automation book v6

8/11/2019 Automation Book V6

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AUTOMATIONENGINEERING

I dedicate this text to my students

They are my source of inspiration since I could

not find a text that cover the principles of

system integration applied to industrial controls

and automation

By:

Wence pez

Version 0.6

San Juan, Puerto Rico


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Prof. Wence Lpez Page 1 of 45 Version 0.6

Table of Contents

Chapter 1 Relay Logic ........................................................................................................2

Chapter 2 Sensors ...............................................................................................................3

Chapter 3 PLC Hardware ...................................................................................................9

Chapter 4 PLC Memory Map ...........................................................................................12

Chapter 5 Basic SLC Instructions ....................................................................................16

Chapter 6 Program Control...............................................................................................26

Chapter 7 Data Management ............................................................................................30

Chapter 8 Managing Files ................................................................................................35

Chapter 9 Special Addressing...........................................................................................42

Chapter 10 Introduction to Electro-Pneumatic ...................................................................43

Sample Documentation ............................................................................................ Appendix A

Laboratory Documentation ...................................................................................... Appendix B


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Automation Engineering Chapter 1


Chapter 1Relay Logic

Relay- It is an electromechanical device that consists of a coil and sets of hard contacts (metal tometal). When a voltage is applied to the coil, its contacts switch position, the open contacts

closed and the closed contacts opens. The relay can be used to interface high current loads and

various voltages levels. It is limited by relatively slow switching speeds and finite mechanicallife.

Complementary outputThe dual configuration of a sensing device, where one output is normally open and the other is

normally closed. An example is a SPDT form 1C relay contact.

SPST is an abbreviation for Single Pole Single Throw. It refers to a switch or a relay contact

(electromechanical or solid-state) with a single contact that is either normally open or normally

closed.

SPDT is an abbreviation for Single Pole Double Throw. It refers to a switch or anelectromechanical relay having one set of form 1C contacts. One contact is open when the other

is closed (complementary switching).

DPDT is an Abbreviation for Double-Pole Double-Throw. It refers to a switch or an

electromechanical relay with two sets of single-pole double-throw form 1C contacts that areoperated simultaneously by a single action (when the relay is energized).

SPDTSPST


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Chapter 2Sensors

2.1 Photoelectric sensors

There are 4 basic components to any photoelectric sensor:

a-

Light sourceb- Light detectorc- Lenses

d- Output device

The light source or emitter normally is a light-emitting diode (LED) that is a solid-state

semiconductor that emits light when current is applied. The LEDs emits a specific wavelengths

or colors of light. The most common light sources are infrared, visible red, green, & blue.

Different LED colors offer different characteristics, therefore the color can be used as anadvantage to detect specific object.

The light wavelengths of the Infrared LEDs are greater than 800 nanometers (800 Angstroms)and are invisible to the eye and safe to most photographic films. Infrared is the most efficient

since they generate the most light & least heat. They are used where maximum light output is

required. Visible red is used where a visible beam is required to help a setup. Visible red, blue

& yellow LEDs are used in applications where specific colors or contrasts must be detected.

One of the biggest advantages of an LED is its ability to be modulated. Modulating an LED

simply means turning it ON and OFF at high frequencies. The photo detector and its amplifierare turned to the modulation frequencies. Only the modulated light is amplified and all other

light that reaches the phototransistor is ignored. This is analog to a radio receiver, which tunes

only one station and ignores the others. Modulation of sensors allow them to be used in a more

wide variety of places, like areas with dust, smoke, fog, mist, etc.

Non-modulated receiver may be used to detect parts that emit their own light (i.e. Red-hot metal,

room lighting).

The light detector or receiver normally is a photo detector that detects the incoming light to the

sensor. A typical photo detector is a photodiode or phototransistor that provides a change inconducted current depending on the amount of light detected. Photo detectors are mode sensitive

to certain wavelengths of light. Therefore, to improve sensing efficiency, the LED & photo

detector are often spectrally matched.

The lenses are used with LED & photo detectors to adjust the sensitivity or to increase the

sensing distance.

The output device of the sensor provides an interface signal to control logic. When the photodetector portion of the sensor sense enough change of light level it activates the output device.

For example an output device can be a relay.

Since the sensor consists of electronic parts, it is not sensitive to vibration & can handle a wide

temperature range. Typically the LED doesnt need replacement; therefore the sensor might be


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totally encapsulated, making them more rugged & reliable. A self-contained sensor contains:

Optics, Modulator, Amplification, Demodulator, and Output switch.

Fiber Optic Sensor

The fiber optics sensors are the smallest photoelectric sensors and can be used when the space

available for installation is too small. The fiber optic sensor is made of small transparent strandsfibers of glass or plastic, that conduct and guides light energy into and out of a specific

inspection area of interest. The bundles of fibers are usually within and protected by a flexiblesteel armored sheath.

The glass fiber type is able to withstand hostile sensing environments. The plastic fiber opticassemblies are made up of either one or two acrylic monofilaments in a flexible sheath. The

fiber optic assembly is manufactured in 2 styles:

- Individual fiber - one for emitter; one for receiver- Bifurcated - combines emitter & receiver in one

The most common problem encountered is the breakage of individual strands due to sharpening

or bending. (i.e. reciprocating machine).

The infrared sensors are specified in three sensing modes:

1) Diffuse sensing modeIn this mode the sensor has the emitter and receiver in the same package. The object is

detected when some part of the light generated by the emitter strikes the surface of the

object at some arbitrary angle and is diffused from the surface at all angles. The object isdetected when the receiver captures some small percentage of the diffused light that

returns to the sensor. In another word the objects reflects the light back to the sensor.

Design Tip:

In diffuse sensing mode the more light the object reflects (i.e. white) the better theobject is detected. The dark absorbing light (i.e. black) can have problems being

detected.

