AFM-1 description

AFM-1 instrument info

For hardcore technical details follow the link to the AFM-1 hardware specifications
and click on AFM-1 software interface for the Windows instrument control application.

AFM-1 wideband air/fuel meter top view

AFM-1 wideband air/fuel meter side view 1
side view shows auxiliary
I/O connector

AFM-1 wideband air/fuel meter side view 2
O2 sensor connector and
two mV I/O connectors

The Air Fuel Meter also called a Lambda Meter facilitates precise Air Fuel measurements by using a Wide Band exhaust gas Oxygen sensor from Bosch (LSU-4).
For numerical output the air fuel or lambda ratio is displayed on a large 3 1/2" digit backlit LCD display.
The instrument is also supplied with a programmable 3 colored dual intensity 12 LED bar-graph for monitoring the dynamic variation of the air fuel ratio during the different engine load situations.
The fuel type and it's ratio is selectable for most common fuel types, including custom ratios.
Up to 12 auxiliary inputs are available to monitor additional engine parameters and to display them in numerical as well as graphical form on a MS-Windows based computer.
This computer can also be used to provide real-time data logging of all inputs during an engine run.
Two fully programmable analog O2 simulation outputs can be used to partially control a stock fuel injection unit and / or drive other indicators or instruments.
The power inputs provide individual 12Vand Ground connections for the control unit and the sensor heater.
The accuracy and dynamic response of the instrument is achieved by two control loops :
Constant Nernst-Cell impedance through PID control of the sensor heater temperature.
Ion Pump Current PID control loop based upon a 14 bit PWM output control signal .
Both control loops are implemented in 16/32 bit integer arithmetic, executing at 37.5 Hz.

We use a 16-bit microcontroller designed for control applications (Infineon C164CI) and precision rail to rail OP-amps (Texas Instrument TLV2474A).

1) Lambda Sensor (UEGO type)

bosch lsu-4 wideband oxygen / lambda sensor

The instrument uses a Bosch LSU-4 type Wide Band exhaust gas Oxygen sensor. This sensor is factory calibrated and used in a variety of European cars (past 1999). A sensor can be either purchased from Micro-Craft or other suppliers and most likely any Bosch LSU-4 type sensors will work with the instrument, provided the user also acquires a mating connector and connects it to the interface cable.

The Lambda Sensor range is from 0.68 to 1.40 lambda ratio,
which relates to an air to gasoline ratio of 11 to 19.

UEGO stands for Universal-Exhaust-Gas-Oxygen sensor.

2) Auxiliary Inputs

One RPM input is provided with a dynamic range from 12V to 400V connected to a crank shaft sensor or the primary side of the ignition coil. The pulse to RPM ratio has a wide range of programmability.

Three 0 to 5V inputs are provided for signals like Throttle-Position-Sensor, Manifold-Absolute-Pressure, Mass-Air-Flow, or any signal within the 0 to 5V specifications. The software provides several scalability and calibration functions. A regulated 5V sensor supply output with 25mA is also supplied.

Eight -50mV to +75mV inputs are provided for individual exhaust gas temperature monitoring, that can be useful for some specific engine diagnostic information (K-type Thermocouple).
These inputs are also software scaleable to your particular sensor application.
Some of these inputs can possibly be used for strain gauge applications.

Individual 10V to 16V power and ground inputs for the main control circuit and the sensor heater supply allows for more flexibility with your particular application. However, in most cases the pos-supply inputs and grounds will be connected together.

3) Auxiliary outputs

Two analog outputs are provided to facilitate programmable O2 sensor simulation or be used to drive external analog instruments, gauges or indicators with more than 1000 Ohms of input impedance.

A regulated 5V output with a drive capability of 25mA is provided as a supply source for some of the various external sensors.

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