Innovate Motorsports LMA-3 - Manual (Page 17)

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6.5 Using the RPM-Converter with pulsed RPM input (Tach) signals
- Unplug the inductive clamp from the LMA-3 if connected.
- Connect the RPM signal to the CH1+ input screw terminal.
The decimal point of the digit display of the LMA-3 should light up steadily. This indicates when a
valid rpm signal is detected. If it does not light up, check your connections.
DO NOT CONNECT A PULSED RPM SIGNAL TO THE INDUCTIVE CLAMP INPUT. THIS
MIGHT DAMAGE THE LMA-3 OR LM-1.
7 Measuring Pressures
The LMA-3 has a built in MAP sensor. To use it, connect a small ¼” hose between a
vacuum/boost connection AFTER the throttle body and the LMA-3 MAP input port.
It should be connected after the throttle body because the lowest pressure that can be measured
before the throttle body is atmospheric pressure (discounting some pressure losses from the
intake tract before the throttle body).
MAP stands for Manifold Absolute Pressure. This means that the sensor measures pressure
referenced to absolute vacuum, not atmospheric pressure like many vacuum and boost gauges.
Engine parameters like fueling, ignition timing, compressor efficiency and so on are dependent
on the MASS of air (in pounds per cubic foot or kg per cubic meter) entering the engine. As air is
a gas, it’s mass is dependent on it’s ABSOLUTE pressure, referenced to absolute vaccuum and
it’s temperature.
Most vaccuum and boost gauges are gauge pressure sensors. A gauge pressure sensor
measures the difference to atmospheric pressure, not the absolute pressure. So, without knowing
atmospheric pressure at the point where the sensor gets it from, the actual air-mass entering the
engine can’t be measured. Because the atmospheric pressure changes with altitude and
weather, the gauge pressures are not a precise metric. This is specially problematic for boost
pressure sensors, because their atmospheric reference source comes typically from inside the
cabin or engine compartment. The atmospheric pressure there can change with speed from
aerodynamic effects (ram pressure).
7.1 Measuring MAP
Function 1 of input 4 of the LMA-3 measures absolute pressure with a range of 0..1 bar (0..14.7
PSIa). This is the range intended for normally aspirated engines where the maximum intake
pressure can be atmospheric pressure.
Function 2 of input 4 of the LMA-3 measures absolute pressure with a range of 0..3 bar (0..44.1
PSIa). This is the range intended for boosted engines where the maximum intake pressure can
be up to 29.4 PSI above atmospheric pressure.
7.2 Measuring boost/vaccum
The LMA-3 can use it’s MAP sensor also as gauge pressure sensor if so desired. As stated
above, this is NOT the preferred way of measuring pressures, but it is possible. The LMA-3 will
measure the current atmospheric pressure in the intake tract when it starts up and stores this