When the %O
2
in the exhaust surrounding a sensor exceeds 19.5%, the AFRecorder will
automatically change from displaying that sensor's AFR to %O
2
. This allows for the fast
visual checking of the AFR measurement calibration when the engine is stopped and the
exhaust contains pure air. When the engine is restarted, the AFRecorder will automatically
change back to displaying AFR in the programmed units.
The Average Deviation of AFR (DEV) is the average percentage change in the measured
AFR in 0.01 seconds. It is defined as:
DEV
AFR AFR
AFR
ii
i
n
i
i
n
=
−
×
−
=
=
∑
∑
1
1
1
100
where AFR
i
is the current AFR, AFR
i-1
is that sensor's AFR 0.01 seconds earlier, and n is the
number of measurements. The greater "DEV" gets, the "rougher" the measured AFR is.
Once the AFRecorder has begun displaying the AFR measurements, only two keys will alter
its operation: "SYS" (System) and "REC" (Record). The outcome of pressing "REC" will be
discussed in the section entitled Recording on page 14. Pressing "SYS" presents the main
menu on the left display (see Figure 2). Subsequent menu-related displays appear on the left
display.
MAIN MENU
1 MEASURE 4 OFFSETS
2 RESULTS 5 AIR CAL
3 SETUP 6 ENABLE
Figure 2: Main Menu (accessed by pressing "SYS")
From the main menu, the user can command the continuation of the measurement and
display of parameters (select "1 MEASURE" by pressing "1" on the keypad), the review of a
recorded session (select "RESULTS"), the modification of the AFRecorder's configuration
(select "SETUP"), or the modification of the AFR measurement function (select "OFFSETS",
"AIR CAL", or "ENABLE"). Figure 3 shows the "tree" of sub-menus below the main menu.
Using the keypad, the user can move within the tree and make selections.
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