Introduction: Programmable logic controllers (PLC) have been evolved out from Relay logic circuits (RLC). A typical RLC circuit is as shown in Fig 1.1 L 1
PB1
R12
L1-L2 PB1 PB2 R1 R12
Control Voltage (AC/DC) Start Pushbutton Stop Pushbutton Relay Auxiliary relay
PB2
L 2
R1 Fig 1.1
R12
Circuit Functioning: When PB1 is pressed, R1 & R12 coils pickup. This makes R12 Normally open (NO) Contact to close. Once R12 contact closes even if PB1 is released, R12 will remain ON as there is an alternative path for the coil (Termed as Latching). The only way to break the latch is to press PB2.
As seen the logic circuits are hard wired. When the process became complicated and automation level increased so did the circuits. These RLC’s had many drawbacks. Viz., 1. Circuits were bulky: a. Apart from relays, external components like counters, timers etc. were to be used. b. Relays had limited number of auxiliary contacts. Hence if the circuits demanded for more contacts, then additional relays (Aux relays) were to be used in parallel to actual relays (e.g. R12 in Fig1.1). Hence more relays were required. 2. Troubleshooting was very difficult. a. If a particular relay was not becoming ON (e.g. R1 in Fig.1.1), the entire loop had to be traced from one point to other. A rather tedious process. 3. Inflexible: a. Logics were built on hardwired circuits. Hence any changes in the logic, the wiring had to be changed. In some cases it would be impossible, as the required contacts (Normally open (NO) / Normally closed (NC) would not be available. 4. If the logic were complicated, sometimes it would not be feasible to build a RLC. To overcome the above drawbacks, a new product called the PROGRAMMABLE LOGIC CONTROLLERS (PLC) Emerged.
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Programmable logic controller (PLC) is a solid-state device, basically designed to perform logical decision making for industrial control application. Since their development in early 1970’s, PLC’s have evolved to challenge not only relays but also other discrete control devices such as stepping switches, drum sequencers etc. The PLC’s is composed of electronic circuit with a microcomputer centered. However, it can be equivalently regarded as an integrated body of ordinary relay, timer, counter etc. The block diagram of a PLC is as shown in Fig 1.2: NO CONTACT PUSHBUTTO NC N CONTACT PUSHBUTTO N NC CONTACT SWITCH
I N P U T S
PLC POWER SUPPLY
PROCESSOR
O U T P U T S
RELAY COIL LAMP SOLENOID COIL
Fig 1.2
Power Supply: It is basically required for the circuits of the PLC to function. These power supplies are designed and rated only to operate the internal structure and not the field elements. The external supply to the PLC can be AC/DC and can be of different ranges, but the PLC power supply converts these to the appropriate voltages required for internal functioning of the PLC circuits. The common voltages are: AC: 110v, 220v DC: +24v, 110v Processor: This is the heart of the PLC. It interfaces the input and output subsystems through software written to it. The input and output subsystems are explained in the preceding discussions.
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INPUT SUB SYSTEM: The sensing elements (input elements) are wired to the input section of the PLC. These elements sense the dynamic status of the machine operation or process. Inputs are classified into two: 1. Digital 2. Analog 1. Digital inputs: These inputs have only two states, viz., ON or OFF (digitally 1 or 0). Therefore these are also called as discrete inputs. Elements used to give the various commands for e.g. Push buttons, Limit switches, Selector switches, Proximity switches, Level switches and Pressure switches etc. are directly connected to the input of the PLC. 2 . Analog inputs: These inputs have multiple states and rather continuously changing one and are having a range of values. Electrically these are categorized into two: i)
ii)
Voltage : The commonly used ranges are 1. 0 to 10 Vdc -unipolar 2. –10 to +10 Vdc -bipolar 3. 0 to 5Vdc Current : The commonly used ranges are 1. 0 to 20mA 2. 4 to 20mA
The field parameters like pressure, flow, temperature etc are converted to electrical parameters through transducers and are converted further to the above voltage / current signals through transmitters. The output of transmitters is then connected to analog inputs of the PLC. The PLC in turn converts these voltage / current signals to their equivalent digital values through the analog to digital convertors. Typical example is shown below
Process
Pressure to resistance Transduce r
Resistance to 4-20 mA
Transmitte r
Range: 0 to 10 kg/cm2
Analog Input of PLC 4-20 mA to 4000-20000 counts
The most commonly used range is 4-20mA, as it has no voltage drop for longer distances and wire cut can be detected as the minimum signal voltage is 4mA.
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OUTPUT SUB SYSTEMS: The actuating elements (output elements) are wired to the output section. Output are classified into two: 1.Digital 2.Analog 1.Digital Output: These have only two states, viz., ON or OFF (digitally 1 or 0). Therefore these are also called as discrete outputs. These elements are mainly actuators like contactors. Relays, solenoid coils, indicating lamps, annunciation lamps etc., and are directly connected to outputs of the PLC. 2.Analog output: These output have multiple states and rather continuously changing one and are having a range of values. Electrically these are categorized into two. 1. Voltage: The commonly used ranges are 1.0 to 10VDC -unipolar 2.–10 to +10VDC bipolar 3.0 to 5VDC 2. Current: The commonly used ranges are 1. 0 to 20ma 2. 4 to 20ma In case of analog outputs, the digital value is converted to analog signals and these signals are fed to actuators such as control valves. These control valves in turn open / close from 0 to 100% depending on digital values fed. A typical example for analog output is as shown below: 4000-20000 counts to 4 to 20 mA
Analo g output of PLC
Uncontrolled Flow
FLAGS:
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0-100% Controlled Flow
Flags are just like auxiliary relays used in conventional RLC systems (ref. R12 in fig 1.1). These are similar to digital outputs as far as internal execution is considered. These are internal to the system to store temporary digital data (bit 1/0) and will not have any physical output. These will be accessed as bits. REGISTERS: Just as flags are used to store temporary digital data, registers are used to store temporary analog data. These will be used in mathematical calculations, Timers, counters etc. These will be accessed as word, and length of word depends on processor used (for e.g. 16bit, 32 bit etc)
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Wiring of Digital Inputs The field sensing elements such as pushbuttons, Switches etc., are wired as shown in the fig 1.3
1 2 3
In case of AC voltage type Digital input cards, L1and L2 can be fed with line and Neutral. (To remind AC voltage has alternating polarity, hence L1 can either be connected to Line or Neutral with L2 connected the other.)
