Innovate Motorsports ST-12 - Manual (Page 19)

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5.2.10 Using the RPM-Converter with pulsed RPM input (Tach) signals
- Unplug the inductive clamp from the ST-12 if connected.
- Connect the RPM signal to the CH1+ input screw terminal.
The decimal point of the digit display of the ST-12 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 ST-12 OR LM-1. Again, this should just result in an error code, not mechanical
damage.
5.3 Measuring Pressures
The ST-12 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 ST-12 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 vacuum and it’s temperature.
Most vacuum 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).
5.3.1 Measuring MAP
Function 1 of input 4 of the ST-12 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 ST-12 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.
5.3.2 Measuring boost/vacuum
The ST-12 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 ST-12 will measure the current
atmospheric pressure in the intake tract when it starts up and stores this value internally until it is started