The Performance index of programmablecontrollers (PLC-MIX)

March, 2007

The Japan Electrical Manufacturers’ Association

P L C

技 術 専 門 委 員 会

The Programmable Controller Technical Committee

1目次ページ

1.

The reference system in calculation of “PLC-MIX” ····················································································································· 1

2.

The reference distribution ratio of the operation processing instruction classification

3.

Definition ························································································································································································· 24.

5.

in calculation of "PLC-MIX" ·········· 1a)

PLC-MIX ·········································································································································································· 2b)

Basic PLC-MIX ································································································································································· 2c)

Application PLC-MIX ······················································································································································· 2d)

Total PLC-MIX ································································································································································· 2e)

Instruction·········································································································································································· 2f)

Equivalent application instruction. ····································································································································· 3g)

Changed state – Unchanged state ······································································································································· 3h)

Executed state – Unexecuted state.····································································································································· 3i)

Instruction distribution ratio··············································································································································· 3

Calculation of PLC-MIX ································································································································································· 5a)Application instruction······················································································································································· 5b)

Notes: Calculating processing times··································································································································· 5

Evaluation of PLC-MIX in program language other than a ladder logic language··································································· 5a)

Structure text (ST) language··············································································································································· 6b)

Functional block diagram (FBD) language························································································································ 6c)

Simple equivalent application instruction ··························································································································· 72

Introduction
Japan Electrical Manufacture's Association introduces "PLC-MIX" as general Performance index that helps users to choose
suitable PLC in each industrial application.
Total performance of PLC includes not only the operation processing performance that PLC-MIX focuses its attention on but
also communication with peripheral devices, network processing, diagnostics and input and output processing. User should referto information of a manufacturer about these performances individually.

1.

The reference system in calculation of “PLC-MIX”
Since the comprehensive processing performance of PLC is influenced by the system configuration. The reference system

configuration is defined in PLC-MIX in order to eliminate the influence of system configuration. Table 2 shows reference
system configuration.
Table 1
Item

Reference system configuration
Contents

NoteLanguage

Ladder Logic language

IEC61131-3 conformity

System scale

128 inputs / 128 outputs

Direct I/OInternal data

64 words

WORD

width

depends

onthesystem.
Application

8,000 steps (Equivalent)

Basic instruction

Floating-point instructions are not

Application instruction

included.

Instruction

The reference distribution ratio of the operation processing instruction classificationin calculation of "PLC-MIX"
2.

Since application influences the processing performance of PLC, PLC-MIX adopts the average of the instruction distribution
ratio from the application programs used in real industrial fields as shown in Table 2.

1

Table 2 Applications
Industry

Equipment surveillance and control

Application

The number ofsystems

Equipment Monitoring

4

Electric energy Monitoring

1

Operation Panel

1

Line control

8

Steel mill control

1

Materials handling machine4

Conveyor control

1

Printing machine

5

Metalworking

3

Extrusion machine

3Lathe1

Food processing

1

Cultivation monitoring

1

SemiconductorBasic instruction rate

Standard deviation

69.3%

21.9%

78.5%

10.4%

76.85%

10.4%

74.15%

2.5%

60.8%

12.4%

79.2%

5.18%

486.4%

5.72%

38

67.4%

9.09%

Line control

Materials handling machine

Paper manufacture / printing machine

Converting machinery

Food and packaging machinery
A semiconductor and liquid crystal
manufacture equipment
Total

3.

Definitiona)

PLC-MIX
It is the number of the instructions that PLC can carry out in the unit time and it is weighted according to the instruction
distribution ratio. It provides one performance index of PLC instruction processing.

b)

Basic PLC-MIX
It is the number of instructions by which gives the index of the operation processing performance of PLC. It is the numberof the Basic instructions that PLC can carry out in the unit time and it is weighted according to the instruction distribution
ratio of the basic instructions such as input and output for one bit, timers and counters.

c)Application PLC-MIX
It is the number of instructions by which gives the index of the operation processing performance of PLC. It is the numberof the Application instructions that PLC can carry out in the unit time and it is weighted according to the instruction

distribution ratio of the basic instructions of the various operations to WORD (16 bits and 32 bits), transmission, etc.
d)

Total PLC-MIX

It is the number of instructions by which gives the index of the operation processing performance of PLC. It isthe number of the instructions that PLC can carry out in the unit time and it is weighted according to theinstruction distribution ratio of all instructions.
e)Instruction

The instruction of PLC-MIX is based on the ladder Logic language provided in Chapter 4 of IEC61131-3(programmable controller program language).

2f)

Equivalent application instruction.
PLC-MIX is based on the ladder Logic language that is very popular in the industry. However, an equivalent application

instruction is defined to calculate PLC-MIX in PLC that uses the application program by the structure text (ST) language or afunctional block diagram (FBD) language.
g)

Changed state – Unchanged state
PLC is a Change state when an output state is reversed. and It is an unchanged state when an output state is the same before

and after execution of an instructionh)

Executed state – Unexecuted state.
Execution state is a state where an instruction is executed according to the logical true input of the instruction.
Unexecuted state is a state where an instruction is not executed according to the logical false input of the instruction.

i)Instruction distribution ratio
The table 3 shows the distribution ratio of the instruction used for calculation of PLC-MIX from the average of 38 application

programs used in real industrial field.