There is a special case of diffuse sensing called convergent. The convergent sensing

mode has range of distance with a center focal point that can detect and object. Inanother words, the object is detected if it is within the detection area, not closer not

farther.

2) Retro-reflective modeAlso called retro mode. Similar to the diffuse sensing this mode contains the emitter

and receiver, but uses a reflector to create a continue beam of light. The emitter produces

the light, toward the reflector target in another strategic location. The light rebounds onthe reflector, back to the sensor, where the receiver detects it. Retro is the popular for

conveyor applications where the objects are large (i.e. boxes, cartons, etc.) and the

scanning ranges are typically few feet.


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Design Tip:In retro-reflective mode, the object is detected when it cross and interrupts the beam

of light. Therefore the less light the object reflects, the better is detected. If theobject is a good reflector, when it cross the beam will reflect the light back to the

receiver, and be confused as the reflector, crossing undetected.

3) Opposed sensing

In this mode the emitter and receiver are separate and installed facing each other. Theemitter produces a ray of light, toward the receiver that is located strategically. The

object is detected when it travel and cross between the emitter and receiver interrupting

the ray of light. The oppose mode is the most precise and reliable method to detect an

object. Since the emitter and receiver are separate they can be optimized to have thereceiver and receiver far apart.

Design Tip:In opposed sensing the ray of light could go across a glass and cause the glass object

to go undetected. This problem might be resolved by moving the sensor installation

diagonally with the glass object.

2.2 Proximity Sensors

a. Capacitive proximity sensor

The capacitive proximity sensors are triggered by a change in the surrounding dielectric. Thetransducer of a capacitive sensor is configured to act as the plate of a capacitor. The

dielectric property of any object present in the sensing field increases the capacitance of the

transducer circuit and, in turn, changes the frequency of an oscillator circuit. A detectorsenses this change in frequency, and signals the output to change state.

b. Inductive proximity sensor

This sensor has an oscillator and a coil which radiate an electromagnetic field that induceseddy currents on the surface of metallic objects approaching the sensor face. The eddy

currents dampen the oscillator energy loss, it sensed as a voltage drop, which causes a change

in the sensors output state.

2.3 Sensor Interfacing

Normally the sensor is a digital device, but there are analog sensors that provide an output that is

proportional, or inversely proportional to the quantity of light seen by the receiver. Some sensors

have the option to be configured to work with positive or negative logic. In positive logic the

output of the sensor is either ON (detected target) OFF (no target detected). The opposed happenin negative.

The response time, or response speed, of the sensor is the time required for the output of a sensor

or sensing system to respond to a change of the input signal (e.g. a sensing event).


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Design Tip:The response time of a sensor becomes extremely important when detecting small

objects moving at high speed. Narrow gaps between adjacent objects also must be

considered when verifying that sensor response is fast enough for an application.

There are many types of outputs available, each with benefits & weaknesses.

1. Electromechanical Relay

The relay offers a reliable, positive means of switching electrical energy with a range ofcurrent contact rating.

Major advantages:

a. High switching current (various amps) relative to the electronic counterpart.b. Electrical isolation from sensor power source. Due to the isolation, (absence of

leakage current), they can be connected in series or parallel.

d. Different contact arrangements; SPST, SPDT, DPDT.

Disadvantages:a. Have a finite life span, (measured in millions of operations).

b. Inductive load can shorten the life span.c. Response times are much slower than must solid-state outputs. (Typically 15-25ms)

2. FET(Field effect transistor)The FET provides a fast switching of AC or DC power.

Major advantages:

a. Has very low leakage current.b. Can be connected in parallel like relays.

Disadvantages:a. Switching current capacity is limited (~30ma).

3. Power MOSFET( Metal Oxide Semiconductor Field Effect Transistor)

The MOSFET provides fast response time like a FET but with higher switching currentcapacity (300ma) and has very low leakage current

4. TRIACThe TRIAC is a solid-state output device designed for AC switching only.

Advantages:a. Offer high switching current; suitable to connect large contactors & solenoids.

Disadvantages:

a. Exhibit much higher leakage than FET & power MOSFETS (can exceed 1ma) thereforecannot be used with PLC & other solid state devices.

b. Cycle activation is required, meaning minimum response time of 8.3ms.


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5. NPN/PNP transistors

The transistor exhibits very low leakage current (measured in NA) and has a relatively low

switching current (typically 100ma) for easy interface to most DC loads. Response times of

sensors with transistor output can vary from 2ms to as fast as 30us.

2.4 Sinking VS. Sourcing

The sinking and sourcing concept applies to sensors with DC current only.

Current sinking outputThe current sinking output usually uses NPN transistors with its emitter tied the common(negative) side of the supply voltage. The concept of sinking means the current direction is

toward the sensor (the sensor receives current). The load must be connected between +

power connection and the sensor output. When the sensor detects an object provides the DC

common voltageto the load.

Current sourcing outputThe current sourcing output usually an open collector PNP transistor with its emitter tied to

the positive side of the supply voltage. The concept of sourcing means the current directionis away the sensor (the sensor send current). The load must be connected between the sensor

output and the DC common power connection. When the sensor detects an object provides

the + DC voltage to the load.

Standard wiring for DC sensors

Brown

BlackSourcing wire

WhiteSinking wire

Blue

Sinking LoadSensorInternal

Electronics Sourcing Load

DC neutral

Symbolic schematic

for a DC Sensor

DC neutral

Vcc

Vcc


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3.0 PLC Hardware description

The Programmable Logic Controllers (PLC) is an industrial computer constructed and adapted to

resist the industrial environment. The PLC has the following advantages:

Optical Isolation; this is the capability to receive input or send output information from/todevices without direct electrical connection between the device and the CPU. The electrical

signal is converted to a light signal; therefore the CPU is protected from the outside world.

Ability to change modules quickly for easy and rapid maintenance and repair.

User-friendly programming.

