Red Lion GEARS - Manual (Page 2)

PITCH DIAMETER (P.D.) - The diameter of the circle described by the tooth-
to-tooth contact point when running in mesh with the teeth of another gear.
This point is roughly half way between the root (bottom) and the tip of the
gear tooth. The Pitch Diameter is slightly smaller than the outside diameter
of the gear.
DIAMETRAL PITCH (D.P.) - The number of teeth/inch of Pitch Diameter.
Thus a 20 D.P. gear has 20 teeth for each inch of Pitch Diameter. A 60-tooth,
20 D.P. gear would have a pitch diameter of 3', a 60T, 10 D.P. gear has a Pitch
Diameter of 6'.
PRESSURE ANGLE - Pressure angle relates to tooth shape and strength. It has
no significant effect on the operation of the gear for exciting magnetic
pickups, and pickups can be used with gears of any pressure angle.
OUTSIDE DIAMETER (O.D.) - The outside diameter is the overall diameter
of the gear to the tops of the teeth, and is used for calculating surface speed
when the gear is used to excite a magnetic sensor. The O.D. can be
determined from the following formula:
O.D. =
RPM x Nt
60
Example: A 60T, 16 D.P. Gear has an O.D. of:
O.D. =
10 x 60
3.1 x π = 3.875 inches
SURFACE SPEED - The output of a magnetic pickup depends on the linear
surface speed of the tops of the passing gear teeth. Surface speed is normally
expressed in inches/sec. and can be calculated for a given gear as follows:
Surface Speed in inches /sec. =
50 x 3.1 x π
60
or; RPM =
60 +2
20
Example: What is the surface speed of the 60T, 20 D.P. Gear when running
at 50 RPM? At what RPM will the 1-Volt Threshold Speed (10 inches/sec.)
for the MP-62TA be realized?
Gear O.D. =
Surface Speed x 60
O.D. x π
= 3.1" (From O.D. formula above)
Surface Speed =
RPM x O.D. x π
60 = 8.115 inches /sec.
1-Volt Threshold RPM (@ 10 in/sec.) =
60 + 2
16 = 61.61 RPM
OUTPUT SIGNAL FREQUENCY - The frequency generated by passing gear
teeth is related to gear RPM and the number of gear teeth (Nt) by the
following:
Output frequency (Hz or teeth/sec.) =
Nt(No. of teeth) + 2
D.P. (Diametral Pitch)
STANDARD SPUR GEAR DEFINITIONS, RELATIONSHIPS & FORMULA
Gear parameters are fundamentally related to their use as power transmission elements. Although these
parameters are not the most convenient when using gears to excite magnetic pickups, they can be easily converted
to more useful form, once the basic definitions are understood.
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