BRUEL & KJAER 4912 Instruction Manual page 5

USES:
• Inspection of rotating or
reciprocating machinery
• Mode study vibration
testing
• Loudspeaker analysis
• Dynamic field balancing of
rotating parts
• Speed/frequency
measurement of rotary,
linear or vibratory motions
• Investigation of high-speed
repetitive industrial
processes on the shop
floor
FEATURES:
• Combined motion analyzer
and tachometer
• Internal frequency
generator range 5 to
1 25
Hz
(300
to
7500
r/min)
The Type 491 2 Portable Strobo-
scope is a compact hand-held instru-
ment which combines the function
of tachometer with that of motion
analyzer . It permits both qualitative
investigation and accurate measure-
ment of various kinds of rapid, repet-
itive motion in trouble-shooting and
design and development situations .
The Stroboscope utilizes the phen-
omenon of persistance of vision to
"freeze" or slow down motion of vi-
brating, rotating or reciprocating
parts of machinery too rapid for the
Fig.1 . Photoelectric Probe MM 0012
19-126
• Flash rate obtainable O to
130 Hz (0 to 7800 r/min)
• Tachometer operation 5 to
1500
Hz
• External trigger range Oto
20000 Hz
• Constant white light
output independent of
frequency above 25
flashes per second
• 4-digit liquid crystal
display of frequency or
r/min
• Compact self-contained
unit for use in the hand
• Minimum
2,5
hours'
operation off built-in
accelerated-charge
rechargeable NiCd
batteries
• Mains or external DC
operation when required
unaided eye to perceive . When the
machinery is illuminated by the
flashing light from the xenon lamp
in the Stroboscope and the flash
rate is suitably adjusted, the illusion
obtained is of stationary or slowly
moving machinery. This illusion
makes it very easy to assess qualita-
tively how the machinery is behav-
ing, and it also permits comparative
measurements to be made on the
amount of motion taking place .
Since the 491 2 features a 4-digit
liquid crystal display which can be
set to read either Hz or r /min, it
can also be used to measure accu-
rately the rate or frequency of the
motion (to the nearest r / min or
0, 1 Hz).
Fig.2. Magnetic Transducer MM 0002
type
4912
Portable
Stroboscope
The 491 2 can be used as a ta-
chometer or a combined tachome-
ter / stroboscope, as well as a free-
running stroboscope. In the free-
running mode the lamp is triggered
from an internal frequency-genera-
tor which may be adjusted between
5 and 1 25 Hz by means of a 1 0-
turn knob . The actual frequency is
indicated on the display .
The 491 2 can be triggered exter-
nally, via a coaxial cable, from a
photoelectric tachometer probe (e.g.
B & K MM 0012, Fig . 1), a magnetic
probe (e.g. B
& K MM
0002, Fig.2),
a vibration meter (e.g. B & K Type
2511), or a variety of other motion-
sensing devices or instruments.
When it is used solely as a tachome-
ter, the display will indicate fre-
quency
from 5 to 1 500 Hz or the
equivalent r / min . If the upper limit