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Both proximity and photo-electric devices are
available in a slot sensor type construction, which can
be mounted to sit astride the disk. If this technique is
used the disk should be slotted rather than drilled.
Disc Construction
The disk diameter and number of holes/slots can be
determined when the required shift distance of the
speed sensor is known (see following section). If the
required shift distance is 25mm/shift then the hole/slot
pitch of the disk should be designed so the sensor
gives one pulse cycle out for 25mm moved by the
conveyor, see Figure A-2 below.
Hole Pitch = 6.283 x radius / number of holes
Fig 25 Disc Construction
In building the disk, make sure that the solid and gap
width are such as to keep the pulse width and
frequency within the specified limits.
Determining The Required Shift Distance
Of The Speed Sensor
The speed sensor provides digital pulses in relation to
the distance moved by the conveyor. The incremental
distance moved between pulses is known as the
SHIFT distance and is the smallest interval
measurable by the detector (i.e. its resolution).
Table A-1 can be used to determine the shift distance
for your system. Using distance, d, between the
detection and rejection points
110
(see Figure A-3 below), follow these steps.
Fig 26 Determining The Required Shift Distance
1)
Find the point on the table where d lies
between the minimum and maximum limits. If
this value lies at more than one point in the
table select the point that corresponds to the
smallest shift distance,
Example.
For, d = 1000 mm (39 inch)
This value lies at four points in the table,
which corresponds to shift distances of
13 mm, 19 mm, 25.5 mm and 32 mm.
Select the smallest value, 13 mm (0.5 inch).
2)
Next check that your maximum conveyor speed
does not exceed the limit specified in the table.
Example.
For, d = 1000 mm (39 inch) and,
Shift Distance = 13 mm (0.5 inch)
The maximum conveyor speed is 38
m/min (125 ft/min).
APPENDIX A
4618-021
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