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The Programmable Logic Controller (PLC) and Smart Roll work together to give the desired output . Typically the pulses from a Smart Roll
are read by a PLC and converted to a speed output . This speed output can then be used by the PLC to create actions, such as shutting
down a conveyor due to an under speed condition .
If the roll is rotating too fast or the PLC is not sampling often enough, the output will not work as desired . There are specifications you
will need to know about your conveyor setup, PLC, and Smart Roll sensor . These specifications are belt speed, outside diameter including
lagging of the Smart Roll, pulses per revolution of the Smart Roll, sampling rate of the PLC and/or the minimum sample duration, and
power supplied to the sensor from the PLC .
The Smart Roll sensor has a maximum switching frequency of 20 Hz, or 20 pulses per second . Digital electronic equipment, such as a PLC,
takes intermittent sensor readings rather than continuously monitoring the sensor . If the switching of the sensor pulses is faster than the
sampling rate of the equipment, errors may occur . Marginal cases may have erroneous speed output from missed pulses, and extreme
cases may cause a complete lack of output .
WHAT IS A PULSE?
As the roll rotates, it opens and closes an electrical circuit to create pulses a preset number of times per revolution . One pulse is defined as
one complete on/off cycle .
Examples:
6 pulses per revolution the sensor creates 6 on/off cycles, or pulses for each revolution .
2 pulses per revolution the sensor creates 2 on/off cycles, or pulses for each revolution .
1 pulse per revolution the sensor creates 1 on/off cycles, or pulses for each revolution .
The 1 and 2 pulse options have fewer pulses and greater pulse duration, i .e . the pulse will have a greater width on the chart . Figures 6 .1 and
6 .2 show pulses using 400 feet per minute belt speed, Smart Roll part numbers SAD5CSRSB-1PL4, and SAD5CSRSB-2PL4 respectively .
WHAT IF THE PULSES ARE TOO FAST FOR MY ELECTRONICS?
USING A PLC
Figure 6 .1: Example sensor output for a 1 pulse roll,
P/N SAD5CSRSB-1PL4
Figure 6 .2: Example sensor output for a 2 pulse roll,
P/N SAD5CSRSB-2PL4
