Innovate Motorsports LogWorks 3 - Manual (Page 141)

LogWorks3_Manual_1.01.doc - 141 -
kPa = atmospheric pressure (in millibar) * 0.1 - measured pressure (mmHg or Torr) * 7.5
15.3 Measuring voltages higher than 5 Volt
Because the Innovate Motorsports devices are designed for the common 0..5V sensors, their
input range is limited to 0..5V.
A simple voltage divider can reduce the measured voltage by a certain ratio, determined by the
divider ratio, which is in turn dependent on the values of the resistors used as divider.
Alternatively a potentiometer can be used. Recommended is a 100 kOhm potentiometer. The
advantage of a potentiometer is that ANY ratio can be simply dialed in.
The following shows a simple potentiometer circuit:
The 1 kOhm resistor (1/8 Watt or more) and the Zener diode (1/10 Watt or more) are for
protection of the LMA-2 or LMA-3 in case the input voltage is too high and the output of the circuit
exceeds 5.1V.
Potentiometers have typically 3 pins. The middle one is the slider (indicated with an arrow or
pointer in the schematic). The other two can be connected either way as in the schematic.
To calibrate, connect the point “Measured Voltage” to the car battery and measure the voltage
between the slider of the potentiometer and ground. Also measure the battery voltage.
The divider ratio is then:
Ratio = Battery voltage / slider voltage