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This page describes every electrical detail
about the AFM-1 instrument. It helps to shine a better
light on the internal operations and it's dynamic
behavior. Since we mentioned already all the general
info in earlier pages, here we go. 16 bit CPU (Infineon C164CI) @ 20 MHz, 128 kByte
Flash, 8kByte SPI EE-memory,128 kByte
All analog measurements are based upon a 10-bit ADC
resolution (1024). For noise and component drift
reasons, the typical accuracy is 8-bit (0.25 % of full
scale).
The sampling rate for all eight channels is
600 Hz (base sample rate). Multiplexed channels are
processed in sequential order.
1) I-Pump circuit data (air fuel circuit)
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I-pump current sensing resistor R11 = 61.9 %
U11.A gain (LSU-4 config) = 8.5
Current sense range = 588 mV = 5 V / 8.5 ==>
9.5mA = 0.588 / 61.9
valid lambda range (0.70 to 2.42) = 3.25 mA=
-1.85 mA to +1.40 mA
valid lambda resolution = 350 = 1024 / (9.5 /
3.25) ==> 0.005 = (2.42 - 0.70) / 350
valid lambda accuracy = measured lambda +/-
0.02 assuming 0.005 * 4
AF-ratio accuracy = measured gasoline
AF-ratio +/- 0.15 <== ((20.6 - 10.8) / 350)
* 4
typical lambda or AF ratio accuracy = 1.5 %
of full scale (1.5 <== 1.14 = 4 / 350)
Throughout our calculations we usually round down the
results like 1.5 <== 1.14 (bigger number = less
accurate = down) to accommodate the non
linearity of the IP-current to lambda sensor
curve. |
2) I-Pump PID control loop
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V-sense input gain = 4
V-sense input resolution = 1.22 mV = 5.0 V
/ (1024 * 4)
14 bit I-Ppump pwm controlled output (7-bit hi
and 7-bit low) at 19.2 kHz pwm period
All calculations are performed with 32-bit
integer arithmetic.
The I-Pump PID control loop executes as a timer
controlled ISR at 600 Hz. |
3) Heater PID control loop
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V-sense Ri circuit 3.3 k Rref over 80 Ohm
Vs.Ri ==> 3380/80 = 1024 /24 ==> 24 count
6-bit Heater pwm controlled output at 37.5 Hz
pwm period
All calculations are performed with 32-bit
integer arithmetic.
The Heater PID control loop executes as a timer
controlled ISR at
37.5 Hz.possible future changes : To improve
the 80 Ohm control resolution (currently 24 ADC
steps) the 3.3 k Rref (R18) could be
changed to the 2.2 k (36 count). This impacts
the specification under item 2.7 in the Bosch
specs. AC load <= 250 uA. |
4) Auxiliary inputs 0 to 5 V
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Three inputs with over-voltage protection through clamping
diodes to 0V and 5V with 10 k input series input
resistor and 0.1 uF filter caps to ground.
input voltage range = 0.0 to 5.0 V.
input impedance > 10 k
Sampling frequency = 150 Hz (600 / 4)
10-bit ADC resolution (1024) = 5 mV / step.
8-bit ADC typical accuracy = 0.25 % of full
scale or +/- 20 mV. |
5) Auxiliary inputs -50 to +75 mV
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Due to the nature of this multiplexed
differential input circuit, there is no over
voltage protection circuit available.
Eight amplified differential inputs with gain of
40, zero offset of 50 mV and 100 k input
impedance. Each input circuit has 10 k series
resistors with a 0.1 uF filter cap.
differential input voltage range = -50 mV to +75
mV
common mode range = 2.0V +/- 1.5V
input impedance = 100 k
Sampling frequency = 75 Hz (600 / 8)
10-bit ADC resolution (1024) = 0.125 mV ==> 3.4
deg C @ K-thermocouple
8-bit ADC typical accuracy = 0.6 mV ==> 15 deg C
@ K-thermocoupleA zero offset compensation is
available for each individual channel by
software. |
6) RPM input circuit
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This circuit provides auto-gain input
voltage control.
Input range = 10 to 450V DC.
minimum pulse period = 100 us
minimum pulse width (pos) = 50 usA ringing
timeout window is programmable in software. |
7) O2 sensor simulation outputs
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Two pwm controlled analog outputs, 12-bit at
600 Hz period.
Output voltage range 0.0V to 5.0V.
Output sink/source impedance 100 Ohm series
current limiting resistor. |
8) power supply specs
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AFM-1 control circuit : 10 V to 16 V at 250
mA
LSU-4 sensor heater : 10 V to 16 V at 5 A max (pwm
peaks) |
All specifications are subject to change without
notice.
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