BRUEL & KJAER 4915 - Photoelectric Tachometer Probe MM 0012

3.3.2. Photoelectric Tachometer Probe MM 0012
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The Photoelectric Tachometer Probe MM 0012 is a combined infra-red source and pickup
device. It is designed for contact-free sensing of reflective objects, contrasting marks
etc., and together with the 4913 may be used as an external trigger source. For connect-
ing MM 0012 to the EXT. TRIGGER INPUT of the 4913 it is supplied with a 3 m long,
double-screened BNT Cable AQ 0158, which is used to carry the trigger signal as well as
the
necessary supply voltage for powering the Probe.
770521
Fig. 3.3. Photoelectric Tachometer Probe MM 0012 plus associated
dimensions
To trigger with the probe make a contrasting mark approximately 5 mm wide on the side
of the object to be examined and mount the Probe at a distance of 1 to 10 mm away from
the mark (see Fig. 3.4). With shiny objects use matt black adhesive tape or a black
marking pen for making a contrasting mark, while with non-reflective objects reflective
tape should be used. On each pass of the mark, the Probe will trigger the Stroboscope in
synchronism with the fundamental or sub-multiple of the motion frequency of the object.
If correct triggering cannot be obtained and the TRIGGER ERROR LED of the 4913
remains lit even when the TRIGGER LEVEL knob is set for maximum input sensitivity, the
Probe should be moved closer to the object. Alternatively, the effective output of the
Probe may be increased using a battery powered torch to illuminate the contrasting mark.
To prevent the Lamp Unit interfering with operation, avoid aiming its light beam directly
at the Probe, and/or screen the front of the Probe using a piece of black tape.
Fig. 3.4. The Photoelectric Tachometer Probe MM 0012 in use