Operation While Charging; Accelerated Charging; External Power; Free-Running Stroboscope Operation - BRUEL & KJAER 4912 Instruction Manual

3.2.2. Operation while Charging
The 4912 cannot be operated while connected to the battery charger unless the 7-pin
DIN plug is modified as follows. Slide back the plastic sheath round the plug and remove
the two parts of the metal screen. To free the sheath it may be necessary to depress the
metal key visible through a window in the side of the sheath. The 491 2 may then be op-
erated whether or not the modified plug is pushed into the POWER INPUT socket for re-
charging, provided the batteries are not completely exhausted to begin with. When the
Stroboscope is operating at more than about 20 flashes per second, it drains more cur-
rent from the battery than can be supplied from the ZG 0113 (which is intended only for
charging, not for powering). However, the use of the ZG 0113 during operating can
greatly extend the operating-time of the 491 2 between charges.
3.2.3. Accelerated Charging
The rapid-charge batteries of the 491 2 may be completely recharged from exhaustion in
7 hours if a charging source of 600 mA is provided. The required voltage at this current
is 15 V. Neither figure should be exceeded. The charge source positive should be con-
nected to pin 3, and negative to pin 2, at the POWER INPUT connector (see Fig.2.2).
3.2.4. External Power
The 491 2 may be powered from a 6 to 1 5 V supply connected to POWER INPUT with
positive to pin 1 and negative to pin 2, whether or not the batteries are being charged at
the same time. The maximum power consumption varies from 1 W at 6 V DC to 5,5 W
at 1 5 V DC with tacho-only operation, and from 7 W at 6 V DC to 1 5 W at 1 5 V DC with
stroboscope operation. The 491 2 is protected against accidental reverse connection of
the external power source.
Type 2808 Power Supply, available separately, may be used to operate the 491 2 while
at the same time recharging the batteries from exhaustion in about 1 O hours to full
charge. To do this, connect the Type 2808 to a suitable mains supply as described in its
instruction manual, connect its OUTPUT socket to POWER INPUT on the 491 2 using
cable AO 0035 and set the CHARGE switch to "On".
3.3. FREE-RUNNING STROBOSCOPE OPERATION
The Stroboscope lamp will begin flashing at a rate determined by the setting of INTER-
NAL GENERATOR as soon as FUNCTION SELECTOR is set to "Int. Gen.", unless BAT-
TERY LEVEL indicates that there is insufficient supply voltage for proper operation. The
pointer leans to the right when the voltage is sufficient. If it does not, recharge the bat-
teries or provide a suitable external power source as described in section 3.2.
\
To obtain a stationary or slowly moving image of a rapidly moving object, first ensure
that the object is illuminated mainly by the light from the Stroboscope. Fig.3.1 and Table
3.1 show the characteristics of the beam from the lamp. Set INTERNAL GENERATOR to
its maximum clockwise position, and turn it gradually anticlockwise while observing the
object. This procedure will initially result in multiple images (unless the frequency of mo-
tion is very high) as the flash rate of the Stroboscope passes through synchronism with
the harmonics of the motion frequency of the object. The first stationary imagine which
is not in multiple occurs when the flash rate and the motion frequency are identical;
they may be read off the FREQUENCY indicator. To obtain the desired form of indication
(Hz or r/min), set FREQUENCY SELECTOR as preferred.
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