Four things must be remembered when the expanded
scales are used:
1. The setting of the OFFSET controls is arbi-
L@INPUT SIGNAL OF
trary! Any segment may be chosen. However, only 42.000 RPM
segments which include the input signal are useful.
2. The letter system is a guide to help find the
segment which includes the input signal. It is not
exact. The actual setting may be as much as two
letters away f rom the indicated setting; especially
on the X3 scale. This is normal. It does not affect
instrument accuracy.
3. The numbers on the meter scales do not in-
dicate specific speeds because the segment can be
set anywhere along the basic range. However, if
OFFSET CONTROL SET TO
the selected segment includes the input signal, CORAESPONOINC LETTER
the pointer indicates the relative position of the - BEFORE EXPANDING
input signal within the segment. If the segment
does not include the input signal, the pointer will
LD-Y-146
be off scale.
4. Calibration of the meter scales is determined Figure 2C-3. Using Offset Letter System
by the position of the pointer, the basic range
selected, and the degree of expansion. For example,
if the 60,000 range is expanded X3, the 0-2 scale
becomes a 20,000 rpm segment of the 60,000
range. If the pointer is placed over the 1.8 marker
by the OFFSET controls, and it subsequently moves
to the 0.4 marker, a 14,000 rpm decrease in the POSITION Of METER
POINTER REPRESENTS
input signal is indicated.
The following paragraph describes the use of the WITH POINTER AT 1.
ZERO REPRESENTS 2 REPRESENTS
expanded scale by following through a differential 32,000 RPM
52,000 RPH
measurement example.
2C-4 EXAMPLE PROCEDURE
a. Connect the Model 500C to proper souy6e; turn
on the power switch and allow five minutes for the
instrument to reach a stable operating temperature.
Q. Q.
b. Make an unexpanded measurement of the input
OFF OFF
signal as described in paragraph 2C-2. Assume that
the measurement is 42,000 rpm on the 60,000
range, and that *6000 rpm variation is to be
observed. Note that the meter pointer rests be-
tween D and E on the letter system. See Figure
2C-3.
RANGE
RPM
c. Adjust coarse OFFSET control to the corres- 60.000
ponding point between D and E on the letter system
around the control.
d. Place EXPAND switch to X3 position. With the
EXPAND switch in the X3 position, the 0-2 scale
is a 20,000 rpm segment of the 60,000 range.
Figure 2C-4. Using "1" as A Reference (0-2
Scale). 60,000 Range Expanded X2
e. Refine OFFSET adjustment to place pointer at
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