Section 3: Installation 3-15
70055MP Revision D February 3, 2000
3. Calculate the Voltage Drop Resistor value (Rd):
Rd = Rs x 1.4.
4. Select a voltage drop resistor as follows:
Resistance: first standard value greater than the Rd.
Power rating: 2 watts.
Tolerance: 5% or less
As an example, consider a potentiometer with thirty-two 40 ohm
resistors. The calculated string resistance would be:
Rs = (40 ohms) x (32 Resistors) - 1280 ohms.
And
Rd = Rs x 1.4 = 1280 x 1.4 = 1792 ohms.
The next standard resistor value greater than 1792 is 1800 ohms.
Therefore, the selected voltage drop resistor should be an 1800 ohm,
5%, 2 watt resistor.
Connect the wires to the OEM Potentiometer as follows:
1. Connect the designated positive point lead to the OEM Potentiometer
Positive Point.
2. Connect the designated common point lead to the OEM Potentiometer
Common Point.
3. Connect the designated wiper lead to the OEM Potentiometer Wiper.
Connect the wires to the circuit board as follows:
1. Connect one end of the Voltage Drop Resistor (Vd) to a sensor power
supply terminal.
2. Connect the positive point lead to the other end of the Voltage Drop
Resistor (Vd).
3. Connect the common point lead to the designated Sensor Common
terminal.
4. Connect the wiper lead to Sensor Input #8.
NOTE: Tap Position must be calibrated to operate correctly (see Calibrate
Tap Position).
CAUTION: The positive lead must be connected to Sensor Input #5 and the
negative lead to Sensor Common. Failure to comply can damage the LTC-
MAP.