COM
L1
L2
Fig 1.3
In case of DC voltage type digital input cards, if L1 is connected to 0Vdc and L2 is connected to +Vdc then inputs are called “Sink type inputs”. When the input circuit is completed, +ve signal is available at the channel. The input card converts it to “1” if +ve signal is available and “0” if no signal is available. Hence these are also called “Positive inputs”. If L1 is connected to +ve Vdc and L2 is connected to 0Vdc, then inputs are called “Source type inputs”. When the input circuit is completed, 0Vdc signal is available at the channel. The input card converts it to “0” if 0Vdc signal is available and “1” if no signal is available. Hence these are also called “Negative inputs”. We are positive thinkers and hence the most commonly used input wiring for DC voltage is the sink type. Source type of cards is used when interfacing devices like PNP Proximity sensors. One major advantage of PLC is that, the inputs connected can either be normally open or normally closed. Internally PLC can generate unlimited number of normally open and normally closed contacts from it. If normally open (NO) contacts are wired, then normally the PLC input will be “0”. And when the contact is actuated then the input will be “1”. If normally closed contacts are wired, then normally the PLC input will be “1” and when the contact is actuated then the input will be “0”. Normally NO contacts are used to start applications and NC contacts for stopping. If equipment couldn’t be started then there much less problem, compared to if the equipment could not be stopped. Hence the stop signal should be wired as NC signals as far as possible which then can be termed as “fail safe”. (Note: The most commonly used DC voltage for I/O interrogation is 24v dc)
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Wiring of digital outputs The two most common types of digital outputs are 1.DC type 2.Relay type
1 2 3
COM
L1
L2
Fig 1.3
In case of DC type the field actuators will be connected to the Digital output card as shown in fig1.4. Here, if L1 is connected to +ve Vdc and L2 is connected to 0Vdc then the outputs are called “Source type outputs”. When the output circuit is completed, +ve signal is available at the channel if the PLC writes “1” to the channel and no signal if PLC writes “0” to it. Hence these are also called “Positive Outputs”.
On the other hand, if L1 is connected to 0Vdc and L2 to +Vdc, then the outputs are called “ sink type outputs “. When the output circuit is completed, 0 Vdc is available at the channel if plc writes 1 to the channel and no signal if plc writes 0 to it. Hence these are also called negative outputs. As in the case of inputs most commonly used output wiring for dc voltage is the source type. Sink type outputs are used in specific cases. L1
1
L2 L3
2
L4 L5
3
L6
1
2 3
COM Fig 1.4
L1
L2
Fig 1.5
In case of relay type outputs, there are two types. 1.Isolated type : Here each output is isolated from the other. Hence different voltages can be fed to different channels. These outputs are potential free contacts. Fig 1.4 shows the wiring details of isolated relay type outputs. 2.Non-isolated type: Here all the outputs are grouped into one. Hence only one type of voltage can be fed to the group. Fig 1.5 shows the wiring details of non-isolated or Partially Isolated relay type outputs.
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Wiring of analog input: For 4wire and 2 wire current transducers, the wiring diagram is as shown in Fig1.6 and fig 1.7 respectively. Fig1.8 shows the wiring diagram of voltage transducers to the analog input card. Cable Shield +
Cable Shield +
I ref
Voltage Transducer -
4WT
AC/DC
Ret
Signal Earth
Signal Earth
Analog Input (Current)
Fig 1.6
+
Analog Input (Voltage) Fig 1.8
Cable Shield +
Note:
I ref
+ 2WT -
POWER SUPPLY -
Ret Signal Earth
Analog Input (Current)
Fig 1.7
Analog inputs are like meters, just as voltmeters are connected in parallel and ammeters are connected in series, the wiring to the analog input cards should be done similarly
Wiring of Analog Output: Cable Shield
+
Cable Shield
+
I ref
+
Load
Load -
-
Ret Signal Earth
Analog Output (Current)
Fig 1.9
Signal Earth
Analog Output (Voltage)
Fig 1.10
The wiring for analog output for current and voltage is as shown in fig 1.9 and Fig 1.10 respectively. In case of current analog outputs, the required voltages are generated with the analog signal itself. Tip: In case of analog inputs, wiring should be done in such way considering analog input cards as the measuring meter. On the other hand, in case of analog outputs, wiring should be done in such a way considering the “load” as measuring meter.
There is another classification of PLC input / outputs (I/O). 1.Local I/Os. 2.Remote I/Os.
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1.Local I/Os: If the PLC I/Os are connected directly to the PLC CPU system, then the I/Os are termed as Local I/Os. Fig 1.13 shows the scheme of local P C I I S P / / I/Os. Here all the input and output wiring will be done directly to CPU U U O O system. Fig. 1.13
2.Remote I/Os: C P C O S P M U U M
IU 1
Fig. 1.14
IU 2
IU 3
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
If the PLC I/Os are connected through Remote communication card (COMM) to the PLC system, then the I/Os are termed as of Remote I/Os. Fig1.14 shows the scheme of remote I/Os. Here the I/Os are wired and communicate to the interface unit (IU). These units in turn communicate to the communication card on the PLC system. These I/O’s are interconnected in a daisy chain fashion.
Remote I/Os have following advantages over the local I/Os. • Wiring is minimum, as the I/O wiring is done locally to the equipment. Only one communication cable is used to interface the communication card on the CPU rack and interface unit on the I/O rack remotely placed. Hence cable cost is considerably brought down. • Diagnosis becomes simpler, as the I/O related to the remotely located equipment can be checked near the equipment itself. Various communication protocols (pattern) are used to communicate between the communication cards and interface units. Some of them are Device-net, Profibus etc. Also, there are quite a few proprietary protocols from various manufacturer of the PLC. Efforts are being made to standardize these protocols.
