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When ECU is purchased with 1,2 or more (4 or 6 is sometimes requested, some logger was ordered and delivered with 8 EGT inputs),
- EGT amplifier outputs are connected to inputs with no pullup
Confirmed:
- it was the internal ecu pull up
- 51K (really ? Usually 2k7 pullup on analog inputs)
Unfortunately NO input with no pullup resistor in this ECU.
- is there a way to scale it mathematically based on the pull up?
- yes, since the function is monotone, it is possible to calculate.
The EGT amplifier 5V output has a protection equivalent to
- 1 / (1/75+1/100) = 42.86 k Ohm resistor
- 2.7 / ( 2.7+42.86) = 0.0593 ... this means 2k7 pullup causes a strong bias, and resolution is reduced
- say 20C => 1102 C (at 0.02V measured on the 0-11V output )
- say 1170C => 1170C (at 5V)
- The theoretical formula for that case is:
- EGTconv1=1170 - (1170-20)/(1170 - 1102) * (1170 - EGT)
- EGTconv1=1170 - (1170-20)/(1170 - 1102) * (1170 - 1147) = 781 C for example
- Note: this is rough estimate, not based on actual measurement or calibration.
- even if calibrated, the scaling would be rather rough.
Best to use input with no pullup.
- input with 2k7 pullup will likely make the EGT reading granularity annoyingly rough
- reasonable formula (VT ini can be tweaked to output real calibrated result) becomes possible if
Connecting the analog input (with internal 2k7 pullup) via/to:
- 6k3 to the 0-11V output of the EGT amplifier
- 4k7 "pulldown" to GND
- this way it acts like output divider with effective of 2k7=1/(1/6.3 +1/4.7) which means that half of the range is available, which allows precise measurement after simple calibration.
- Something like 2*EGT-1170 conversion will be sufficient and good granularity:
- 0C => 585C (2.5V on input) => 0C
- 1170C => 1170C (5V) => 1170C
Orig report:
Engine off, ambient sensor temp (~20C)
- Tested Pin7 DVM output (1V/100°C) and getting 0.7 volts
- corresponding to 70C
- not 6 volts, roughly corresponding to Pin6 2.5 volts.
- I'm getting 2.5 volts out of Pin6 (0-5V output, 1V/233.3C)
- Thus getting 580°C instead of 20°C.
Hint: The output is almost certainly connected to an input with pullup (possibly strong pullup).
- Diagnostic: disconnect anything from output, and measure DC voltage with DVM (the DVM has 1 to 10MOhm input impedance).
- Solution: make sure to connect pin6 output to an input without pullup resistor
Sensor connection (seems good):
EGT sensor is K type yellow-red wires:
- yellow = green (plus wire) to board GND
- red = white (minus wire) to the board cathode on corner