Adapted for industrial environment

The PLC is composed of the following:

a. A Central processing Unit (CPU)

- Contains one or more microprocessors

- Readonly memory (ROM), for the operating system- Random Access Memory (RAM), for user applications and requires battery back up.

- Electrically Erasable Programmable Read-Only Memory (EEPROM), do not requires

battery back up.

b. Input interface:Receive signals from the real physical sensors and convert the signals to logic levels

required by the CPU. The inputs can be discrete AC/DC signals or analog signals.Typical input devices are: Switches, sensors, pushbuttons, relay contact, and analog

transducers.

c. Output interface:

Connects and control real physical devices. They can be discrete AC/DC voltages or

analog signals. Typical output devices are: motor starters, valves, lights, and relay coils.

d. Power Supply:

Provides all the power required by the CPU, input and output interface modules. Varioustypes of power supplies are available to meet power requirements.

e. Rack:

The rack is the chassis that holds the components mentioned above and contains the

electronics to interconnect them.

There are various PLC manufacturers such as: Allen-Bradley, Siemens, Omron, General Elecric,

Modicon, IDEC, to mention a few.

CHAPTER 3PLC Hardware


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A very common PLC processors used are the Allen-Bradley SLC 500 family. This family hastwo type of PLC, fixed and modular.

The fixed processors combine the CPU, Input, outputs and power supply in one chassis unit.

The modular processor includes all the components previously mentioned (CPU, Inputs,Outputs, power supply) separate units. Therefore a mounting rack is used to accommodate

all the components, to provide the electrical power and communication signals connections

between the power supply, processor and the I/O modules. Example of the SLC-500 familyof processors are:

- SLC 5/01- SLC 5/02 (DH-485 communication capability)

- SLC 5/03 (DH-485 and RS-232 communication capability)

- SLC 5/04 (DH+ and RS-232 communication capability)

- SLC 5/05 (Ethernet and RS-232 communication capability)

Rack and slot number

The modular SLC-500 requires as a minimum one rack and can handle up to three racks. The

racks come in various sizes; 4, 7, 10 and 13 slots. The slots are space inside the rack where the

processor and I/O modules are inserted. The main rack contains the processor. If more than one

rack is used for the application, the extra racks are called expansion racks. The processor alwaysis on the slot 0 of the main rack. The other expansion racks do not require a processor, only a

remote adapter module wired (in Daisy chain) to the main rack.

Something to remember is that although you can use up to three racks, the combination of the

racks can provide only a maximum configuration of 31 slots (0 to 30) slots.

Example of rack configurationRequirement: A modular SLC-500 will be used for an application that requires 22 slots. Specify

a possible rack configuration for this system.

Solution:With this requirement three racks of 4 will provide only 12 slots ( 3 racks x 4 slots = 12 slots),

and three racks of 7 slots will provide only 21 slots. Therefore those configurations are

discarded. One solution is to use three racks of 10 slots that will provide a total of 30 slots.Various other solutions for the rack configuration can be generated. For illustration purposes the

following configuration is also valid; main rack of 7 slots, two expansion racks of 4 and 13 slots.

LOT 0 1 2 3 4 5 6 SLOT 7 8 9 10 SLOT 11 12 13 14 15 16 17 18 19 20 21 22 23

Remote I/O Network


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As we can see, the racks can be combined to meet the desired requirements. In this case weprovide 24 slots, which are 2 slots more than what is requires. Those two spare slots will be

available for future applications.

Design Tip:

1. Special consideration must be place to the space needed to mount the racks. The rackrequires to be separated from other components around. This is important to have

enough space for the air to flow through the rack to remove hot spots. Refer to the

PLC manufacturing installation guide for more information.

2. In many cases, the space available for control equipment is limited; therefore the

selection of the rack size could be important. The bigger the PLC rack the bigger the

space required, especially if the PLC is mounted inside an enclosure.

3.1 Networks available on the SLC 500 family of PLC.

1. Remote I/OIs used to connect all the PLCs to the remote I/O racks. The data transfer is 230.4 kbps for

cables up to 2,500 ft, or 57.6 kbps for cables up to 10,000 ft.

2. DH-485

This network is used to transfer information between other PLCs, operator interfaces and/or

other PC computer. The maximum number of nodes allows is 32 nodes. The data transfer

depends of the length of the network, for example for up to 4,000 ft is 19.2 kbps.

3. DH+This network is similar to DH-485, but faster. For example 57.6 kbps for up to 10,000 ft, andcan handle a maximum of 64 nodes.

4. Ethernet

Is used to transfer information between the PLCs and computers, for example to connect theplant computer network. It can handle data transfer rates up to 10,000 kbps, over unlimited

number of nodes, and supports TCP/IP protocol.

5. DeviceNet

Is one of the latest networks being used. It allows to connect control devices (i.e. sensors)

directly to the PLC without the need to hardwire it to an I/O rack. The maximum length is1,600 ft with data transfer rate up to 125 kbps. It can handle a maximum of 64 nodes.


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3.2 Hardware Design Considerations

Power supply consideration

The rack power supply provides the power to the rack for the operation of the processor and

Input/Output modules. Therefore select the correct size of the power supply with enough currentto handle the PLC rack system. This power supply also provides DC power for external sensors

that might required this type of power. In some occasions the amount of DC power required forall the sensors exceed the amount of DC power available on the rack power supply. In that case

a dedicated external DC power supply is used instead of the DC connection available on the rack

power supply.

Wiring

Appropriate sizing of wires shall be made according to the National Electric Code (NEC). All

the wires should be identified with a unique number at each end of the wire. This number shallmatch the electrical drawings. The wire color code recommended for is as follow:

Application Wire color

- DC voltage Blue

- AC voltage Red, Black- AC common White

- AC neutral Green

- Remote power (not controlled from the local breaker) yellow

In some occasions a multi-conductor cable (with various colors) are used. This type of wire has

the advantage of providing an easy way to identify the wire by color and also comes in a cablethat is easy to manage during routing.