Addressing of Inputs and Outputs in PLC: PLC considers each input, output be it analog or digital or be it flags or registers as different memory location. Various addressing methods are used and
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depend on vendor how they decide to differentiate the different memory locations viz., Digital input, analog input, Digital output, analog output, flags, registers. Also the individual channels can be addressed in different formats viz., 1.Decimal: 1,2,3….9, 10, 11 etc. 2.octal:0, 1, 2,..7,10,11 etc. 3.Hexadecimal: 1,2…9,A, B, C, D, E, F, 10, 11 etc These are prefixed with some characters to differentiate the different I/Os. For e.g.: Digital inputs : X1,X2… Digital outputs: Y1,Y2… Analog Inputs: XX1, XX2…. Analog outputs: YY1, YY2…. Flags: F1, F2…. Registers: R1, R2…. Sample ladder program: Consider the electrical network shown in Fig 1.1. If the same has to be replaced by the plc, then the pushbutton PB1, PB2 would be the inputs and relay coil R1 as output. The auxiliary contactor R12 can be omitted. Suppose PB1, PB2 are connected to 1st and 2nd channel of the digital input card of the PLC and R1 is connected to 1st channel of the digital output card of PLC then the PLC program will be as shown in the above example. X1
X2
Y1
Y1
Fig 1.11
The auxiliary relay R12 in Fig 1.1 is omitted and is replaced by a contact of output itself. This is permitted in PLC. Outputs are memory addresses, which can be read as well as written. Hence if it read, a contact is placed and when it is written a coil is SERVICE placed in the logic. As seen Fig.1.11 looks like a ladder, is why this is termed as HOUSE that KEEPING COMMUNICATIONS ladder program.
PLC SCAN HOW DOES A PLC WORK? INPUT SCAN
OUTPUT SCAN
LOGIC SCAN
Page 10 of 41
Fig 1.12
Most PLC systems execute a scan sequence. Fig 1.12 displays the various blocks in this sequence. House keeping consists of internal checksums and diagnostics that the processor executes every scan cycle. These can be done at the beginning or the end of the scan cycle or both depending upon the PLC. Input scan consists of reading the current state for each input connected to the PLC system and updating the input memory tables (buffer memory). Logic scan consists of reading the use program that has been stored in the PLC memory. These programs can be written in ladder logic, instruction list, sequential Flow charts, function block, structure text, c code or state logic depending upon their manufacturer of the system. Some system supports programming using combination of languages within the same program. Output scan consists of adjusting the values of the outputs connected to the system based upon the status of inputs and execution of the logic. Service communications consists of opening the window of time for the processor to communicate to other devices. These can be programming devices, operator interface devices, remote IO controllers, other PLC’s or any other devices having communication capability that is compatible with the PLC system.
INTRODUCTION TO
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GE FANUC has a wide range of PLC’s catering various sectors of industrial requirements.
90-70 PLC’s for I/Os ranging from 4096 to unlimited.
90-30 PLC’s for I/Os ranging from 16 to 4096
Versamax PLC’s for small & medium applications.
Apart from these, a range of I/O modules from the simple I/O’s to power monitoring systems are available. Built on Microsoft windows platform is the programming software for all these range of PLC’s. GE FANUC has also developed a high powerful Supervisory Control And Data Acquisition (SCADA) Software called the
PLC addressing in GEFanuc PLC’s:
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All addressing in GEFanuc series of PLC’s is in the decimal format. The different memory locations are prefixed with characters as follows 1 Digital input: 2 Digital output: 3 Analog input: 4.Analog output: 5.Registers: 6.Flags: 7.Temporary bits: 8.System bits: 9.Global bits:
%IXXXX %QXXXX %AIXXX %AQXXXX %RXXXX %MXXXX %TXXXX %SXXXX %GXXX
10 Slot Base
90-30 PLC’s: Rack Expansion
Page 13 of 41 Power Supply
CPU
I/Os
Fig 2.1
The different parts of a 90-30 PLC are as shown in Fig 2.1. The base plates are of two types 1 CPU base plates a. IC693CHS397 five slot modular CPU base plate b. IC693CHS391 ten slot modular CPU base plate 2 Expansion base plate a. IC693CHS398 five slot expansion base plate b. IC693CHS3392 ten slot expansion base plate The ranges of power supply modules for 90-30 PLC are as follows: Catalog number IC693PWR321 IC693PWR330 IC693PWR322 IC693PWR328 IC693PWR331 IC693PWR332
Nominal input voltage 100 TO 240 VAC OR 125 VDC 100 TO 240 VAC OR 125 VDC 24 OR 48 VDC 48 VDC 24 VDC 12 VDC
Output voltage +5VDC,15WATTS +5VDC,30 WATTS +5VDC,15 WATTS +5VDC,15 WATTS +5VDC,30 WATTS +5VDC,30 WATTS
The range of CPUs along specification is given as follows CPU type(IC693CPUxxx)
331
Page 14 of 41
340
341
350
351
352
No. Of expansion base plates
4
Load required from +5v dc supply 350ma Processor Speed (mega hertz)
10
4
4
7
7
7
490ma
490ma
670ma
890ma
890ma
20
20
25
25
25
Processor type
80188
Operating temperature (in dg .c)
0- 60
0-60
0-60
0-60
0-60
0-60
Typical scan rate (ms/1k of logic)
0.4
0.3
0.3
0.22
0.22
0.22
16kb
32kb
80kb
32kb
240kb
240kb
Discrete input points-%I
512
512
512
2048
2048
2048
Discrete output points-%Q
512
512
512
2048
2048
2048
Discrete global memory-%G
1280
1280
1280
1280
1280
1280
Internal coils-%M
1024
1024
1024
4096
4096
4096
Output temporary coils-%T
256
256
256
256
256
256
System status reference-%S
128
128
128
128
128
128
2048
9999
9999
9999
16384
16384
128
1024
1024
2048
16384
16384
Analog Outputs-%AQ
64
256
256
512
16384
16384
System registers-%SR
16
16
16
28
28
28
680
>2000
>2000
>2000
>2000
>2000
No
Yes
YES
Yes
Yes
Yes
RAM
RAM
RAM
RAM
RAM
RAM
EEPROM
FLASH
FLASH
FLASH
FLASH
FLASH
1
1
1
1
3
3
No
No
No
No
No
No
User program memory (max)
Register memory-%R Analog Inputs-%AI
Timers/Counters Interrupts Types of memory storage Optional memory No. Of programming ports Built in Ethernet ports
CPU Type (IC693CPUXXX) No of expansion base plates Load required from +5v dc supply
80c188xl 80c188xl 80386ex 80386ex 80386ex
