Networks and I/O Exam
ME 486, Fall, 2006 (Open book)
Name________________________
(20) 1. Mark True (T) or False (F) as the best answer for each of the following statements:
a.
Ethernet is a bus network that can be distributed hierarchically.
T_X F___
b.
IEC 61131-3 defines 5 programming methods for programming logic control.
T_X F___
c.
CAN uses the three lowest OSI layers.
T___ F_X_
d.
Profibus uses a bus communication network.
T_X_ F___
e.
In ladder logic the ladder rungs are processed vertically down and left to right.
T_X_ F___
f.
Foundation fieldbus is the dominant fieldbus in Europe.
T___ F_X_
g.
IEEE 1394 network can be extended to 24 km.
T___ F_X_
h.
An instruction list is one approach to logic programming.
T_X_ F___
i.
The logic control method uses asynchronous process control methods.
T_X_ F___
j.
The signal output from the sensor to the PLC is called PLC output.
T___ F_X_
(40) 2. Construct the ladder logic diagram for the robot interlock system in Example 8.1 of the text (see
page 258). Use the assigned variables shown on page 262.
Solution:
Let
X1 = workpart present (1) or not (0)
X2 = press cycle completed (1) or not (0)
X3 = part removed from die (1) or not (0)
Y = Begin loading sequence (1) or wait (0)
X1
X2
X3
Y
Grading:
1. Selection of variables
2. Diagram
20 pts
20 pts
(40) 3. An industrial furnace is to be controlled as follows:
 The contacts of a bimetallic strip inside the furnace close if the temperature falls below the set
point, and opens when the temperature is above the set point.
 The contacts regulate a control relay that turns the heating elements of the furnace on and off.
 If the door to the furnace is opened, the heating elements are temporarily turned off until the
door is closed.
Considering the process:
a) Specify the I/O variables for this system operation and define symbols for them (e.g., X1,
X2, C1, Y1 – remember that we use X’s for inputs and Y’s for outputs or states).
b) Write logical statements using if, then, else, or, and, and not constructs in proper sequence
with the defined variables to program the logical flow of the control process.
c) Construct the ladder logic diagram for the system.
Solution:
a) Let
X1 = temperature below setpoint (1) or not (0) – normally open
X2 = door closed (1) or not (0) – normally open
Y = Furnace relay on (1) or wait to activate relay (0)
b) If X1 and X2, then the furnace is turned on (because the relay will activate the heating elements).
Alternatively stated….if the temperature falls below a setpoint, then the bimetallic strip will close,
and if the door is closed, current will flow to activate a relay that turns on the heating elements of the
furnace, i.e., furnace on. Current will flow through the bimetallic strip and also through the door
closed switch to activate the relay.
c)
X1
X2
Y
Grading:
1. Selection of variables
2. Logical statement
3. Diagram
10 pts
10 pts
20 pts