GMC Chevrolet Camaro 1998 Service Manual page 107

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General Information
Order
Order refers to how many times an event occurs
during one revolution of a rotating component.
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For example, a tire with one high spot would create a
disturbance once for every revolution of the tire.
This is called first-order vibration.
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An oval-shaped tire with two high spots would create
a disturbance twice for every revolution. This is
called second-order vibration. Three high spots would
be third-order, and so forth. Two first-order vibrations
may add or subtract from the overall amplitude of
the disturbance, but that is all. Two first-order
vibrations do not equal a second-order. Due to
centrttugal force, an unbalanced component will always
create at least a first-order vibration.
Vibration Diagnosis and Correction 0-95
Electronic Vibration Analyzer (EVA)
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The J 38792 Electronic Vibration Analyzer (EVA) is
specifically designed to diagnose vibrations. This
hand-held device is similar to a scan tool. A standard
12-volt power feed supplies the power. The vibration
sensor, or the accelerometer, is at the end of a
6 m (20 ft) cord. The vibration sensor can be mounted
virtually anywhere on the vehicle where a vibration
is felt.
EVA Basic Hookup
1. Inspect that the software cartridge is correctly
inserted at the bottom of the unit. (The cartridge
usually remains there at all times.)
2. Connect the vibration sensor cord into either
input A or B.
3. Line up the connector so that the release button
is at the bottom.
Important: Do not twist the connector. The sensor
should remain plugged into the unit at all times.
4. Push the connector into the input until the
connector clicks and locks in place.
5. Plug the power cord into a 12-volt power feed in
order to turn the EVA on. (There is no ON-OFF
switch.}
To Disconnect the sensor, press the release button
and gently pull the connector straight out.