360
363
364
7 670 mA
7 890mA
7 1.51A
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Processor speed (MHz) Processor type Operating temperature in *c Typical san rate (ms/1k of logic) User program memory (max) Discrete input points %I Discrete output points %q Discrete global memory %G Internal coils %M Output (temporary) coils %T System status reference %S Register memory %R Analog inputs %AI Analog outputs %AQ System registers %R Timers / counters Interrupts Type of memory storage Optional memory Floating point math support No. Of programming ports Built in Ethernet port
25 80386EX 0 to 60 0.22 240 kb 2048 2048 1280 4096 256 128 16384 16384 16384 28 >2000 Yes
25 80386EX 0 to 60 0.22 240 kb 2048 2048 1280 4096 256 128 16384 16384 16384 28 >2000 Yes
25 80386EX 0 to 60 0.22 240 kb 2048 2048 1280 4096 256 128 16384 16384 16384 28 >2000 Yes
RAM Flash Yes 1 No
RAM Flash Yes 3 No
RAM Flash Yes 1 Yes
Features of the latest CPU in the market is IC693CPU374 CPU type Processor speed Processor type Typical scan rate Type of memory storage User memory (total) Discrete input points %I
: : : : : : :
Single slot CPU with embedded Ethernet interface 133 MHz embedded 586 0.15 ms/1k of logic (Boolean contacts) RAM and flash 240kb 2048 (fixed)
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Discrete output points % Q Discrete global memory %G Internal coils %M Output (temporary)coils %T System status references % S Register memory %R configurable Analog inputs %AI configurable Analog outputs %AQ configurable System registers % SR Timers/counters Battery backed clock) Load required from power supply Ez program storage device Total base plate per system Interrupt support Floating point math Built in serial ports Built in Ethernet No. of Ethernet ports No. of IP addresses Operating Temperature Storage Temperature
: 2048 (fixed) : 1280 bits fixed : 4096 bits fixed : 256 bits fixed : 128 bits (%S,%SA,%SB,%SC 32 bits each) (fixed) : 128 to 32640 words : 128 to 32640 words : 128 to 32640 words : 28 words (fixed) : > 2000 (depends on available user memory) : yes : 7,4 watts of 5v dc : yes : 8 ( CPU base plate + 7 expansion and /or remote) : supports the periodic subroutine feature : yes, hardware floating point math :supports RS485 port on the power supply : communications Ethernet (built in) 10/100base T/TX Ethernet switch : 2,both are 10/100 base T/TX ports with auto sensing RJ 45 connection :1 :0 to 60 °C (32 to 140 °F) ambient :-40 °C to +85 °C
Types of Discrete/Digital Input Modules:
Page 17 of 41
Types of Discrete/Digital Output Modules:
Types of Discrete Mixed Modules Page 18 of 41
Types of Analog Input Modules:
Types of Analog Output Modules:
Types of Analog Mixed Modules:
LADDER PROGRAMMING:
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As earlier discussed, ladder program is one of the methods of programming the PLC’s. The flow of the program is “Left to right top to bottom” GE Fanuc PLC’s has a powerful set of functions and categorically divided as under 1.Relay functions 2.Timers and counters 3.Math functions 4.Relational functions 5.Bit operation functions 6.Data move functions 7.Table functions 8.Conversion functions 9.Control functions
1.RELAY FUNCTIONS: Relay function is composed of contacts and coils as is so in a relay. Contacts: XXX 1.Logical “Normally Open” contact (NO) A NO contact acts as a switch that passes power flow if associated reference is ON XXX
2.Logical “Normally Closed” contact (NC) A NC contact acts as a switch that passes power flow if associated reference is OFF (Note: XXX means the reference address which can be %I ,%Q,%M,%S, %G or %T)
Example: %I001
%I003 %M0100
%Q010
%S007
%T01
%G02
%Q01
In the above example %Q001 will be ON if %I001, %Q010, %S007 and %G002 is ON (1) and %I003, %M0100 and %T001 is OFF (0) Ladder logic permits only 9 contacts and a coil in series. If the number of contact is more than 9 then, continuation contact Can be used in combination with continuation coil For e.g.: %I001
%I003 %M0100
%Q010
%S007
%T01
%G02
%I05
%I06
<+> %I007
%Q01
<+> Coils: Types of coils: Page 20 of 41
Normally open coil Negated coil. The referenced coil will be ON when the conditions previous to it i.e., the contacts does not satisfy the power flow S
Set coil. The referenced coil will be ON when the conditions previous to it i.e., the contact satisfies. Once the coil is ON, it will remain ON even when the condition previous to it does not satisfy the power flow anymore. The only way to reset the coil is by a reset coil to the same referenced address.
R
Reset coil. The referenced coil, which has been made ON through a set Coil, is made OFF through reset coil. The set and reset coil together form a latch. Positive transition coil. The referenced coil will be ON once the condition (contacts) previous to it satisfy and give a power-flow to the coil. The coil will be ON only for one PLC scan time. For e.g.:
%I001
%Q001
Here %M001 will be ON the moment %I001 is ON only for 1 PLC scan. If %M001 has to become ON again, then %I001 has to go OFF and become ON again. Negative transition coil. The referenced coil will be ON once the condition (contacts) previous does not satisfy and there is power-flow. The coil will be ON only for one PLC scan time. %I001
%Q001
Here %M001 will be ON the moment %I001 is OFF from ON. %M001 will be ON only for 1 PLC scan. If %M001 has to become ON again, then %I001 has to go ON and become OFF again.
Important things to remember when using coils:
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Tip1: Avoid multiple coils of the same referenced address i.e., %I001
%I002
%Q001
%M001
%I004
%Q001
PLC considers the bottom most coil in such case, and the first rung never gets satisfied. If two or more conditions can, make a coil ON, then the logic should be as under: %I001
%M001
%M1001
%I002
%I004
%M1001
%M1002
%Q001
%M1002
Tip2: Coils can be used only for %M, %Q, %T & %G bits. Tip3: Use the %Q bits at the end of the program preferably. It’s a good programming practice.
2.Timers and counters:
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Timers: There are three types of timer functions: Normal timer On-delay timer Off- delay timer Normal timer
TMR Tb Enable
Done ????
