Jamar RAC-100, Manual

Page: 13 / 56

2-5
Chapter 2 — Installation
voltage fluctuations from Turn Signals, Brake Lights, etc. Plug the power
cable into the hole labeled Power on the MDS, as shown in Figure 2.4.
A diagram of the complete installation for the MDS is shown in Figure 6
on page 2-6.
Adjusting the Vehicle Speed Sensor Pulse Rate
The signal pulses coming from the vehicle speed sensor are generated for
use by the vehicle’s computer, engine/transmission control, fuel manage-
ment, ABS brakes, etc. The pulse rate can vary from 4,000 to in excess of
100,000 pulses per mile. The MDS will
condition and amplify these pulses for
use by the DMI. Since the higher pulse
rates are not required for accurate dis-
tance measurements, the MDS incor-
porates a divider circuit to reduce the
pulse rate. This is done by adjusting
the rotary switch on the front of the
MDS, as shown in Figure 2.5.
Although your particular vehicle may vary, generally Chrysler and Ford
vehicles use a 4 to 1 ratio (position 4 on the switch) while General Motors
vehicles use a 16 to 1 ratio (position 16 on the switch). To adjust the ratio,
use a small screwdriver to rotate the switch until the slot in the switch
points to the desired ratio. Note that when the switch is turned counter-
clockwise until it stops, it is at the 1 to 1 ratio.
The adjustments go from 1 to 1 (1 pulse into the sensor, 1 pulse out) through
64 to 1 (64 pulses into the sensor, 1 pulse out). The Tap Test positions are
explained in the troubleshooting section on page 3-4. You may need to
adjust the ratio again based on the results of the calibration procedure de-
scribed in Chapter 3. Any time you change the pulse ratio, you will need to
re-calibrate the DMI.
Once you have installed the MDS, install your RAC 100 or 200 using the
instructions on page 2-7.
Figure 2.5
Rotary Switch Adjustment