- •1.1 TODO LIST
- •2. PROGRAMMABLE LOGIC CONTROLLERS
- •2.1 INTRODUCTION
- •2.1.1 Ladder Logic
- •2.1.2 Programming
- •2.1.3 PLC Connections
- •2.1.4 Ladder Logic Inputs
- •2.1.5 Ladder Logic Outputs
- •2.2 A CASE STUDY
- •2.3 SUMMARY
- •2.4 PRACTICE PROBLEMS
- •2.5 PRACTICE PROBLEM SOLUTIONS
- •2.6 ASSIGNMENT PROBLEMS
- •3. PLC HARDWARE
- •3.1 INTRODUCTION
- •3.2 INPUTS AND OUTPUTS
- •3.2.1 Inputs
- •3.2.2 Output Modules
- •3.3 RELAYS
- •3.4 A CASE STUDY
- •3.5 ELECTRICAL WIRING DIAGRAMS
- •3.5.1 JIC Wiring Symbols
- •3.6 SUMMARY
- •3.7 PRACTICE PROBLEMS
- •3.8 PRACTICE PROBLEM SOLUTIONS
- •3.9 ASSIGNMENT PROBLEMS
- •4. LOGICAL SENSORS
- •4.1 INTRODUCTION
- •4.2 SENSOR WIRING
- •4.2.1 Switches
- •4.2.2 Transistor Transistor Logic (TTL)
- •4.2.3 Sinking/Sourcing
- •4.2.4 Solid State Relays
- •4.3 PRESENCE DETECTION
- •4.3.1 Contact Switches
- •4.3.2 Reed Switches
- •4.3.3 Optical (Photoelectric) Sensors
- •4.3.4 Capacitive Sensors
- •4.3.5 Inductive Sensors
- •4.3.6 Ultrasonic
- •4.3.7 Hall Effect
- •4.3.8 Fluid Flow
- •4.4 SUMMARY
- •4.5 PRACTICE PROBLEMS
- •4.6 PRACTICE PROBLEM SOLUTIONS
- •4.7 ASSIGNMENT PROBLEMS
- •5. LOGICAL ACTUATORS
- •5.1 INTRODUCTION
- •5.2 SOLENOIDS
- •5.3 VALVES
- •5.4 CYLINDERS
- •5.5 HYDRAULICS
- •5.6 PNEUMATICS
- •5.7 MOTORS
- •5.8 COMPUTERS
- •5.9 OTHERS
- •5.10 SUMMARY
- •5.11 PRACTICE PROBLEMS
- •5.12 PRACTICE PROBLEM SOLUTIONS
- •5.13 ASSIGNMENT PROBLEMS
- •6. BOOLEAN LOGIC DESIGN
- •6.1 INTRODUCTION
- •6.2 BOOLEAN ALGEBRA
- •6.3 LOGIC DESIGN
- •6.3.1 Boolean Algebra Techniques
- •6.4 COMMON LOGIC FORMS
- •6.4.1 Complex Gate Forms
- •6.4.2 Multiplexers
- •6.5 SIMPLE DESIGN CASES
- •6.5.1 Basic Logic Functions
- •6.5.2 Car Safety System
- •6.5.3 Motor Forward/Reverse
- •6.5.4 A Burglar Alarm
- •6.6 SUMMARY
- •6.7 PRACTICE PROBLEMS
- •6.8 PRACTICE PROBLEM SOLUTIONS
- •6.9 ASSIGNMENT PROBLEMS
- •7. KARNAUGH MAPS
- •7.1 INTRODUCTION
- •7.2 SUMMARY
- •7.3 PRACTICE PROBLEMS
- •7.4 PRACTICE PROBLEM SOLUTIONS
- •7.5 ASSIGNMENT PROBLEMS
- •8. PLC OPERATION
- •8.1 INTRODUCTION
- •8.2 OPERATION SEQUENCE
- •8.2.1 The Input and Output Scans
- •8.2.2 The Logic Scan
- •8.3 PLC STATUS
- •8.4 MEMORY TYPES
- •8.5 SOFTWARE BASED PLCS
- •8.6 SUMMARY
- •8.7 PRACTICE PROBLEMS
- •8.8 PRACTICE PROBLEM SOLUTIONS
- •8.9 ASSIGNMENT PROBLEMS
- •9. LATCHES, TIMERS, COUNTERS AND MORE
- •9.1 INTRODUCTION
- •9.2 LATCHES
- •9.3 TIMERS
- •9.4 COUNTERS
- •9.5 MASTER CONTROL RELAYS (MCRs)
- •9.6 INTERNAL RELAYS
- •9.7 DESIGN CASES
- •9.7.1 Basic Counters And Timers
discrete sensors - 4.19
ure 4.22. These values show the percentage of incident light on a surface that is reflected. These values can be used for relative comparisons of materials and estimating changes in sensitivity settings for sensors.
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Reflectivity |
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nonshiny materials |
Kodak white test card |
90% |
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white paper |
80% |
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kraft paper, cardboard |
70% |
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lumber (pine, dry, clean) |
75% |
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rough wood pallet |
20% |
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beer foam |
70% |
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opaque black nylon |
14% |
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black neoprene |
4% |
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black rubber tire wall |
1.5% |
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shiny/transparent materials |
clear plastic bottle |
40% |
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translucent brown plastic bottle |
60% |
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opaque white plastic |
87% |
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unfinished aluminum |
140% |
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straightened aluminum |
105% |
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unfinished black anodized aluminum |
115% |
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stainless steel microfinished |
400% |
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stainless steel brushed |
120% |
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Note: For shiny and transparent materials the reflectivity can be higher than 100% because of the return of ambient light.