???? Tb
PV PV
Enable Done PV ????
- %R reference (3 consecutive) -Time Base 1 tenth, 1 hundredth, 1 thousandth of a second -Preset Value
Necessarily has to be contacts and can be a single or series of contacts. Necessarily has to be a coil Can be a constant or %R reference Must be necessarily %R reference. Once a register is specified, automatically the other 2 consecutive registers are taken. These 3 %R reference should not be used anywhere else in the logic.
Actual time = PV * time base Function: When the timer enable is ON, the “TMR” block starts counting the specified time (PV*Tb). Once the actual time has elapsed, the timer done bit is made ON till the timer enable is ON. If the timer enable is OFF the timer resets to zero.
2. On-delay timer:
Page 23 of 41
Enable
TMR Tb Done
Reset
???? Tb
???? PV
Enable & Reset Done PV ????
PV
- %R reference (3 consecutive) -Time Base 1 tenth, 1 hundredth, 1 thousandth of a second -Preset Value
Necessarily has to be contacts and can be a single or series of contacts. Necessarily has to be a coil Can be a constant or %R reference Must be necessarily %R reference. Once a register is specified, automatically the other 2 consecutive registers are taken. There 3 %R reference should not be used anywhere else in the logic.
Actual time = PV * time base Function: When the timer enable is ON & timer reset is OFF, the “TMR” block starts counting the specified time (PV*Tb). Once the actual time has elapsed, the timer bit is made ON and will remain ON till the timer enable is ON. Incase, If the timer enable is OFF, the timer is counting the on-delay timer retains the elapsed time and will resume counting timer when the enable input becomes ON again. The only way to reset the On-delay timer is by making the timer reset ON. This timer can be used as RETENTIVE TIMER.
3. Off- delay timer Enable
OFDT Tb ????
Page 24 of 41
Done ???? Tb
PV PV
- %R reference (3 consecutive) -Time Base 1 tenth, 1 hundredth, 1 thousandth of a second -Preset Value
Enable Done PV ????
Necessarily has to be contacts and can be a single or series of Contacts Necessarily has to be a coil can be a constant or %R reference Must be necessarily %R reference. Once a register is specified, automatically the other 2 consecutive registers are taken. There 3 %R reference should not be used anywhere else in the logic.
Actual time = PV * time base Function: When the timer enable is ON, timer done is also ON. Once the timer enable is OFF, the “TMR” block starts counting the specified time (PV*Tb). Once the actual time has elapsed, the timer done bit is made OFF and will remain OFF till the timer enable is ON. E.g.: A typical; application is with turbine and its associated lubrication oil pump. The requirement is as long as turbine is running; lubrication oil pump also must be ON. When the turbine stops electrically, lubrication pump should continue to be ON for some time (because turbine is till running mechanically due to moment of inertia). Here OFF delay timer can be used by giving the turbine running contact to timer enable, and lubrication pump output to timer done.
Counters:
Page 25 of 41
There are two types of counters 1. Up counter 2. Down counter Up-counter: Counting Pulse
UPCTR Done
Reset
????
???? PV
- %R reference (3 consecutive) -Preset Value
PV
Counting pulse & Reset Done PV ????
Necessarily has to be a contact Necessarily has to be a coil Can be a constant or %R reference Must be necessarily %R reference. Once register is specified, Automatically the other 2 consecutive registers are taken. These 3 %R reference should not be used anywhere else in the logic
Function: The counter increments by one when, there is a transition high at Counting Pulse input. The initial value of the counter will be zero. Once the counter reaches the PV, the counter dome bit becomes ON. Down-counter: Counting Pulse
DNCTR Done
Reset
????
???? PV
- %R reference (3 consecutive) -Preset Value
PV
Function: Every time the down counter receives a high transition input at the counting pulse, the counter decrements by one. The initial value of the counter will be PV. Once the counter reaches the zero, the counter dome bit becomes ON.
3.Math Functions:
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Before the discussion about Math function, Data types needs to be explained. Data is the operand on which the operation or function is performed. There are various data types. Viz., Int- Signed IntegerSigned integers use 16 bit memory data locations, and are represented in 2’s complement notation. The valid range of an INT data type is – 32,768 to 32,767. Dint- Double Precision Signed Integer Double precision-signed integer is stored in 32 bit data memory locations (actually two consecutive 16 bit memory locations) and represented in 2’s complement notation (Bit 32 is the sign bit) The valid range of a DINT data type is 2,147,483,648 to +2,147,483,647. Bit- bit A bit data type is the smallest unit of memory. It has two states, 1 or 0.A BIT string may have length N Byte- byte A byte data type has an 8-bit value. The valid ranges is 0 to 255 (0 to FF in Hexadecimal) Word- word A word data type uses 16 consecutive bits of data memory; but, instead of the bits in the data location representing a number, the bits are independent of each other. Each bit represents its own binary state (1 or 0) and the bits are not looked at together to represent an integer number. The valid ranges of word values is 0 to FFFF Dword- Double word A double word data type has the same characteristics as a single word data type, except that it uses 32 consecutive bits in data memory instead of 16 bits. BCD-4-Four-Digit Binary Coded Decimal Four-digit BCD numbers use 16-bit data memory locations. Each BCD digit uses four bits and can represent numbers between 0 and 9. This BCD coding of the 16 bits has a legal value range of 0 to 9999. Real-Floating point. Real numbers use 32 consecutive bits (actually two consecutive 16-bit memory locations). The range of numbers that can be stored in this format +/- 1.401298 E-45 to +/- 3.402823 E+38
The various Math functions available in 90-30 PLCs are:
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Standard Math Functions: ADD (Addition) SUB (Subtraction) MUL (Multiplication) DIV (Division) MOD (Modular Division) – division to obtain the reminder E ???? ????
I1
XXX YYY
PF
???? Q
I2
EEnable PF- Power flow XXX- Function name (Add, Sub, etc) YYY- Data type I1- Operand1 I2- Operand2 Q- Result of (I1 function I2) ADD, SUB, MUL & DIV operate on INT, DINT & REAL data types. MOD operates only on INT & DINT data types. Note: PF can be used as enabling conditions for a cascaded function. Special Math functions:
1. SQRT- Square root 2. SIN, COS, TAN, ASIN, ACOS, ATAN- Trignometric functions 3. LOG, LN, EXP, EXPT- Logarithmic/exponential Functions. 4. RAD, DEG- Radian conversion Functions
E
????
