Overview of Mitsubishi PLC and its basic function blocks

PLC (Programmable Logic Controllers) Mistubishi
1

Mitsubishi Electric was established on Jan 15, 1921.

The primary purpose is to focus on home appliances, elevator systems, and industrial automation.

Various types of Mitsubishi PLC controllers and it software features

How the Mitsubishi PLC is selected?

Based on the type of power supply, total number, and type of inputs and outputs used.

Mitsubishi Electric has developed a wide variety of PLC series such as the A-series, FX series, GX series, L series, QS/WS series, and iQ series.

Consider the Mitsubishi PLC having model number

FX3G-48MT/ESS

The FX3G is Series Model.

  • 48 Total number I/O’s (36+24)

  • (24 input point’s 24VDC (sink/source) type, and 24 output points Transistor (source) type)

  • M is Microprocessor unit.

  • T is Transistor type output.

  • E is AC Power Supply.

  • SS is Transistor source output.

The program memory of the Mitsubishi PLC:

It has a large program memory of 64K points

Auxiliary relays 7,680
Timers 320
Counters 235
Data registers 8,000
Extension registers 24,000
Extension file registers 24,000
Total 64,235

How to select a PLC? List of PLC manufacturers

Which programming language is used in PLC?

Ladder Diagram is the most common programming language used for programmable logic controllers.

But it can also handle other languages like Sequential Functional charts, Functional Block Diagram, and Structured Text.

What is the execution time of each instruction?

The execution time of each instruction is

  • 0.21 microseconds for basic contact type instruction.

  • 0.5 microseconds for applied type instruction.

What are the input and output addresses in Mitsubishi PLC?

  • Digital Input:

The PLC input addresses are octal with the prefix “X”, the input addresses are X0 to X7, X10 to X17, and X20 to X27

  • Digital Output:

The PLC output addresses are octal with the prefix “Y”, the output addresses are Y0 to Y7, Y10 to Y17, and Y20 to Y27.

  • Analog Input:

Need to read control register using “From” instruction.

  • Analog Output:

Need to write control register using “To” instruction.

What are the basic function blocks in Mitsubishi PLC?

  1. Timers
  2. Counters

Timers in Mitsubishi PLC:

  • The timer instruction is most commonly used in PLC programming.

  • The timer set to 1 at specific time intervals is called preset time.

  • The timer starts running until the presetvalue is reached.

  • The timer stops running when the preset value becomes equal to the actual value.

  • The timer address starts with the device number, and the preset time and output coil represent the timer in a program.

  • Output coil represents the timer in a program.

  • For declaration of the timer, insert a coil and declare the timer number and preset value (T0 K50) separated by a space. Where T0 timer number and K50 is the preset value of the timer.

  • The timer addresses are T0 to T320.

  • For timers: Time Delay = Time Base * Preset value

  • Time Done bit: TX

  • Where X is the address of timer used.

Range of the timer:

  • The maximum allowable range of unsignedinteger-type timers is K1 to K32767.

  • For a low-speed (100 ms) timer the maximum to the minimum value of time is 0.1 to 3276.7s and

  • For a high speed (10 ms) timer the maximum to the minimum value of time is 0.01 to 327.67s.

Timer instruction Parameter:

  • Timer number: it is an identification number to declare the timer like T0, T1, up to T2047.

  • Preset time: preset time is the duration of the timer. It indicates the unit of time-based. For a low-speed timer the preset value of K30. So the timer runs for 3 sec.

Preset timers are integer values, so we can define our timer preset values 1 to 32767.

The timer can be defined by device K or D. If we want to change our value by HMI, SCADA device ‘D’ is defined.

What are the types of timers available in Mitsubishi PLC?

  • Mitsubishi PLC has four types of timers.

  • The low-speed timer counts time in increments of 100 ms.

  • Low-speed retentive timer: accumulates time in increments of 100ms.

  • The high-speed timer counts time in increments of 10 ms.

  • High-speed retentive timer: accumulates time in increments of 10ms.

