Calibration for analog sensor (voltage, resistance and NTC sensors)

[ArT]

There is new version of calculator for scaling (calibration) analog sensors:

UTCOMP v3.5+ calculator: https://1drv.ms/x/s!AsGCGuEkUvVGsDN4JGd ... L?e=vRmTca
UTCOMP v3.4 (and older) calculator: https://www.dropbox.com/s/cjpidy5gf90hhe2/NTC.xls?dl=0

Sheet includes calculators for:

• NTC analog temperature sensors,
• voltage (linear) sensors (e.g. for MAP sensor, AFR controller etc.)
• resistance (linear) sensors (e.g. for pressure 0-10 bar sensor)

Thanks to calibration process, there is possibility to connect almost any analog sensor to UTCOMP achieving high accuracy of readings. Maybe it looks complicated at the beginning, but trust me, it's NOT. I'll help you if you have any issues.

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For analog temperature sensors (NTC) two constants are needed: R25 and Beta (three constants for older versions: A, t, t0).
For analog linear sensors (voltage or resistance) you will need two constants (a and b).

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In order to calibrate sensors connected to AdcX input, you will need only data table with voltage<->readings.

In order to calibrate sensors connected to AdcVccX input, you will need data table with resistance<->readings or voltage<->readings (if you connect sensor you can read voltage at sensor in utcomp app). If you have only resistance data that you will need also two constants: (1) value of pull-up resistor in UTCOMP (Rpullup) - it's equal to 1000 Ohm (+/- 0,1%) for UTCOMP-3 and UTCOMP-PRO; (2) value of voltage reference for analog circuit (VREF) - typical values are 5.0, 5.2 or 5.4 volts - you can read VREF in "Readings" tab in UTCOMP app (since version 3.1, in older versions it was always 5.0 volts). Every UTCOMP-PRO is stock calibrated to achieve best accuracy, so everyone can have slightly different VREF value.
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Please feel free to ask in this thread if you have any questions about scaling and calibration analog sensors.

[nwuser1]

Hi,

What behind the NTC sensors constants A, t, t0, what tey mean?

Thanks!

[ArT]

A, t and t0 are constants for equation described in Appendix A (page 45):
http://www.reveltronics.com/downloads/u ... manual.pdf

[nwuser1]

I have sensor points like: +2C = 4V ; +7C = 3,5V ; +90C = 1,2V
How I`ll know the constants? I tried to find out them by excel: http://reveltronics.com/downloads/adds/NTC.xls
but when I put them into utcomp, results were terrible..
Can You help, please?

[ArT]

You will need more data. I recommend you to make voltage reading every few degrees or find sensor specification in ohms.

[amirtiti]

hi
I'm in a middle of a installation process
And i want to know more about the calibration of the NTC sensors

What exactly is the effect of each one of the constants (A, t, t0) i tried to change them in the calculator you provide but it is frustrating to just try some numbers
Can you please explain it in more detail?

[ArT]

These values are constants in equation for exponential approximation.
Equation formula is on page 45:
http://www.reveltronics.com/downloads/u ... manual.pdf

As you can see T0 is temperature offset. A and t are exponential constants.
You can also use some kind of math software (e.g. origin 7.5 demo) to get best calculation.

Please note that it is almost impossible to get accurate approximation in full range of temperatures. Usually for NTC sensors you need to limit range to 50-120C or 60-150C to get accurate readings in specified range.

[amirtiti]

great
thank you

[Daily_Driver]

Is it possible to piggyback off factory sensors (coolant temp and oil pressure) so I have both factory gauge and UT Comp? My shop manual does not list temperature/pressure values for the senders, instead listing gauge readings (low, normal, high) at certain ohms. I found some data for replacement senders such as these:
Pressure:
10 PSI: 45-55 Ohms or Open,
40 PSI: 40-50 Ohms
90 PSI: 35-40 Ohms

Temperature:
100º F 1425 ohms
220º F 147 ohms

[ArT]

In most cases it is possible, but if you do not have exact data then you should measure it yourself.
Voltage level on sensor you can read directly from UTCOMP - just connect sensor to any AdcX input and read voltages in "readings" tab. You will need also temperature/pressure for specified voltage - you should use other measurement device to check it. If you have linear sensor (most pressure sensors) than you will need only 2 data points. If you have not linear sensors (eg. stock analog temperature sensors) than you will need many points - I recommend to get each point every 2-5 degrees to get reasonable accuracy in scaling.