The transients are very short duration of voltage (or current) pulses that can be many times larger

in magnitude than the supply voltage. Transients are usually caused by the operation of a heavyload or of any size inductive load like motors, contactors, and solenoids. Voltage transients can

cause false actuation of fast electronic circuits such as solid-state counters, one-shot timers, and

latching outputs.

Design Tip:1. The problems resulting from transients are dealt with by careful shielding and

grounding of remote sensor lead wires, by physical separation of signal wires frompower wires in wire ways, and by installing transient suppressors directly across

offending loads.


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Wire routing

Put special attention to the wiring routing, do your best to reduce at maximum the mixture of DCwires and A/C wires in the same wire duct. The DC analog signals should be segregated from

AC wires as much as possible.

Design Tip:

A common technique used is to have the DC wires running vertically in the right side of therack and the AC wires running vertically on the left side of the rack.

PLC RACK

With Input/Output modules

DCWIREDUCT

WIRE DUCT

Power Distribution Area

ACWIREDUCT

WIRE DUCT

Terminal Blocks

Area

Example Enclosure layout for PLC

Enclosure

Mounting Panel


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4.0 Memory Map of PLC processor

Allen-Bradley divides the PLC memory in files. There are two types of files: Program files anddata files. Either one program or data file can be divided on a maximum of 256 files (0-255).

4.1 Scan Time

Is the time required by the PLC to update the inputs, execute the ladder program and update the

outputs. The ladder program execution is performed rung by rung, from left to right.

Time to update

Input image

Time to update

Output image

PLC Scan time

Overhead

Program execution time

The Scan time is composed of the following:

1. Time to update the Input Image with physical Inputs.2. Time to execute the program (longest time).

3. Time to update the output image and physical outputs.

4. Processor overhead time (shortest time).

Digital Inputs

Analog Inputs

I/O image files

Other data files

Digital Outputs

Analog Outputs

Ladder programs

Data files

Program files

PLC Memory

Physical devices Physical devices

Relationship between I/O modules, Data Storage, and ladder program

CHAPTER 4PLC Memory Map


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The Program file memory area is divided as follows:

Program

File no.

Description of program files

0 System configuration information, password, processor name1 Reserved

2 Contains the main ladder program

3 to 255 User subroutines called by the main program

Data files

The data file section contains status information related to the I/O and the instructions used onthe main program and subroutines. The data files are divided in types of information as follows:

Data File

number

Data File

Name

Starting

Address

Range of values Data Stored

Or Use for0 Output Image O: Depends of rack

configuration

State of physical outputs

1 Input Image I: Depends of rackconfiguration

State of physical inputs

2 ProcessorStatus

S2: 0-82 Status info. of processor

3 Binary B3: 0-255 words equalto 4096 bits

User program internaluse

4 Timers T4: 0-255 timers Timer accumulator,preset, and status

5 Counters C5: 0-255 Counter accumulator,

preset, and status

6 Control R6: 0-255 words Instruction specific;

Length, position, status

7 Integer N7: 0-255 words Positive or negative

whole numbers

8 Floating Point F8: 0-255 words Positive or negative

number with decimals

9 ASCII A9: 0-255 Alphanumeric

characters10-255 Optional As

required

0-255 Configurable as

required by user


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4.1 Addressing Format

The following format must be used to refer (address) to a specific area of the data memory.

Example: Addressing word 2 Example: Addressing Input 0of integer data file 7 located on slot 2

FN : E . W / B

File type

File number

Element delimiterWord number

Word delimiterElement number

Bit delimiter

Bit number

N7 : 2

Integer file

File number

Element delimiter

Element number

I : 2 / 0

Input file

Element delimiter

Element number

(Slot 2)

Bit delimiter

Bit number


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Example: Addressing bit 22 Example: Addressing accumulated value of timer 7of binary file 3 of file 4

(same as B3:1/6)

In the previous example, B3/22, we start counting at B3:0/0 and keep counting in the next word

until we reach to bit 22 which is B3:1/6. Also we can specify bit 27 start counting in word one(1) by specifying B3:1/27= B3:2/11

Word

B3:0 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

B3:1 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

B3:2 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Symbols

A description (tag) can be assigned to an address, this is known as symbol. The symbol is a

name or tag assigned to an address that the user could refer to instead of using the address. Thishas the advantage of having direct reference to the device being controlled instead of learning the

address. To assign a symbol to an address using RS-Logix 500:

1. Enter in the program the instruction with address.

2. Place the mouse over the desired instruction and right click the mouse. Select Edit Symbol

and enter the description for the address.

B 3 / 22

Binary file

File number

Bit delimiter

Bit number

T 4 : 7 . ACC

Timer File

File number

Element delimiter

Element number

(Timer 7)

Word delimiter

Word Mnemonic

(Accumulator)

B3:1/6= B3/22

BIT

B3:1/27= B3:2/11


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5.0 Basic Instructions

The set of instructions depends on the PLC model. Some models have extra instructions not found

in smaller PLC. Refer to each PLC documentation to understand which instructions are available.In the appendix a list of instructions is included for reference.

Concept of Input and output instructions

The instructions are divided in two main types, input instructions and output instructions. The inputinstructions cannot be positioned in the last right position of the rung. Only output instructions can

be the last instruction to the right. Now, you can have various output instructions in parallel located

in the right side.

The instructions with similar functions are grouped together to facilitate their finding. These groups

of instructions are: Bit, Timer/Counter, Input/Output, Compare, Compute/Math, Move/Logical,

File/Misc., File Shift/Sequencer, Program control, ASCII control, ASCII string, Micro high speedcounter, Trigonometric functions and Advanced math.

5.1 Bit Instructions

The first three instructions, XIC, XIO, OTE are similar to the relay logic. Therefore think in term of

relay logic when learn them.