3

Table 3 Instruction allocation sheet
Instruction
classification

Instruction

Instruction ratio

Input

1-bit external input

Output1-bit external output
Inside input of 1 bit

Basic
instruction

Operation

Inside output of 1 bit

16-bit timer
A timer/counter
16-bit counter
16-bit transmission

16-bit transmission
16-bit addition
16-bit subtraction

16 bits
Four operations
16-bit multiplication
16-bit division
16-bit BCD conversion
16-bit conversion
16-bit BIN conversion
16 bit comparisons
16 bits
Logical operation
16-bit logic

Application
instruction
32-bit transmission

32-bit transmission
32-bit addition
32-bit subtraction

32 bits Fouroperations
32-bit multiplication
32-bit division32-bit BCD conversion
32-bit conversion
32-bit BIN conversion
32 bit comparisons
32 bits
Logical operation
32-bit logic

4-18.399%Changed0.774%

Unchanged

6.969%-30.353%

Changed6.618%

Unchanged

19.855%Unexecuted.

0.438%

Inside of a time

0.438%

After rise

0.438%

Under a count0.012%

Unexecuted.

0.104%

Executed

0.724%

Unexecuted.

2.895%

Executed

0.158%

Unexecuted.

0.631%

Executed

0.074%

Unexecuted.

0.297%

Executed

0.037%

Unexecuted.

0.149%

Executed

0.010%

Unexecuted.

0.041%

Executed

0.007%

Unexecuted.

0.030%

Executed

0.010%

Unexecuted.

0.041%Executed

0.678%

Unexecuted.

2.713%

Executed

1.092%

Unexecuted.

4.368%

Executed

0.067%

Unexecuted.

0.267%

Executed

0.041%

Unexecuted.

0.163%

Executed

0.024%

Unexecuted.

0.097%

Executed

0.040%

Unexecuted.

0.160%

Executed

0.087%

Unexecuted.

0.349%

Executed

0.002%

Unexecuted.

0.010%

Executed

0.002%

Unexecuted.

0.008%

Executed

0.065%

Unexecuted.

0.258%

Executed

0.001%

Unexecuted.

0.005%

84.399%15.601%

4.

Calculation of PLC-MIXa)

Application instruction
An application instruction of the various operations to WORD (16 bits and 32 bits) is depend on the PLC architecture.

PLC-MIX is calculated as one application instruction with a series of operation to access to the data for operation, to execute theoperation, and to storing the operation result. When an equivalent operation is realized by two or more instructions, thoseinstruction executed time are summed and it is considered as an equivalent instruction executed time.
Example 1 When on instruction performs to access to the data for operation, to execute the operation, and to store the result,the processing time is the executed time of the instruction.

ADDAB C

Example 2 When accessing each data, executing the operation, and storing the result are carried out by individualinstructions, the execution time is summation of each instruction processing time.

b)

Notes: Calculating processing times
1) When the operand influences the processing time, the shortest processing time is adopted.
2) When a 16-bit instruction does not exist, the executed time of a similar instruction is adopted (for example, =, ≧ and alogical product instruction, Not-exclusion logical sum, etc.).
3) When a 32-bit instruction does not exist, a time that is 1.8 times as long as the 16-bit instruction is adopted.
4) When the value of the unexecuted state is unknown, (NOP processing time)×(the number of instruction steps) is adopted
as an equivalent value.
5) When an unchanged state processing time of an external output is unknown, the value of changed state is adopted.
6) When the processing time after set of a timer is unknown, the value under count is adopted.
Equivalent operation processing time is sometime not equal to actual value, it is recommended to contact withmanufacturer representatives.

5.

Evaluation of PLC-MIX in program language other than a ladder logic language
In program language other than the ladder logic language provided in IEC61131-3, PLC-MIX is computed by equivalent

Executed total time of the instruction group, that is realizing a series of operation to access to the data for operation, Executed ofoperation, and storing of an operation result for an application instruction as an equivalent application instruction. Moreover,about Executed and unexecuted states, the influence of the discriminate operation for the equivalent instruction (group) shall beconsidered,
The following examples show how to calculate an equivalent execution time for an addition instruction.

ADD

A B C5a)Structure text (ST) language
Example:The figure shows instructions by ST language equivalent to the above 16-bit WORD addition instruction of ladder
Logic Language.
VAR_INPUTENABLE: BOOL;
END_VAR
VAR
A,B,C: INT;END_VARIF ENABLE=1 THEN
C: =A+B;
END_IFIn the above example, an equivalent execution time is considered as executed state when a value of ENABLE is 1,and it is considered as unexecuted state when a value of ENABLE is 0.

The value of ENABLE

Executed time

1

Executed state.

0

Unexecuted state

Functional block diagram (FBD) languageb)

ExampleThe figure shows instructions by FBD language equivalent to the above 16-bit WORD addition instruction ofladder Logic Language

A function block element with the ENABLE (EN) terminal for executed / unexecuted state is an equivalent application
instruction.

In the above example, an equivalent execution time is considered as executed state when a value of ADD_EN is 1, and it isconsidered as unexecuted state when a value of ADD_EN is 0.
.
The value of ADD_EN

Executed time

1

Executed state.

0

Unexecuted state6c)Simple equivalent application instruction
Simple equivalent application instruction Simple equivalent application instruction is defined as an equivalent application

instruction without discriminate operation of executed/ unexecuted state. It provides simple evaluation, while it is not easy tocalculate the execution time of an equivalent application instruction in the ST language or FBD language that has a mechanism
to discriminate an executed state.
An execution time of a simple equivalent application instruction is not identical to one of the equivalent application
instruction, because it does not take count of executed/-unexecuted state.
Example 1 The simple equivalent application instruction of a 16-bit WORD addition instruction in Structure text (ST) language
VAR
A, B, C; REALEND_VAR
C: =A+B;
END

Example 2 The simple equivalent application instruction of a 16-bit WORD addition instruction in Functional block (FBD)
language

A+B

7C