PF
XXX YYY
IN
Q
????
E- Enable PF- Power flow XXX- Function name (LOG, SQRT, etc) YYY- Data type IN- Operand Q- Result of (Function (IN)) SQRT operate on INT, DINT & REAL data types. Other functions operate only on REAL data types.
4.Relational Functions: Relational Functions are used to determine the relationship of two values. Standard Relational EQ (Equals to)
E- Enable XXX- Function name (EQ, GE, etc) Functions:YYY- Data type I1- Operand1 I2- Operand2 Q- ON if (I1 function I2) is true
GT, GE, LT, & LE operate on INT, PageEQ, 28 NE, of 41 DINT & REAL data types.
NE (Not Equal to) GT (Greater than) GE (Greater than or equal to) LT (Less than) LE (less than or equal to)
E
XXX YYY
????
Q
I1
????
I2
Range Relational Function:
1. Range (Greater than low limit and less than high limit)
???? ???? ???? L2
E- Enable YYY- Data type L1- Lower limit L2- Upper limit IN- Data Input Q- ON if (IN is > L1 and < L2)
RANGE YYY L1 Q IN
Range function operates on INT, DINT & WORD data types. Note: “ Q “ can be given to a coil or can be used as an enable input to the next cascaded function.
5.BIT Operations Logical: AND, OR, XOR E ???? ????
I1
XXX YYY
????
PF
Q I2
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E- Enable PF- Power flow XXX- Function name (AND, OR etc) YYY- Data type is always WORD I1- Operand1 I2- Operand2 Q- Result of (I1 function I2)
NOT E ????
NOT WORD I1
PF ????
Q
EEnable PF- Power flow I1- Operand1 Q- Result of (I1 NOT) Note: PF can be used as enabling conditions for a cascaded function.
SHIFT: When enabled, the group of bits at “IN” are shifted “N” times in the direction specified. When shifted, the result is placed in “Q”. “B2” provides power-flow based on last bit shifted out.
E ???? ???? ????
EPF-
XXX YYY IN LEN B2
????
N B1
Q
PF ????
Enable Power flow
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XXX- Function name (SHL / SHR) YYY- Data type is always WORD IN- Operand N- Number of times to be shifted Q- Result after shift LEN-1 to 256 ROTATE: When enabled, the group of bits at “IN” are rotated within the group “N” times in the direction of the rotate. The bits shifted out goes to “Q” and to the other end of the group. Power-flow occurs after the instruction when enabled. E ???? ????
XXX YYY
PF
LEN ???? IN
N
???? Q
EEnable PF- Power flow XXX- Function name (SHL / SHR) YYY- Data type is always WORD IN- Operand N- Number of times to be shifted Q- Result after shift LEN-1 to 256 BIT TEST: When enabled, the bit specified at “BIT” within the group at “IN” will be tested. The results will be indicated with power-flow at “Q”. E ???? ????
E- Enable IN- Operand BIT- Bit to be tested Q- Result (1 if Tested bit is ON, 0 if Tested bit is OFF) LEN- 1 to 256
BIT TEST LEN WORD ???? Q IN
BIT
BIT
MANUPULATION:
BITSET, BIT RESET When enabled, the bit specified at “BIT” will be set or cleared. If enabled and the “BIT” is within the group of bits, power-flow will occur after the instruction. E- Enable XXX- BIT_SET, BIT_CLR IN- Operand BIT-31Bit Page of to 41be manipulated LEN- 1 to 256
E ???? ????
BIT
XXX WORD LEN Q IN
????
POSITION:
BIT
When enabled, the group of bits specified at “BIN” will be searched for an “ON” condition. When found, the bit number will be placed in “POS”. Power-flow after the instruction will occur when enabled. E
XXX LEN WORD
???? ????
???? IN
E- Enable XXX- BIT_POS IN- Operand POS- Bit position LEN- 1 to 256
POS
BIT SEQUENCER: The Bit Sequencer (BITSEQ) function performs a bit sequence shift through an array of bits. E R ???? ???? ????
LEN
Length specifies the number of bits (starting at ST) that this instruction will step through. Acceptable values range from 1-256. Add The control word for the BIT_SEQ function. The default data type is BIT_SEQ. This data type is 3-words long. Current step number = word 1. Length of sequence in bits = word 2. Control word = word 3. R When R is energized, the bit sequencer's step number is set to the value in STEP (default = 1), and the bit sequencer is filled with zeros, except for the current step number bit. DIR When DIR is energized, the bit sequencer's step number is incremented prior to the shift. Otherwise, it is decremented. N When R is energized, the step number is set to this value. ST ST contains the first word of the bit sequencer.
BITSEQ LEN ???? R DIR STEP
Add ????
ST
6.DATA MOVE: MOVE: Source to Destination E
MOVE LEN XXX ????
????
???? IN
Q
E- Enable XXX- INT, BIT, WORD,REAL IN- Source LEN- 1 to 256 Q- Destination
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BLOCK MOVE: Source to Destination E ???? ???? ???? ???? ???? ???? ????
BLKMV XXX IN1 IN2 IN3 IN4 IN5 IN6 IN7
???? Q
E- Enable XXX- INT, WORD, REAL IN1 to 7- Source & Constant Q- Destination
BLOCK CLEAR: Source to Zero E
E- Enable XXX- WORD IN- Source LEN- 1 to 256
BLKCL LEN R ???? XXX
????
SHIFT same E R
IN
REGISTER: Shift data words or bits to a new memory location or in the memory location.
SHFR LEN XXX ????
???? ????
???? IN
Q
ST
E- Enable R- Reset XXX- BIT, WORD IN- Source LEN- 1 to 256 ST- First bit or word of the shift register Q- Contains the bit or word shifted out of the shift register. For variables of type BIT, any discrete reference may be used.
COMMREQ: Use the COMMREQ function to send a command request to specialty modules like the Genius Bus Controller, Ethernet Interface, CMM or PCM modules. When the COMMREQ receives power flow, the command block defined by IN is sent to the specialty module located at the rack/slot location specified by the SYSID parameter. E ????