5.1.1 Examine if closed (XIC)

Also called Normally Open. Similar to relay logic, this instruction looks for an ON state. You

can think that this instruction is like a relay contact, in which it closes when its relay coil isactivated with logic one (1). In another words, when the reference address is true (1), the

instruction also will be true.

If the reference address is a physical input, it will close (change state) when the field device appliespower to the input. If the address is an internal bit (for example a bit from the B3 file) then it will

close when that address has a one (1).

5.1.2 Examine if Open (XIO)

Also called Normally Closed. Similar to relay logic, this instruction looks for an OFF state. Youcan think that this instruction is like a relay contact, in which it opens when its relay coil is activated

with a logic one (1). This is negative logic, in another words, when the reference address is true (1),

the instruction will be false.

If the reference address is a physical input, the instruction XIO will open (change state) when the

field device applies power to the input. If the reference address is an internal bit (for example a bit

from the B3 file) then the instruction XIO will open (is false) when that address has a one (1).

CHAPTER 5Basic SLC Instructions


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5.1.3 Output Energize (OTE)

This instruction controls the status of a bit in memory. Since this is an output instruction, it goes on

the right side of the rung. The instruction is true (1) if the conditions preceding are true.

Possible applications

If the address corresponds to a physical output, the device wired to the output will be energized

when the instruction is true. If the reference address is an internal bit (for example a B3 file), thenthe corresponding bit instructions (XIC or XIO) will be true when the instruction is true.

5.1.4 Output Latch (OTL)

This is a retentive output instruction that keeps the last state. Meaning that if the preceding

conditions are not true the instructions or if the processor lost power, the instruction maintains its

last logical state condition (0 or 1). When the preceding conditions are true, the instruction is trueand sets the reference bit equal to one (1). The bit remains set to 1 even if the preceding

conditions are false. The OTU instructions can be used to set the reference bit to 0

Possible Applications

This instruction can be used to identify when an event occurs. For example if a condition or series

of conditions only are activated during a short period of time, this instruction will be activated andstay ON even when the conditions are not present any more.

Most of the time, this instruction is used in pairs with the OTU (unlatch) instruction, with bothinstructions referencing the same address. But the bit can be unlatched (set to 0) with other

instructions as well.

5.1.5 Output Un-Latch (OTU)

This is a retentive output instruction that keeps the last state. When the preceding instructions aretrue, the instruction is true and sets the reference bit equal to 0. The bit remains 0 even if the

preceding conditions are false. To set the reference bit back to 1 the OTL instruction could be

used.

Most of the time, this instruction is used in pairs with the OTL (latch) instruction, with both

instructions referencing the same address. But this is not mandatory, since the bit can be set to 1by other means in the logic.

L

U


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5.1.6 One shot rising (OSR)

This instruction is a conditional input that allows the logic to its left to be executed only for one

scan of the logic (until the instruction is executed again).

The address bit assigned to the OSR instruction allows it to remember its previous rung state. Is setto 1 if the proceedings conditions to the OSR are true, the bit is reset to 0 when the conditions

are false. The bit address assigned must be unique, therefore dont use it elsewhere in the program.

Use a bit from the binary or integer file.

5.1.7 Scan Time

Refer to Section 4.1

5.2 Timer and counters instructions

These instructions are considered programs output instructions, therefore must be the lastinstruction on the right side of the rung. These instructions will be energized when the preceding

instructions on the rung are true.

Timers

The timer consumes three words per instruction:

- Word #1 is for the instruction control bits (the control word)- Word #2 is to save the preset value.

- Word #3 is to save the accumulator value.

Bit number15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Word #1 EN TT DN

Word #2 Preset Value

Word #3 Accumulated Value

For SLC 5/01 the time-base is 0.01For SLC 5/02 , 5/03 , 5/04 the time-base options are : 1.0 and 0.01 seconds.

The timing accuracy is0.01 to 0 seconds with a program scan of up to 2.5 seconds.

OSR


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5.2.1 Timer On-delay (TON)

When this instruction is energized it accumulator value increments. Its accumulated value is resetto zero when the rung conditions are loss.

Description of the Control Bits

Bit 15 = Enable bit (/EN); This bit is set to 1 when the rung condition are true, means that the

instruction is energized.

Bit 14 = Timer timing bit (/TT); This bit is set to 1 only when the timer is incrementing. When

the accumulator reaches the Preset value, the bit is set to 0.

Bit 13 = Done Bit (/DN); This bit is set when the accumulator is equal or greater than the Presetvalue. Under normal condition the timer will increment only up to the preset value and

stop. If the instruction is enable (energized), the programmer could create logic to

move to the accumulator a value greater than the preset value. In that case, the done bit

and the enable bit will stay set to 1.

5.2.2 Timer Off-Delay (TOF)

This timer contrary to the TON instruction, will increment only when the rung conditions are not

true, in another words when the TOF instruction is not energized. The instruction is reset when therung conditions are true (the TOF instruction is energized), the reset will cause the following:

/En=1, /DN=1, /TT=0 and accumulator =0.

Description of the Control Bits

Bit 15 = Enable bit (/EN); This bit is set to 1 when the rung condition are true, means that theinstruction is energized.

Bit 14 = Timer timing bit (/TT); This bit is set to 1 only when the timer is incrementing. When

the accumulator reaches the Preset value, thebit is set to 0.

Bit 13 = Done Bit (/DN); This bit works oppose as in the TON instruction. This bit is set to 1

when the instruction is energized or while is incrementing. The bit is set to 0 when the

Timer On Delay

TimerTimer Base

Preset

Accum

T4:1

1.0

10

0

( EN )

( DN )

TON

Timer OFF Dela

Timer

Timer Base

Preset

Accum

T4:1

1.0

10

0

( EN )

( DN )

TOF


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accumulator is equal or greater than the preset value. Under normal condition the timer

will increment only up to the preset value and stop. If the instruction is not energized,

the programmer could create a logic to move to the accumulator a value greater than thepreset value. In that case, the done bit and the enable bit will stay set to 0.