Figure 4.22 Table of Reflectivity Values for Different Materials [Banner Handbook of Photoelectric Sensing]
4.3.4 Capacitive Sensors
Capacitive sensors are able to detect most materials at distances up to a few centimeters. Recall the basic relationship for capacitance.
discrete sensors - 4.20
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k = dielectric constant |
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A = area of plates |
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d = distance between plates (electrodes) |
In the sensor the area of the plates and distance between them is fixed. But, the dielectric constant of the space around them will vary as different materials are brought near the sensor. An illustration of a capacitive sensor is shown in Figure 4.23. an oscillating field is used to determine the capacitance of the plates. When this changes beyond a selected sensitivity the sensor output is activated.
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NOTE: For this sensor the proximity of any material near the electrodes will increase the capacitance. This will vary the magnitude of the oscillating signal and the detector will decide when this is great enough to determine proximity.
Figure 4.23 A Capacitive Sensor
These sensors work well for insulators (such as plastics) that tend to have high dielectric coefficients, thus increasing the capacitance. But, they also work well for metals because the conductive materials in the target appear as larger electrodes, thus increasing the capacitance as shown in Figure 4.24. In total the capacitance changes are normally in the order of pF.
discrete sensors - 4.21
electrode |
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metal |
electrode |
dielectric |
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Figure 4.24 Dielectrics and Metals Increase the Capacitance
The sensors are normally made with rings (not plates) in the configuration shown in Figure 4.25. In the figure the two inner metal rings are the capacitor electrodes, but a third outer ring is added to compensate for variations. Without the compensator ring the sensor would be very sensitive to dirt, oil and other contaminants that might stick to the sensor.
electrode |
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compensating |
Note: the compensating electrode is used for |
electrode |
negative feedback to make the sensor |
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taminations on the face of the sensor. |
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Figure 4.25 Electrode Arrangement for Capacitive Sensors
A table of dielectric properties is given in Figure 4.26. This table can be used for estimating the relative size and sensitivity of sensors. Also, consider a case where a pipe would carry different fluids. If their dielectric constants are not very close, a second sensor may be desired for the second fluid.
discrete sensors - 4.22
Material |
Constant |
ABS resin pellet |
1.5-2.5 |
acetone |
19.5 |
acetyl bromide |
16.5 |
acrylic resin |
2.7-4.5 |
air |
1.0 |
alcohol, industrial |
16-31 |
alcohol, isopropyl |
18.3 |
ammonia |
15-25 |
aniline |
5.5-7.8 |
aqueous solutions |
50-80 |
ash (fly) |
1.7 |
bakelite |
3.6 |
barley powder |
3.0-4.0 |
benzene |
2.3 |
benzyl acetate |
5 |
butane |
1.4 |
cable sealing compound |
2.5 |
calcium carbonate |
9.1 |
carbon tetrachloride |
2.2 |
celluloid |
3.0 |
cellulose |
3.2-7.5 |
cement |
1.5-2.1 |
cement powder |
5-10 |
cereal |
3-5 |
charcoal |
1.2-1.8 |
chlorine, liquid |
2.0 |
coke |
1.1-2.2 |
corn |
5-10 |
ebonite |
2.7-2.9 |
epoxy resin |
2.5-6 |
ethanol |
24 |
ethyl bromide |
4.9 |
ethylene glycol |
38.7 |
flour |
2.5-3.0 |
FreonTM R22,R502 liq. |
6.1 |
gasoline |
2.2 |
glass |
3.1-10 |
glass, raw material |
2.0-2.5 |
glycerine |
47 |
Material |
Constant |
hexane |
1.9 |
hydrogen cyanide |
95.4 |
hydrogen peroxide |
84.2 |
isobutylamine |
4.5 |
lime, shell |
1.2 |
marble |
8.0-8.5 |
melamine resin |
4.7-10.2 |
methane liquid |
1.7 |
methanol |
33.6 |
mica, white |
4.5-9.6 |
milk, powdered |
3.5-4 |
nitrobenzene |
36 |
neoprene |
6-9 |
nylon |
4-5 |
oil, for transformer |
2.2-2.4 |
oil, paraffin |
2.2-4.8 |
oil, peanut |
3.0 |
oil, petroleum |
2.1 |
oil, soybean |
2.9-3.5 |
oil, turpentine |
2.2 |
paint |
5-8 |
paraffin |
1.9-2.5 |
paper |
1.6-2.6 |
paper, hard |
4.5 |
paper, oil saturated |
4.0 |
perspex |
3.2-3.5 |
petroleum |
2.0-2.2 |
phenol |
9.9-15 |
phenol resin |
4.9 |
polyacetal (Delrin TM) |
3.6 |
polyamide (nylon) |
2.5 |
polycarbonate |
2.9 |
polyester resin |
2.8-8.1 |
polyethylene |
2.3 |
polypropylene |
2.0-2.3 |
polystyrene |
3.0 |
polyvinyl chloride resin |
2.8-3.1 |
porcelain |
4.4-7 |
press board |
2-5 |