IN COMM REQ
????
IN
????
SYS
Contains the location of the command block. Refer to the documentation for your specialty module to define the command block. Data Type: WORD SYSID Contains the rack/slot location of the intelligent module. Data Type: WORD TASK Contains information specific to your specialty module. Refer to the documentation for your specialty module to define this field. Data Type: WORD FT FT is energized if the COMMREQ fails.
TASK
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7.TABLE FUNCTIONS: ARRAY MOVE(BOOL,BYTE,INT,DINT & WORD): The Array Move (Array Move) function to copy a specified number of data elements from a source array to a destination array. The Array Move function has five input parameters and two output parameters. When the function receives power flow, the number of data elements in the count indicator (N) is extracted from the input array starting with the indexed location (SR + SNX – 1). The data elements are written to the output array starting with the indexed location (DS + DNX – 1). The variable length specifies the number of elements that make up each array. E R ???? ???? ????
XXX ARRAY MOVE LEN XXX ???? SR SNX DNX N
SR Data SNX Data DNX Data N Data DS
The length specifies the number of elements (starting at SR and DS) that make up each array. SR contains the starting address of the source array. For an Array Move with the data type BIT, any reference may be used; it does not need to be byte aligned. Types: WORD, WORD Length 2, BIT, and BYTE SNX contains the index of the source array. Type: WORD DNX contains the index of the destination array. Type: WORD N provides a count indicator. Type: WORD DS contains the starting address of the destination array. For an Array Move with the data type BIT, any reference may be used; it does not need to be byte aligned.
Data Types: WORD, WORD Length 2, BIT, and BYTE
SEARCH (BOOL,BYTE,INT,DINT & WORD):
The Search function to search a value in a array of values. This search function has four input parameters and two output parameters. When the function receives power, the array is searched starting at (AR + INX). This is the starting address of the array (AR) plus the index into this array (INX). The search continues until condition of the search object (IN) is found or until the end of the array is reached. If an array element is found, output parameter (FD) is set ON and output parameter (ONX) is set to the relative position of this element within the array. If no array element is found before the end of the array is reached, then output parameter (FD) is set OFF and output parameter (ONX) is set to zero.
E ???? ???? ????
XX
SEARCH YY XX AR INX IN
Length. The length specifies the number of elements (starting at AR) that make up the array to be searched. Acceptable values range from 1-32767. AR AR contains the starting address of the array to be searched. Data Types: WORD, WORD Length 2, and BYTE INX Input NX (INX) contains the index into the array at which to begin the search. Data Type: UINT IN IN contains the object of the search. Data Types: WORD, WORD Length 2, and BYTE ONX Output NX (ONX) holds the position within the array of the search target. Data Type: UINT FD FD indicates that an array element has been found and the function was successful. YY Page 34EQ, ofNE, 41 GT, GE, LT & LE.
8. CONVERSION BCD4 to INT, BCD4 to REAL, DINT to REAL, INT to BCD4, INT to REAL, REAL to DINT, REAL to INT, REAL to WORD, WORD to REAL CONVERSIONS. E
XXX XXX
????
IN Q IN
Q
CONVERSION BCD4 to INT, BCD4 to REAL, DINT to REAL, INT to BCD4, INT to REAL, REAL to DINT, REAL to INT, REAL to WORD, WORD to REAL. INPUT DATA OUTPUT DATA AFTER CONVERSION
Data Types: WORD, WORD Length 2, BIT, and BYTE
9. CONTROL CALL: To call Ladder blocks. E
CALL
. Blocks should exist in the folder prior to making the Call. ·The PLC will only allow a maximum of 8 nested calls before an "Application Stack Overflow" fault is logged and the PLC transitions to STOP/FAULT mode. ·You can use up to 64 blocks in a folder (subject to available memory). The maximum number of block calls within a given block is 64. The maximum number of calls to a particular block is 255. (A block can be executed any number of times, but there can be no more than 255 explicit calls to any given block.)
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PID (ISA,IND): For Proportional Integral & Derivative closedloop control algorithms. The PID function is designed to solve one loop equation in one execution. The function block data uses 40 registers in a loop data table. The first 35 registers are reserved for the function and should not be used by any application. The last 5 registers are reserved for external use. Registers cannot be shared. If there are multiple occurrences of the same PID function controlling multiple loops, each occurrence requires a separate block of 40 registers. The PID function has six input parameters: a process set point (SP), a process variable (PV), a manual/auto Boolean switch (MAN), a manual mode up adjustment input (UP), and a manual mode down adjustment (DN). It also has an address, which specifies the location of a block of parameters associated with the function. It has two output parameters, a successful Boolean output and the control variable result (CV). If power flow is provided to the Manual input contact, the PID block is placed in Manual mode and the output Control Variable is set from the Manual Command parameter %Ref+13. If either the UP or DN inputs have power flow, the Manual Command word is incremented or decremented by one CV count every PID solution. For faster manual changes of the output Control Variable, it is also possible to add or subtract any CV count value directly to/from the Manual Command word. VersaPro allows you to tune PID instructions in real-time. Series 90 PLCs use the Proportional plus Integral plus Derivative (PID_ISA and PID_IND) function for control of real time processes. To access the Tuning Parameters dialog box, choose Tuning Parameters from the PLC menu. Use the Tuning Parameters dialog box to customize operation of the PID loop in your application. the following describes each field that appears on this dialog box. Loop No. (Loop number) Uniquely identifies the PID block for reference by external devices, operator interfaces. Manual Command If the PID block is in Automatic mode, this value is set to the current CV output. If the PID block is switched to Manual mode, this value is used to set the CV output and the internal value of the integrator, within the Upper and Lower Clamp and Slew Time limits. Control This internal parameter is normally set to 0. If Override is ON, these bits and internal SP, PV and CV words will be used for remote operation of this PID block. This allows operator interface devices, such as a computer, to control the PID loop remotely. CAUTION: If you do not want to enable remote control, set Override to OFF. Enable: Tracks the enable input into the function block and is used to determine whether or not the function block is active.
