Main Features & Specifications
3-digit LED display plus 7-segment
Linear display with 0-5V wideband range or 0-1V
Alternative display switching (A or B readings for
wideband values); petrol or LPG readings for narrowband
0V and 5V endpoint value limit adjustments for both A
and B displays.
Decimal point positioning.
Display leading zero
Bargraph can be operated in dot, bar or centred-bar
mode for wideband range. S-curve set-up allows for dot or centred bar
Display dimming with minimum brightness and dimming
Quieting period used for input measurement to ensure
Power Supply: 6-15V @ 240mA (full display brightness)
Input Current Loading: less than ±1mA
Digit Update Period: 250ms
Bargraph Update Period: 30ms
Wideband Display Reading Range: 0-999
Narrowband Display Reading Range: 11.8 to 20.6 for unleaded
petrol with the stoichiometric ratio set for 14.7; 12.6 to 21.4 for LPG with
stoichiometric at 15.5. The display shows an "L" for ratios below the lowest
value and an "r" for ratios above the highest value.
WHY WOULD YOU want to monitor the air/fuel ratio as you drive?
Well, for starters, it will allow you to save fuel since the display clearly
indicates when the engine is running rich.
When used in conjunction with a wideband oxygen sensor and
controller, the air/fuel ratios shown on this unit are more accurate than can be
obtained from the narrowband sensors that are typically used in cars and which
are really only accurate close to the "stoichiometric" point (ie, the air/fuel
ratio at which there is just enough oxygen in the air to ensure complete
Fig.1: here's how the display unit is used with a wideband sensor and its associated controller. The narrowband S-curve output from the controller is fed to the engine management computer (see text).
Under normal driving, most engine management systems operate
under "closed loop" control. This is where the air/fuel ratio from an oxygen
sensor is monitored and controlled by the car’s engine control unit (ECU) to
maintain a predetermined fuel mixture. This is usually stoichiometric but under
light cruise conditions the mixture can go
lean to improve fuel economy.
Conversely, during acceleration, the air/fuel mixture in many
cars is allowed to go rich to improve performance and is not under the control
of the ECU. This is called "open loop" and the richness of the mixture depends
on other factors such as the throttle setting and the injector opening