Is important to mention, that for proper function of the TOF instruction, is better to control its reset

using the rung conditions instead of the RES instruction (refer to RES instruction). In anotherwords, it shall be reset energizing the instruction by activating its rung conditions. The reset

instruction could cause improper operation.

5.2.3 Retentive Timer On-Delay (RTO)

The RTO instruction starts to increment when the rung conditions are true (when the instruction isenergize). But it retains the accumulated value when the rung conditions are false. When the

instruction is energize again, the accumulated value starts from the last value used. This feature

makes the RTO instruction excellent to add time at different periods. For example, to calculate the

total time a machine has being ON for a period of time.

The status bits definition are identical to the TON instruction. It is important to mention that the

timer timing bit (/TT) stays set as 1 while the instruction is in the process to reach the preset

value, even though the RTO is not energize.

Timer addressing examples:

T4:1/15 = T4:1/EN

T4:1/14 = T4:1/TT

T4:1/13 = T4:1/DNT4:1.1 = T4:1.PRE

T4:1.1/0 = Bit 0 of preset value

T4:1.2 = T4:1.ACCT4:1.2/0 = Bit 0 of accumulated value

Retentive Timer On

Timer

Timer Base

Preset

Accum

T4:2

0.01

100

0

( EN )

( DN )

RTO


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Counters instructions

The counter instructions are mostly used to count events. These instructions are consideredprograms output instructions, therefore must be the last instruction on the right side of the rung.

These instructions will be energized when the preceding instructions on the rung are true.

Same as the timers, the counters consume three words per instruction:- One word for the instruction status bits (the control word)

- One word for the preset

- One word for the accumulator.Bit number

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Word #1 CU CD DN OV UN

Word #2 Preset Value

Word #3 Accumulated Value

5.2.4 Counter Up (CTU)

Data required for the CTU instruction

- Counter number = Is also known as the counter address. Enter C5:#, where # is the counter

number within a range of 0 to 255.

- Preset value = This is the number of events desired to detect. Is a fix number and is used tocompare with the accumulated value.

- Accumulated value = This is the number of events detected. The accumulated value increments

by one when the rung conditions change from false to true. In the example shown below, when

the condition X change state from 0 to 1 the accumulated value of C5:1 increment by one (from

0 to 1). The accumulated value will maintain its valued, even when the condition X=1, it willincrement again in the next transition of X from 0 to 1. When the accumulated value is equal or

greater than the preset the done bit is set to 1.

The status bit used for the CTU instruction are as follow:

Bit 15 (CU) = Counter UP. This bit is set to 1 when the instruction is true (is energized).Bit 14 (CD) = Counter Down. Not applicable for the CTU instruction.

Bit 13 (DN) = Done bit. Is set to 1 when the Accumulator is equal or greater than the Preset.

Bit 12 (OV) = Overflow bit. Is set to 1 when the Accumulator wraps from +32,767 to 32,768.Bit 11 (UN) = Underflow bit. Not applicable for the CTU instruction.

Count Up

Counter

Preset

Accum

C5:1

10

0

( CU )

( DN )

CTUx


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5.2.5 Counter Down (CTD)

Data required for the CTD instruction

- Counter number= Is also known as the counter address. Enter C5:#, where # is the counter

number within a range of 0 to 255.

- Preset value = This is the number of events desired to detect. Is a fix number and is used to

compare with the accumulated value.

- Accumulated value= This is the number of events detected. The accumulated value decrements

by one when the rung conditions change from false to true. In the example shown below, when

the condition Y changes state from 0 to 1 the accumulated value of C5:2 decrement by one(from 5 to 4). While the condition Y=1 the accumulated value stays the same, it will decrement

again in the next transition from 0 to 1. When the accumulated value is equal or greater than the

preset the done bit is set to 1.

The status bit used for the CTD instruction are as follow:

Bit 15 (CU) = Counter UP. Not applicable for the CTD instructionBit 14 (CD) = Counter Down. This bit is set to 1 when the instruction is true (is energized).

Bit 13 (DN) = Done bit. Is set to 1 when the Accumulator is equal or greater than the Preset.Bit 12 (OV) = Overflow bit. Not applicable for the CTD instruction

Bit 11 (UN) = Underflow bit. Is set to 1 when the Accumulator wraps from -32,768 to +32,767.

Comments and applications for CTU and CTD instruction

1. The status word includes all the bits required by both instructions; therefore the programmer

must use and interpret the applicable bits for the instruction being used.2. The relationship of the overflow and underflow bit is as follow:

+32,767

0

-32,768

Count Down

Counter

Preset

Accum

C5:1

10

0

( CD )

( DN )

CTDY

CTDCTU Underflow conditionOverflow condition


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3. Done bit

In the CTU and CTD instructions the done bit always is going to be set to one, when the

accumulator is equal of greater than the preset. Therefore in the case when the preset isnegative, a value of zero in the accumulator will activate the done bit. The reason is, because

the value of zero in the accumulator is greater than any negative number in the preset.

4. Incrementing and decrementing a value.If the same address is assigned to the CTU and CTD instruction, the result is a logic that allows

to increment and decrement the same accumulator.

Example problem:

Design a PLC based control system to turn ON a red light when the capacity of people inside aroom reaches a maximum of 50 people.

