Monarch Instrument Nova Strobe DB Plus - Manual (Page 8)

user to multiply the initial flash rate by 2, 3, 4, 5, etc up to the maximum flash rate, which is
very helpful on fan blades. Using this feature, one can superimpose the blades on top of each
other and check for blade tracking, bent blades, lead and lag tests, etc. For example: with a 3
bladed fan spinning at 3600 RPM and the strobe flashing at 3600 FPM, press the Alt button to
turn on the Alt chevron. Now turn the knob clockwise 2 clicks. The strobe is now flashing at
10,800 FPM (effectively 3600 times 3) and the fans blades will be all superimposed on each
other. You can now see if the blades are out of alignment, bent, etc. by viewing the blades from
the front or from the edge.
The FPM/FPS button toggles the display between Flashes Per Minute(FPM) and Flashes Per
Second (FPS). The FPM and FPS chevrons on the display indicate how the flash rate is
being displayed.
NOTE: The unit automatically converts between FPM and FPS, so you can set the rate in
FPM and then view it in FPS by simply pressing the FPM/FPS button.
The Store button stores the current flash rate into the last preset location the user has viewed.
The View button displays the next flash rate preset (one of six). It does not change the flash
rate. This allows the user to select which preset to write over before storing the current flash
rate by pressing the Store button.
3.4 Power Up Features
Press and hold one of the buttons listed below, then turn on the strobe by using the
trigger switch:
The Store button will restore the factory programmed preset flash rates: 100, 500, 1000, 3600,
7200 and 14000 FPM.
The Alt Function button will turn on all the display segments for two seconds and then show
the software revision, “REV x.x”.
4.0 USING THE STROBOSCOPE TO MEASURE RPM
The primary use for a stroboscope is to stop motion for diagnostic inspection purposes. However,
the stroboscope can also be used to measure speed. In order to do this, several factors need to be
considered. First, the object being measured should be visible for all 360° of rotation (e.g. the end
of a shaft). Second, the object should have some unique part on it, like a bolt, key way or imperfection
to use as a reference point. If the object being viewed is perfectly symmetrical, then the user needs
to mark the object with a piece of tape or paint in a single location to be used as a reference point.
Look only at the reference point.
If the speed of rotation is within the range of the stroboscope, start at the highest flash rate and
adjust the flash rate down. At some point you will stop the motion with only a single image of the
object in view. Note that at a flash rate twice the actual speed of the image you will see two images.
As you approach the correct speed you may see three, four or more images at harmonics of the
actual speed. The first SINGLE image you see is the true speed. To confirm the true speed, note
the reading and adjust the stroboscope to exactly half this reading, or just press the ÷2 button. You
should again see a single image (which may be phase shifted with respect to the first image seen).
For example, when viewing a shaft with a single key way, you will see one stationary image of the
key way at the actual speed and at 1/2, 1/4, etc, of the actual speed. You will see 2 images of the
key way at 2 times the actual speed, 3 key way at 3 times, etc. (see Figure 5). The FPM equals the
shaft’s Revolutions Per Minute (RPM) at the highest flash rate that gives only one stationary image
of the key way.
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Figure 5 Object Rotating at 3500 RPM
If the speed is outside the full scale range of the stroboscope (14,000 FPM), it can be measured
using the method of harmonics and multipoint calculation. Start at the highest flash rate and adjust
the flash rate down. Be aware that you will encounter multiple images. Note the flash rate of the
first SINGLE image you encounter, and call this speed “A”. Continue decreasing the flash rate until
you encounter a second SINGLE image, and note this speed as “B”. Continue decreasing the speed
until you reach a third SINGLE image at speed “C”.
For a two point calculation the actual speed is given by:
RPM = AB/(A-B)
For a three point calculation:
RPM = 2XY(X+Y)/(X-Y)2 where
X = (A-B) and
Y = (B-C)
If a Remote Optical Sensor or Magnetic Sensor is used to sense one pulse per revolution (External
mode), the readout will display directly in RPM (FPM) without any adjustment required.
In instances when you can shut down the device and install a piece of reflective tape, then an optical
tachometer is easier to use for RPM measurement. Stroboscopes should only be used when you
can’t shut down the device. The human eye is not easily tricked into seeing a stopped image by
a stroboscope when the flash rate is slower than 300 FPM. Therefore, stroboscopes should not be
used below 300 FPM for inspection or to measure RPM.
5.0 LAMP AND FUSE REPLACEMENT
5.1 Lamp Replacement
WARNING: Before attempting to remove the lamp, make sure the stroboscope
is turned off and any mains cord is removed from the AC outlet.
Allow the lamp to cool waiting at least 1 minute.
The stroboscope is designed to discharge the internal high voltages within 30 seconds. However,
caution should be exercised when replacing the lamp.
The lamp can be replaced by using just a pocket screwdriver. It is not necessary to remove
any screws to replace the lamp. A new spare lamp is supplied with each new DA+ or DB+
Strobe Kit.
To change the lamp:
1.
Push apart the two tabs on the side of the reflector housing and remove the front lens
using a small screwdriver to help pry one tab and lift the lens. Take care not to pry the tab
any more than is necessary to free the lens. The reflector is held in place by the front lens
and will come loose, but is not necessary to remove the reflector.
2. Hold the lamp with a cloth between your forefinger and thumb and rock it back and forth
gently while pulling out. Do not attempt to rotate the lamp. The lamp is socketed and
will come out easily when pulled.
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Stopped Image 1/4 times 1/2 times 1 time 2 times 3 times 4 times
Flash Rate (FPM) 875 1750 3500 7000 10500 14000