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APPENDIX E. DEFINITIONS
Follow Mode
A Configuration mode selectable item that allows the unit to continuously read opacity and maintain a “peak
hold” reading. The alternate mode is Test Series Mode.
Opacity
The percentage of light transmitted from a source that is prevented from reaching a light detector.
Preliminary Snap Acceleration Test
A series of Snaps (usually at least 3) performed before testing begins to clear the exhaust system of
residual particles.
Snap Acceleration Test
The engine is allowed to run at maximum RPM’s for 4 to 5 seconds and brought back to idle. Three “snaps”
are taken for this test. Each individual test is stored and a mathematical formula applied to provide an
“average.” See Page 14 for step-by-step instructions.
SAE J1667
A document created to outline specifications to manufacturers of opacity meters, as well as test criteria for
performance of opacity (smoke) readings.
Test Series Mode
A Configuration mode selectable item that causes the Model 6500 to run a fixed series of Snap
Acceleration Tests as dictated by the Society of Automotive Engineers (SAE) in specification J1667. The
alternate mode is Follow Mode.