Solution:

Lets wire a red light in output O:2/0. We need a sensor at the entrance of the room to count the

people entering the room, wired to input I:1/1. Also we need a separate sensor at the exit to

detect the people leaving the room, wired to input I:1/2. For purpose to synchronize the counter,lets add a key switch to reset the counter at the beginning when the room is empty. The logic

will be as follows:

Count Up

Counter

Preset

Accum

C5:1

50

0

( CU )

( DN )

CTUI:1/1

Count Down

Counter

Preset

Accum

C5:1

50

0

( CD )

( DN )

CTDI:1/2

I:1/3( RES )

C5:1

O:2/0C5:1/DN

( END )

0

1

2

3

When the entrance sensor is activated, itincrements the accumulated value of

counter C5:1

When the exit sensor is activated, it

decrements the accumulated value of

counter C5:1

When the accumulator is equal to the

preset, the done bit is activated, turning thered light in O:2/0

When the room is empty, the accumulator

must be zero. If not the key switch in I:1/3

can be activated to reset the accumulator to

zero.

Count Down

Counter

Preset

Accum

C5:1

-10

0

( CD )

( DN )

CTDI:1/0


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5.2.6 Reset (RES)

The RES instruction is used to reset timers and counters. The address assigned to the RESinstruction must be the same address of the timer or counter desired to be reset. For example if we

want to reset the counter C5:1, then your RES instruction address must be C5:1.

When the RES is energized the accumulated value and control bits of the timer or counter are reset.

Hints:Resetting a counter: When the RES instruction is energized, it resets the counter control bits, whichincludes CU or CD and also resets the accumulated value to cero. When the program

continues, if the corresponding counter that was reset still energized, it will increment to one in thecase of CTU or decrement to minus one (-1) in the case of the CTD. This would cause a doublecounting of an event used to trigger the counter.

Possible Solution:

Use an OSR (One Shot) instruction before the counter instruction to make sure the counter only

counts real changes of the event.

If the counter preset value is negative, the RES instruction will reset the accumulated value to zero.

That causes the done bit to be set to 1 in both the CTU or CTD instructions.

Warning! The use of RES instruction to reset a TOF instruction might cause problems. The RES

always clears the status bits and the accumulated value, causing to disable the TOF instruction untila change of state on the rung input conditions occur. This could result in unpredictable machine

operation or injury to personnel.

Now a possible logic to correct this problem is the following:

This logic will allow to reset the timer any moment when the timer is incrementing, and the timer

will start to increment from zero again.

C5:1

( RES )( RES )

T4:1

( RES )

T4:1

T4:1/DN

B3:0/0

Timer OFF Delay

Timer

Timer Base

Preset

Accum

T4:1

1.0

10

0

( EN )

( DN )

TOF


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Automation Engineering Examples


Practice problems for first test.

1. Use the information in the appendix to get familiar with the RS-Logic 500 program:a. Learn to create a new project.

b. Navigate thru the data and program files.

2. Using the instructions XIC, XIO and OTE:a. Write a PLC program to simulate a logic AND, OR, EXOR.

b. Learn to use the RS-Emulator

3. Using the instructions XIC, XIO and OTE:

a. Write a PLC program to control a DC motor. Use a NO Start PB and a NC Stop PB. Showthe status of the motor (ON and OFF) with lights.

4. Repeat the previous problem using the instructions OTL and OUT.

5. Use a TON instruction to control a light, to flash alternating ON and OFF. A two position

selector switch is used to controls two possible delay options.

6. Control two lights flashing alternating, only one ON at a time. A two position selector switch isused to control the two possible delay options. When the START pushbutton is pressed the

sequence must be executed automatically three times.

7. Turn ON 3 lights, with 3 different ON time delays. A selector switch is used to decide the delay

to be used. Details to be provided by class instructor.

8. Control an assembly machine to produce a six pack. Details to be provided by class instructor.

9. Control 3 motors that turn ON in sequence when a pushbutton is activated. Once the motor turnON, stays ON while the others turn ON. At the end all three motors are ON.

10. Control a motor with the following functions: ON, STOP, FORWARD, REVERSE and JOG.

Assume that two coils are used to control the direction of the motor, one output for forward andone for reverse. Make sure the two outputs never are ON at the same time.

11. Control a toaster (tostadora de pan) with 3 heat setting positions.

a. In low turn ON the output 1 for 20 secondsb. In Med, turn ON the output 1 and 2 for 15 seconds

c. In Hi, turn ON ouputs 1 and 2 for 25 seconds

Inputs:- 3 heat positions (Low, Med, Hi)- Bread slot is down (limit switch),

an mechanical lock is used to

hold the slot down.Ouputs:

- 2 outputs to control the heaters

- One output to release and raise the slot of the bread.

HI MED LOW

R3 R2 R1


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Chapter 6Program Control

6.1 Program Control Instructions

6.1.2 Jump (JMP) to Label (LBL)

You can have more than one JMP instruction addressing the same label (LBL). The program scantime is reduced when jumping forward to a label, because is omitting program rungs. Jumping

backward lets the controller execute program segments repeatedly.

Note: Be careful when using the JMP instruction to move backwards or loop through yourprogram. To loop too many times, may cause the watchdog timer to time out, resulting a processor

fault. You could use a counter, timer, or the program scan register (S:3, bits 0-7) to limit the amount

of time you spend looping inside of JMP/LBL instructions.

You can enter a decimal label number in the range of 0-999. But you can use up to 256 labels for

SLC controllers in each subroutine file (not to exceed 256 labels in entire project). And up to 1,000

labels for MicroLogix controllers in each subroutine file (not to exceed 1,000 labels in entireproject).

6.1.3 Troubleshooting tools

Temporary end (TND)

This instruction is used to disable a specific part of the ladder logic. All the logic after the

TND will not be executed by the PLC.

X

( END )

8

9

When the rung condition X the processor

umps forward or backward to the corresponding

label with the same address specified in the JMP

instruction. The program resumes execution at

the rung where the LBL is found (in this case

Rung 20).

While the JMP is executed, the instructions after

the JMP and before the LBL are not executed. In

this example, the timer T4:1 is not executed

while the JMP is active.

:

::

:

( JMP )

Q2:1

( LBL )

Q2:1B3:2/0

20

T4:1/DNTimer OFF Delay

Timer

Timer Base

Preset

Accum

T4:1

1.0

10

0

( EN )

( DN )

TOF

:

:

:

:

When the JMP in rung 8 is activated, it causes

the program scan to jump to this line where the

same address LBL is located.


