122-28176 Parallax Inc, 122-28176 Datasheet - Page 122

• Manufacturer Part Number: 122-28176
• Description: GUIDE STUDENT PROCESS CONTROL
• Manufacturer: Parallax Inc

Specifications of 122-28176

• Accessory Type: Manual
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: Propeller Education (PE) Kit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

Parts Required
Same circuit as Activity #2
Excessive Signal Durations
When dealing with the physical world and human-input, most things never go as planned,
but a well-programmed process control system should be able to deal with these mishaps.
As the boxes make their way down the conveyor, it is likely that problems will eventually
occur. A box will possibly jam as the diverter shifts. What will our indication be of a
problem? Someone on the docks telling us they aren't getting boxes? The controller can
be made sophisticated enough to detect when a box is present for too long, shutdown the
conveyor, and sound warnings.
The current program is using flags to indicate when a box is detected. It is set repeatedly
as the program keeps sampling. An accumulator with the following capabilities can be
used to keep track of how many times the box has been detected.
What's an appropriate critical value? It depends on the sampling rate. For example, if a
box requires 4 seconds to pass the beam and the program is sampling every ½ second, a
normal accumulated value may be 8. The critical value should be at least twice this.
will need to implement these steps:
To add code to detect and respond to a box detection signal of excessive duration, we
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As the box is detected, a variable is incremented by one with each scan of the
input.
If the accumulator reaches a critical value (10?), the system is shut down and
warnings issued.
If no box is detected the variable is reset to zero.
Create a variable to hold an accumulated value.
Add code to add one to the variable whenever a box is detected.
Add code to zero the variable when the box is not detected.
Add code to shut down the conveyor and sound an alarm if the accumulator
reaches an excessive value. A good StampPlot alarm can be implemented using:
DEBUG "~PWAV nralarm",CR