Chapter 10 Exercises

Exercises

1. When dealing with machinery, continued motion and stopping are at issue. With a
   continuous process, stopping and _________ are at issue. Failsafe deals with _________
   while fault tolerant deals with _________ _________.
2.  “Good for detecting clear materials in close spaces
   • Good in detecting shiny objects or vibrating objects”:
   • Name the type of photo-eye that has these characteristics:
3. Using both Siemens and A-B Ladder, write the program that will produce the following:
4. Using both Siemens and A-B Ladder, write the program that will produce the following:What is this called?
5. The two pictures below may be labeled either Fail Safe or Fault Tolerant. Write in the appropriate response in the two boxes below.
6. Write the code to convert an input that is 0 to 10 V representing a signal 0 to 250 gal/min
   using both Siemens and A-B input channels.
7. How would one check for validity of the signal or an over-range/valid condition for
   Siemens? For A-B?
8. From lab 10.3, write the code to calculate calories using the two inputs for voltage and
   current.
9. From lab 10.1, finish the code for a four-digit tws representing a number from 0-9999
   with the diodes pointing to the right (true high representation).
10. Give a simple way to find the average scan time without writing a program.
11. How fast can the program of Lab 10.1 be safely executed?

Lab 10.1 Multiplexers

Note: Lab 10.1 requires that code is executed too fast to be viewed on the on-line monitor. Timing diagrams will have to be drawn to successfully complete this lab. The figure below shows the thumbwheel switch as it is supposed to be used. This lab uses the same switch but is wired in the reverse direction due to the direction of the diodes.

The Thumb-Wheel Switch pictured at left shows a thumb-wheel switch as used in
industry. The tws has been used in factories to enter numbers into computers and plcs. The switches show the number on the face and give the BCD bits shorted in the switch as the number is entered.

For instance, if the number displayed is 3 , the bits associated with the 1 bit and the 2 bit are shorted giving 24 V on these pins with 0 v on the 4 and 8 bit pins.

For instance, if the number displayed is 6 , the bits associated with the 2 bit and the 4 bit are shorted giving 24 V on these pins with 0 v on the 1 and 8 bit pins.

Likewise, if the number displayed is 9 , the bits associated with the 1 bit and the 8 bit are shorted giving 24 V on these pins with 0 v on the 2 and 4 bit pins.

For the BCD (Binary Coded Decimal) number above, if the four inputs were connected to the Siemens processor’s inputs I0.0, I0.1, I0.2 and I0.3 and the word representing the tws number was stored in the variable ‘num’, the following program would be generated to move this single digit into the integer number ‘num’.

This lab requires the student to use the thumbwheel switches to enter a number from 0 to 9999 into an internal memory location (integer). The number is the one represented on the thumb wheel switches (TWS’s) and can be changed. The internal memory location should be updated at least each half second.

With the tws above, we notice the diodes pointing to the right. This is the direction of positive current flow. We notice in the figures below the tws’s with diodes shown in the reversedirection. This is due to the idea that tws’s can be constructed with the diodes pointing either way. If pointing to the right, the wiring is for true high logic. If to the left, the wiring is for true low logic. However, one can still read the tws in the true low switch using true high logic if the bits are scanned one bit at a time through each tws. This is what is required in this lab assignment.

Allow only 4 inputs and 4 outputs to the PLC from the TWS’s