Innovate Motorsports ST-12 - Manual (Page 24)

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The range of frequencies that the ST-12 can measure can be programmed by with LM Programmer. The
ST-12 can be set to any frequency range between 0 and 10 Hz for the full 0..5V range to 0..15 kHz for
the full 0..5V output (logging) range.
Also, LM Programmer has convenient conversions built in, so you don’t have to calculate the resulting
frequency ranges for speed sensing or RPM sensing yourself. See chapter 10.x for details.
A frequency input signal must have an amplitude (voltage range of pulse) between 0.5V at the low pulse
point to minimum of 3V and maximum of 40 V at the high pulse range.
NOTE:
The custom RPM feature will work only for even fire tach signals, not for tach signals that vary
their time between pulses during an engine cycle. Use the input 1 RPM functions instead.
5.6 Measuring duty cycle
To measure the duty cycle of a signal (on any channel except channel 2), the input signal must cover the
same voltage range as for a frequency signal. Duty cycle is defined as the ratio between the time a signal
is active and the total time of the active and inactive time. A signal can be either active high ( the event,
like injector open, happens when there is a high voltage) or active low (the event happens when the
measured signal is at ground or close to it).
Very often the injector duty cycle is to be measured by the ST-12. A typical fuel injector is connected to
12V on one side, while the other side is connected to ground when the ECU opens the injector. Because
the pulse is therefore active when the voltage on the pin is at ground, negative duty cycle is measured.
So called peak-hold injectors (as opposed to saturated injectors), work differently. Their drive signal first
goes to ground for a high current opening pulse, then rises to 8-10 Volts for the hold period. Because the
ST-12 sees everything above 2.5V as “high”, it will be able to see only the peak period. On some peak-
hold systems it is possible to connect the CHx+ input of the ST-12 to 12V at the injector and connect the
CHx- input to the injector signal to still measure correctly. But that is not always the case. The LogWorks
2.0 Manual shows an alternative method. If the above method works, it actually measures positive duty
cycle.
6 Programming the ST-12
To connect the ST-12 for programming follow these steps:
1. Disconnect all LC-1STs.
2. Connect the 2.5mm to DB 2 computer interface cable into the Serial OUT port. Your computer
needs a serial port. If it does not have one, you will need a USB to serial adapter.
3. Switch the power on the ST-12
4. Start the LM Programmer application
The following screen will show up: