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Appendix B
Variable Speed Tachometer
Applications involving a variable speed product and
requiring automatic contaminant rejection must use
a tachometer. The tachometer monitors product
speed and provides this information to the MPC.
The user has much flexibility in the choice of the
tachometer. It can be any device which monitors
product speed and provides a digital signal to the
MPC with the following characteristics:
Voltage Output
Logical 0 — 0.0 - 0.7 VDC
Logical 1 — 4.0 - 35 VDC
Or NPN Open Collector
Current Output
Source N/A
Sink 1mA min.
Maximum Frequency
50 Hz
Minimum Positive Pulse Width
5 msec.
Minimum Negative Pulse Width
5 msec.
The tachometer can be a photo-electric device, Hall
effect device, proximity sensor, programmable
controller, etc.
The tachometer is often a stand-alone device which
attaches directly to a conveyor shaft or has a wheel
which rides directly on the conveyor belt or pulley.
The device which attaches directly to the end of a
pulley shaft is recommended because those which
depend on friction to drive a wheel may slip and
therefore provide inaccurate information. It is
normally best not to use the driven pulley since it
may slip and thus cause inaccurate measurements.
An important factor to consider in the design of a
tachometer system is the resolution of the separate
digital pulses. The MPC can store up to 1200 pulses.
Thus if the Travel Distance (from the center of the
metal detector to the center of the reject device) is
36" the resolution of each bit in the shift register is
.030". Usually the total number of bits in the shift
register far exceeds the requirements of the
application. The normal procedure is to design a
convenient tachometer system and adjust the MPC
for the number of pulses needed for proper reject
distance.
TACHOMETER SYSTEM DESIGN
Design a tachometer system with the following
characteristics:
Resolution: 1.5 inches or better.
Maximum Belt Speed: 200 ft./min.
Travel Distance (from MPC to Reject Device):
6 ft. = 72"
Tachometer Drive Pulley Diameter: 3"
1.
The tachometer will be attached to the shaft of
the 3" diameter pulley so the tachometer shaft
will rotate at the same velocity as the pulley. Cal-
culate the minimum number of tachometer pulses
per revolution to provide the specified 1.5 inch
linear resolution.
a. Calculate linear belt travel distance per revo-
lution of the tachometer drive pulley. This is
simply the circumference of the pulley.
D = 3.14 X 3 inches = 9.42 inches per
revolution
b. There must be 1 tachometer pulse every 1.5
inches. Calculate the minimum number of
pulses per revolution.
(1 pulse / 1.5 inches) X (9.42 inches / rev) =
6.28 pulses / rev
Содержание E-Z TEC IV
Страница 58: ...58 Figures cont Figure 5 Detect Modes...
Страница 59: ...59 Figures cont Figure 6 E Z Tec Major Components Figure 7 E Z Tec Power Supply Analog Version Shown...
Страница 60: ...60 Figures cont Figure 8 Metal Free Area Figure 9 Typical Conveyor Showing Intermittent Current Loops...
Страница 62: ...62 Figures cont Figure 12 Metal Detector Mounting Feet Figure 13 Conveyor Belt Splices...
Страница 63: ...63 Figures cont Figure 14 Electrical Connections...
Страница 64: ...64 Figures cont Figure 15 Analog Version Control Panel...
Страница 67: ...67 Figures cont Figure 19 Flowchart of MPC Menu Structure...
Страница 85: ...85 Appendix C cont Vertical Reject Units Figure C2 E Z Tec IV and V Vertical Reject Sensing Head...
Страница 88: ...88 Appendix D cont Slim Tec Single Surface Units Figure D1 E Z Tec IV and V SlimTec Single Surface Schematic...
Страница 93: ...93 Figure E2 E Z Tec IV and V SlimTec Aperture Metal Free Area Appendix E cont Slim Tec Aperture Units...
Страница 96: ...96 Appendix F cont VFS Packaging Machine Metal Detectors Figure F1 VFS Metal Detector Schematic...
Страница 97: ...97 Appendix F cont VFS Packaging Machine Metal Detectors Figure F1 VFS Metal Detector Metal Free Area...
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