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Override: Enables remote control of the PID block. If Override is OFF (default), use the other control bits to track the status of the PID input contacts. If Override is ON, the PID function will be controlled by remote devices by modifying internal SP, PV and CV words. When the override bit is ON, the function block executes based on the current values of manual, up, and down, that is, the next three fields. When the override is OFF, the manual, up, and down values are set to the values as defined by the function block's discrete inputs. Manual: If ON, block is in manual mode. If OFF, block is in automatic mode. Up: If ON and Manual is ON, CV is incremented every solution. Down: If ON and Manual is ON, CV is decremented every solution. Tuning Proportional (Proportional Gain): Sets the proportional gain (0.01 seconds timebase). Derivation (Derivation Gain): Sets the derivation gain (0.01 seconds timebase). Integral (Integral Rate): Sets the integral rate with a timebase of .001 repeats per second. SP, PV and CV Percentage Bar Graphs Calculated based on the SP (Set Point Value) and PV (Preset Value) values. The maximum and minimum scale values are set by the user. CV graph is calculated based on the value of CV (Current Value) and the lower and upper clamp parameters. SP/PV Range Optional integer values in PV Counts that define the highest and lowest display value for the SP and PV bar graphs. SP Value Represents the process Set Point input. In PID control, the loop adjusts the output CV so that PV matches SP. Sample Period Shortest time, in 10 millisecond increments, between solutions of the PID loop. If 0, the loop is solved every time the block is called. Note: The PID loop is solved only if the current PLC elapsed time clock is at or later than the last PID solution time plus this sample period. The PLC sweep time should be less than 10% of the sample period to ensure a regular solution time. If not, the sample period should be set to 0.00, specifying execution every sweep. Bias A value (in CV Counts) added to the PID Output before the rate and amplitude clamps. It can be used to set non-zero CV values if using only Kp Proportional gains, or for feed forward control of this PID loop output from another control loop. The usual setting for the Bias field is +16000 to let the function regulate error around the output midpoint. Dead Band Upper and Lower Integer values defining the upper and lower dead band limits. If no dead band is required, set these two values to 0. Read the following notes if setting dead band limits: 1.If the PID Error (SP - PV) or (PV - SP) between the dead band limits, the PID calculations are solved with an Error of 0. 2.If setting the dead band limits, Dead Band Upper must greater than 0 and Dead Band Lower must be less than 0 or the PID block will not function.
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3.You should leave the dead band limits set to 0 until the PID loop gains are setup or tuned. It may then be desirable to add Dead Band to avoid small CV output changes due to small variations in error, perhaps to reduce mechanical wear. Upper Clamp and Lower Clamp Integers (in CV Counts) that define the high and low values for CV. The clamps are used to define limits based on physical limits for a CV output. The Upper Clamp must have a more positive value than the Lower Clamp, or the PID loop will not work. The PID block has anti-reset windup to modify the integrator value when a CV clamp is reached The upper clamp is usually set to +32,000 to allow the CV output to take on the full range of values. Error Term Selects how the error will be calculated. Min Slew Time Defines the minimum number of seconds for the CV output to move from 0 to full travel of 100% or 32000 CV Counts. It is an inverse rate limit on how fast the CV output can be changed. If positive, CV cannot change more than 32000 CV Counts times Delta Time (seconds) divided by Minimum Slew Time. For example, if the Sample Period was 2.5 seconds and the Minimum Slew Time is 500 seconds, CV cannot change more than 32000*2.5/500 or 160 CV Counts per PID solution. As with the CV Clamps, there is an anti-windup feature that adjusts the integrator value if the CV rate limit is exceeded. If Minimum Slew Time is 0, there is no CV rate limit. Note: Make sure you set Minimum Slew Time to 0 while you are tuning or adjusting PID loop gains. Derivative Action Selects how the derivative action is applied. Output Polarity Selects the output polarity of the CV. Update Folder Button Saves values which have been edited in the dialog box to the stored value field of the PID variable. Clicking this button will cause the PLC status to become Not Saved. In order for this button to function, the variable assigned to the Address parameter must have a length of 40 words. If you are online and equal, you will have to rebuild your equipment folder, then Verify equality or Check All to regain equality with the attached PLC. Update PLC Button If you are online and equal with the PLC CPU, click this button to update edited values in the PLC. There are two types of algorithm ( INDEPENDENT & ISA) 1.The Independent term PID (PID_IND) algorithm calculates the output as: PID Output = Kp * Error + Ki * Error * dt + Kd * Derivative + CV Bias 2.The standard ISA (PID_ISA) algorithm has a different form: PID Output = Kc * (Error + Error * dt/Ti + Td * Derivative) + CV Bias
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Fault diagnosis & Troubleshooting For PLC diagnosis & troubleshooting, The Series 90 PLCs maintain two fault tables, the I/O fault table for faults generated by I/O devices (including I/O controllers) and the PLC fault table for internal PLC faults. Both tables contain similar information. The fault data in these tables only exists in the PLC. • The PLC fault table contains: . Fault location. . Fault description. . Date and time of fault. Stores upto 16 fault entries, 8 Oldest and 8 latest. After 16 faults, the latest fault entry is over-written on to the 16th fault, with 16th shifting to 15th and downwards until the 9th fault entry. The 9th entry is over-written by the 10th, thereby deleting the 9th entry. • The I/O fault table contains: . Fault location. . Reference address. . Fault category. . Fault type. . Date and time of fault. Stores upto 32 fault entries, 16 Oldest and 16 latest. After 32 faults, the latest fault entry is over-written on to the 32nd fault, with 32nd shifting to 31st and downwards until the 17th fault entry. The 17th entry is over-written by the 18th, thereby deleting the 17th entry. The system status can also be monitored by the help of System reference bits: System reference bits are internal bits used to indicate PLC status. The system reference bits are assigned to the %S data memory type. The %S(System status table) is divided into four groups: %S1 to %S32, %SA1 to %SA32, %SB1 to %SB32 and %SC1 to %SC32. %S1 through %S32 are set by the PLC and are defined in the table below
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The references in the %SA, %SB and %SC tables are used to indicate system and I/O faults. Faults are segregated Fatal faults: Faults that halt the system (Drop the CPU out of RUN Mode), set the Corresponding system references and are logged to the fault table. Diagnostic faults: These faults do not halt the system, but they do set the appropriate system references and are logged to the fault table. Information faults: These faults do not halt the system, but they are logged to the fault tables.
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