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Subpage of MembersPage/WolfTm Summary: The '''100C/V (0-11V) output of the [https://shop.vems.hu/catalog/4xegt-amplifier-dsub9-p-186.html EGT amplifier] can be used with some care''', if the ECU was not ordered with the sufficient number of EGT inputs or analog inputs without pullup. See "GOOD granularity" below. ---- 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: * after the home-install, the cause of the '''higher reading was the internal ecu pull up''' ** 51K (really ? Surprisingly weak pullup. Which input ? Usually strong, 2k7 pullup on analog inputs, or no pullup at all.) ---- '''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. However... '''Rough granularity/resolution''' The EGT amplifier (internal voltage divider for convenience =) 233C/V (= also called "5V output") has an output protection equivalent to * 1 / (1/75+1/100) = 42.86 k Ohm resistance ** 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 granularity would be rather rough. Best to use input with no pullup. * input with 2k7 pullup will likely make the EGT reading granularity annoyingly rough, above. ---- '''Achieving GOOD granularity, using the 100C/V (= also called 0-11V) output and 2 resistor voltage divider:''' * 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: * '''5.3k to the 100C/V (pin7: 0-11V) output of the EGT amplifier''' (since the traditional EGT amplifier has 1k resistor on pin7 100C/V output: 1k+5.3k = 6.3 kOhm in the calculation). * '''4k7''' "pulldown" to GND This acts like 0-11V => 2.5 - 5V output divider * note: 6k3 and 4k7 effective resistance: 2k7=1/(1/6.3 +1/4.7) which means that half of the voltage range is available, which allows precise measurement after simple calibration. ** Something like '''2*EGT-1170''' conversion will be sufficient (refine it at least with the low temperature reading) and good granularity: ** 0C => '''585C''' (2.5V on input) => '''0C''' ** 1170C => '''1170C''' (5V) => '''1170C''' Needless to say: '''take care when using the 100C/V output, do NOT short to GND or 12V''' (only connect to the 1 end of the 5.3k resistor, use heatshrink, do not leave it uninsulated). * when using a DVM to measure voltage of the 0-11V output, make sure the DVM is in DC voltage mode (not current mode, which shorts the signal to GND, and might cause damage) ---- '''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
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