RAC Plus User’s Manual
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Chapter 1 — Introduction
How do they work?
To use the RAC Plus I or Plus II DMI to accurately measure distance, either
a modular distance sensor (MDS) or mechanical transmission sensor is
used to send pulses to the DMI. The Quick-Kit, which is a modied version
of the MDS, can also be used.
Most newer vehicles (1992 and newer) have an electronic distance/speed
sensor inside the transmission which sends pulses to the vehicle's on-
board computer for use in the speedometer, ABS braking system, engine/
transmission control, etc. These vehicle-generated signals can be as many
as 100,000 pulses per mile, which is far more than the RAC needs to ac-
curately measure distance. Further, since the vehicle manufacturers are not
concerned with accurate distance and speed readings at very low speeds
(your speedometer may not move below 5 mph), the signal strength at these
low speeds is extremely minimal.
The MDS is not just an improvement over other electronic interface type
sensors. First, and foremost, its proprietary circuitry allows more accurate
slow speed measurements by sensing signals as low as 10 Mv from the
vehicle speed sensor. Second, it is designed to be mounted under the ve-
hicle dashboard rather than under the hood as with other interface sensors.
This gets the MDS out of a severe heat and moisture environment and into
a more controlled environment. Third, our exclusive internally generated
Sensor Test and Tap Test features allow the user to verify proper sensor and
instrument operation. Finally, the modular design simplies installation.
Older vehicles with mechanical speedometer cables use the mechanical
transmission sensor, which is screwed on to the transmission. For infor-
mation on how to install this type of sensor, refer to the instructions that
came with the sensor.
The next chapter details how to install a modular sensor into your vehicle.
If your already have a sensor installed, you may skip to Chapter 3 for infor-
mation on calibrating your RAC.
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