PRACTICE PROBLEMS

(Note: Problem solutions are available at http://sites.google.com/site/automatedmanufacturingsystems/)

1. Analog inputs require:

a) A Digital to Analog conversion at the PLC input interface module

b) Analog to Digital conversion at the PLC input interface module

c) No conversion is required

d) None of the above

2. You need to read an analog voltage that has a range of -10V to 10V to a precision of +/-0.05V. What resolution of A/D converter is needed?

3. We are given a 12 bit analog input with a range of -10V to 10V. If we put in 2.735V, what will the integer value be after the A/D conversion? What is the error? What voltage can we calculate?

4. Use manuals on the web for a 1794 analog input card, and describe the process that would be needed to set up the card to read an input voltage between -2V and 7V. This description should include jumper settings, configuration memory and ladder logic.

5. We need to select a digital to analog converter for an application. The output will vary from -5V to 10V DC, and we need to be able to specify the voltage to within 50mV. What resolution will be required? How many bits will this D/A converter need? What will the accuracy be?

6. Write a program that will input an analog voltage, do the calculation below, and output an analog voltage.

7. The following calculation will be made when input A is true. If the result x is between 1 and 10 then the output B will be turned on. The value of x will be output as an analog voltage. Create a ladder logic program to perform these tasks.

8. You are developing a controller for a game that measures hand strength. To do this a START button is pushed, 3 seconds later a LIGHT is turned on for one second to let the user know when to start squeezing. The analog value is read at 0.3s after the light is on. The value is converted to a force F with the equation below. The force is displayed by converting it to BCD and writing it to an output card (force_display). If the value exceeds 100 then a BIG_LIGHT and SIREN are turned on for 5sec. Use a structured design technique to develop ladder logic..

9. A machine is connected to a load cell that outputs a voltage proportional to the mass on a platform. When unloaded the cell outputs a voltage of 1V. A mass of 500Kg results in a 6V output. Write a program that will measure the mass when an input sensor (M) becomes true. If the mass is not between 300Kg and 400Kg and alarm output (A) will be turned on. Write a program and indicate the general settings for the analog IO.

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