounts, depending upon the temperature.  Other S2000 owners with EMS's and temperature gauges have experienced similar problems.  My car, for example, which always ran within the recommended operating temperature was suddenly running "hot" by 15 degrees with the EMS, when no other changes were made to the car.  What are you doing to correct this, and where did your voltage calibration tables come from?  I've no doubt that the table currently offered is wrong.

Thanks,
Christopher

[JP]

I've a Honda S2000, and based on empirical measurement (i.e., by comparing my coolant temperature using an external probe inserted very close to the stock temperature sensor), it's clear that the temperature calibration table in version 1.03 is reading too high, by varying amounts, depending upon the temperature.  Other S2000 owners with EMS's and temperature gauges have experienced similar problems.  My car, for example, which always ran within the recommended operating temperature was suddenly running "hot" by 15 degrees with the EMS, when no other changes were made to the car.  What are you doing to correct this, and where did your voltage calibration tables come from?  I've no doubt that the table currently offered is wrong.

Thanks,
Christopher

The Coolant Sensor values come directly from the Honda Service Manuals.

[cbender]

JP, I'm sure you know more about this than I do, but I've got a friend who's the lead mechanic and Brown's Honda near Washington, D.C., and he was unable to FIND a table that converts voltages to temperatures for the S2000 when I asked him about this.  Can someone check the original source for this data?  Are we certain that the temperature calibrations are the same for ALL Honda vehicles?  

Thanks,
Christopher

[westy]

"Are we certain that the temperature calibrations are the same for ALL Honda vehicles?"  At some point I found a Honda AIT sensor calibration chart on the AEM web.  It had a drawing of the sensor.  The drawing was similar but NOT THE SAME as the sensor in my S2000 engine.  And the temperature calibration was way off.

[BLKMGK]

Kripes guys, someone needs to get a pan of water, a good thermometer, some long wires, and a camp stove to just solve this the old fashioned way!

[westy]

"Kripes guys, someone needs to get a pan of water, a good thermometer, some long wires, and a camp stove to just solve this the old fashioned way!"  

I did.  The results are posted in the thread "Are all S2000 AIT sensors alike?" which, somehow, ended up on the Honda FWD forum.  Dare I say, "try a search?"  

[Mustangmick]

I'm new to this AEM.  I'm wondering if I have something connected wrong, or set up incorrectly in the software when getting the ETG sensor to work.

I finished connecting up all the wires, sensors, etc. and am in the process of testing everything out to see that it is working properly before I put the dash back together along with the car's interior.

I have the EGT model 30-2050, one wire connected to ground and the other to wire 61 EGT #1.  The resistance reads 222 ohms, the ambient temperature here in FL is about 84 or so in the garage.  The EGT 1 volts read 1.54 volts, the temperature reads 32 degrees F.  That matches up with the table that came with the sensor.  I wanted to calibrate this so it read correctly, went through the wizard, and all the things I could find in the software for setup, sensors, egt...

The table/chart shows egt volts as zero.   Where is that coming from?   The table seems to be adjusted from that voltage looking at the EGT paramaters chart.  It appears that EGT1-4 are 4 separate things and EGT volts is yet another.  Is there some place I am to define EGT volts as EGT1 since I have the EGT probe wire connected to wire 61?

[jtDevilDog]

By far the most common type of temp sensor used is the thermister type which is a resistor that changes is value based on the temperature. The calibrations usually supplied with these is resistance (Ohms) vs. temp. To convert this value into a voltage that can then be entered into the EMS calibration, use this equation:

EMS Volts = 5.00 * ( Resistance / ( Resistance + 2,200 ) )


This information does not apply to the EGT Inputs.

JR,

I have a control systems question. I am assuming that the EMS's I/O are voltage controlled/reference. The voltage/resistance conversion looks like an equation for an Op Amp configuration. If so, how is that configured and what is the difference air temp and EGT input circuits?

I'm not trying to get proprietary info, so be general if need be. I have just been wondering about instrumentation and control system applications.

Thanks
-Jason

[soundeffects]

So I'm trying to hookup my AIT sensor and my 5 bar map sensor. The AEM only has 1 input wire for both sensors, what do I do with the other 1-2 wires left on the AIT sensor wire harness and the 5 bar sensor harness??

I forget but one of the 2 sensors has 2 wires, so I would I assume one is the input to the EMS and the other is to a ground?

On the other sensor it has 3 wires, one input, one ground, one? This for my Toyota Supra Turbo by the way.