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Master control reset (MCR)

Two MCR instructions, one at the beginning and one at the end of the area, are used to define a

group of rungs called a zone. The zone can be enabled or disabled to activate or deactivated

the function defined by the rungs within the zone. The zone is enabled when the conditions of

the first MCR that defines the zone is energized. When the first MCR is not energized, theladder logic within the zone is not executed, and all the non-retentive output instructions are de-

energized. That includes the reset of the timers. It is important to mention that the first MCR,

defining the beginning of the zone, must have a rung condition. If it doesnt have rungconditions the verification of the project will show an error. Meanwhile the last MCR of the

zone cannot have rung conditions.

Suspend (SUS)

This instruction is used to debug or diagnose your ladder program. When the rung conditions

are true, this instruction places the controller in the Suspend Idle mode. The suspend ID isplaced in word 7 (S:7) of the status file. The suspend file (program or subroutine numberidentifying where the executed SUS instruction resides) is placed in word 8 (S:8) of the status

file. All the outputs are de-energized.

( END )

7

9

11

T4:1/DNTimer ON Delay

Timer

Timer Base

Preset

Accum

T4:1

1.0

10

0

( EN )

( DN )

TON

X8 ( MCR)

B3:2/0B3:0/0

( MCR)

The zone is defined from rung 7 to rung 10.

When the rung condition X is energized the

zone is enabled and the TON instruction is

going to start. Notice that the first MCR in rung

8 has rung conditions and the second MCR does

not.

When the rung condition X is de-energized

the zone is disabled and the TON instruction

resets automatically.

10 Timer OFF DelayTimer

Timer BasePreset

Accum

T4:1

1.010

0

( EN )

( DN )

TOFB3:0/2

Attention:

The TOF instruction is activated (increments)

when the zone is disabled. Therefore properprecaution must be considered when is used

within a MCR zone.


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6.1.4 Subroutines

A subroutine is a program that contains a series of rungs (similar to the main program) in a separatefile number ranging from file number 3 to 255. Most of the time the subroutine contains a function

that perform a specific task. One of the advantages of using subroutines is that this function not

necessarily is used all the time, therefore is called from the main program (file no. 2) when is

necessary.

The following instructions are used to program subroutines:

- Jump to subroutine (JSR) , Subroutine label (SBR), Return from subroutine (RET)

X

( END )

0

:

:

:

:

Jump To Subroutine

SBR File Number U:3

JSR

( END )

0

1

:

:

:

:

( )

B3:0/0

20

T4:1/DN

Subroutine

SBR

LADDER No. 2

Timer On Delay

Timer

Timer Base

Preset

Accum

T4:1

1.0

10

0

( EN )

( DN )

TON

Return

RET

LADDER No. 3

When rung conditions X is true the JSR

instructions is executed, causing the execution to

continue in program file no.3 (subroutine). After

finishing scanning the file no. 3, the program

scan returns to the main file no. 2.The first instruction of the subroutine must be

SBR. Then the specific rungs for the subroutine

follow, and finally a RET instruction must be the

final instruction.


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6.1.5. Concept of Subroutines

You can nest subroutines, in other words, you can call a subroutine from the main program and thenfrom that subroutine on to another subroutine. Keep in mind the following rules when nesting

subroutines:

- For Fixed and 5/01 processors , you can nest subroutines up to 4 levels.- For 5/02, 5/03, 5/04, 5/05 and MicroLogix processors, you can nest subroutines up to 8 levels. If

you are using an STI subroutine, I/O event-driven interrupt subroutine, or user fault routine, you

can nest subroutines up to 3 levels from each subroutine. With MicroLogix 1000 processors youcan nest subroutines up to 3 levels from the HSC Interrupt subroutine.

- When you call a subroutine it always jump to the first rung of the subroutine. When you nest

subroutines they return back in the same reverse order they were called. A runtime error willoccur when calling more subroutines than allowed. Also cannot call a subroutine already active.

When the subroutine stops being scanned, all the values inside the subroutine are freeze and stay in

the last state and retain the last values. For an example, an OTE output will maintain its last state.

In the specific case of a timer, although the accumulator is frozen, the timer internally keeps

counting but not reflected for the purpose of logic; therefore this means that when the subroutine isactivated the timer is updated with the last time counted.

For example: In the case of two timers with preset 100, T4:1 inside a subroutine and T4:0 in the

main program. If both start at the same time, and the subroutine stops when the accumulator is 10,the T4:0 keep incrementing but T4:1 maintains the ACC=10. If the subroutine is activated 10

seconds later when the t4:0 accumulator =20, then t4:1 accumulator will become 20 also; like it was

counting.

Now, if the subroutine stops when t4:0 acc=50, and is activated back after when the t4:0 have beingreset and its acc=10, then the t4:1 acc will become 100, (like it is finish) and will be reset to cero

and start again causing t4:0 to be a difference about 11 seconds ahead.

Bottom line: If the timer is stopped and return before its preset time value was complete, it

continues like it never lost a time. But if it stop, and return after a time greater then its preset value,it will reset to zero.


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Chapter 7Data Management

All the instructions used to manage data works a word level. In another words, they use the sixteen

(16) bits of the word.

7.1 Move and Logical Instructions

Move (MOV)Is used to move a value or the content of an address to a specific address location of the PLC

data table. The destination value is overwritten.

Move with Mask (MVM)

This is similar to MOV, but with a mask we can specify which bits we can move. If all the 16bits are selected (set to 1), the instruction is identical to the MOV instruction.

And (AND)When the rung conditions are true, this output instruction executes an AND function between

the values in source A and source B and write the result in the destination specified.

Move

Source

Dest

B3:1

N7:0

MOV

0000000000001010

automation book v6

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