Page 280 - Electromechanical Devices and Components Illustrated Sourcebook

242 Electromechanical Devices & Components Illustrated Sourcebook

Range Sound Level Meters
Power
Readout
Switch
Various industrial, public address, theater, and home audio
applications can benefit from the ability to gauge the output
100K 1Meg level of sound producing equipment. To accomplish this, a
1K 20 Meg On
sound level meter, as shown in Figure 13-63, is commonly
used. These instruments consist of a microphone, amplifier,
INPUT Off
RANGE
and readout packaged in a single unit. The readout is in deci-
bels (dB). Most sound level meters are also equipped with a
fast/slow response switch and A and B weighting selector.
Input
The range is selected until the needle is as near to zero as
Figure 13-61 Frequency Counter possible. The value off zero is either added or subtracted
from the selected range value to provide the sound level.

Insulation Testers (Meggers)
Microphone
Insulation testers, or meggers as they are sometimes referred to,
are used to test and verify the effectiveness of electrical insula-
tion and isolation. These units have a high-voltage generator and
a meter that displays the leakage of the voltage across the insu-
lation being tested. The leakage can be directly converted into
ohms and the gauge will normally read in megohms. Figure 13-
62 shows a typical insulation tester. It should be noted that while Battery Test
Button
crank sets are quite common; these instruments are also avail- BATT
able with battery powered high-voltage supplies.
RANGE OFF 60 Range
120 70 Selector
110 80
Case 100 90

Scale 3 4 5 6 7 Output
2 8 Crank Handle
0 1 9 10 Weighting A SLOW
Meter 10 20 30 40 50 60 70 80 90 100 Selector C FAST
Mega Ohms
Response
WEIGHTING RESPONSE
Time
0
2 2
4
6 4
Leads dB Meter 10 BATT 6
− dB +

Figure 13-62 Insulation Tester (Megger) Figure 13-63 Sound Level Meter