Low-speed timer

  • The low-speed timer, counts time in increments of 100 ms.

  • A low-speed timer base is 100ms, if the preset value is K100 then the timer runs only for 10 seconds.

  • Low-speed timer address T0 K100

  • Where T5 is timer number and K100 timer preset value.

  • In this example, the T0 timer number and K50 is the timer preset value. In the next rung, the timer address is used as ‘NO’ contact. If the input of X0 is HIGH then the timer starts for a defined preset value, when the timer reaches a preset value then the output of the timer is set to true otherwise false.

image

High-speed timer

  • High-speed timer counts time in increments of 10 ms.

  • At highspeed the timer base is 10ms, if the preset value is K100 then the timer runs only for 1 second.

  • High-speed timer address H T1 K100

  • Where H: high-speed timer. T1 timer number. K100 timer preset value.

  • In this example, T1 is the timer number and K50 is the timer preset value. In the next rung, the timer address is used as ‘NO’ contact. If the input of X1 is HIGH then the timer starts for a defined preset value, when the timer reaches a preset value then the output of the timer is set to true otherwise false.

image

  • To address a high-speed timer insert an output coil and address a high-speed timer: H, timer address, and preset value separated by a space for example “H T1 K50”

Low-speed retentive timer

  • Insert an output coil and address a low-speed retentive timer and preset separated by a space for example “ST0 K30”.

  • ST0 is a retentive timer number.

  • K30 timer preset value.

image

High-speed retentive timer

  • High-speed retentive timer is the same as a low-speed retentive timer except for the base.

  • A high-speed retentive timer accumulates time in increments of 10ms.

  • Insert an output coil and address a high-speed retentive timer and preset separated by a space for example “H ST1 K50”.

  • H indicates the high-speed timer

  • ST1 is a retentive timer number.

  • K50 timer preset value.

image

Retentive timer:

  • The retentive timer starts rising when the input of the retentive timer is set to true.

  • The retentive timer goes time out when the preset value becomes equal to the current value.

  • If the input of the retentive timer is turned off during that increment, the coil is de-energized but the current value is stored.

  • To restart again, turn input conditions on again to re-energize the coil.

What is the counter in PLC?

  • The counters allow the number of occurrences of input signals to be counted. A counter is a function block that counts up or counts down until it reaches a preset limit. When the limit is reached the counter output is set.

  • The counter address is C0 to C255

  • For Counter: Preset is the number of Counts.

  • Counter Done Bit: CX

Where X is the address of the counter used.

What are the main types of counters in PLC?

A counter instruction has two basic types

Up counters:

The up counter (CTU) counts up from zero to a preset value. It means the events are added to the set number until it reaches the preset value its contacts change its state from 0 to 1 or vice versa.

Down counters

The down counters (CTD) count down from preset value to zero. It means the events are subtracted from the set value when the counter reaches the zero value its contacts change its state from 0 to 1 or vice versa.

Counter instruction Parameter:

  • Counter number: it is an identification number to declare the counter like C0, C1 up to C234.

  • The Counters in PLC can be defined by addressing C0 K10

Where

C0 is the counter number (0, 1, 2, 3, and 234)

K10 Preset value is the number of Counts to be counted.

  • In this example, C0 is the counter number and K10 is the count preset value. In the nextrung, the timer address is used as ‘NO’ contact. If the input of X0 transitions from LOW to HIGH then the counter counts, like this the counter keeps on counting for each transitions for a defined preset value, when the counter reaches a preset value then output is set to true otherwise false.

image

What does a PLC counter count?

A counter instruction in a PLC programming that either increment (counts up) or decrements (counts down) an integer number value when prompted by the transition of a bit from 0 to 1 (“false” to “true”)

How to reset the counter on a Mitsubishi PLC?

The counter can be reset using RST C instruction to clear the count value and turn off the contact.

When the counter is reset by the RST instruction the present value and contact of the counter are cleared at execution of the RST instruction

What communication protocol is used by Mitsubishi PLC?

  • The Mitsubishi PLC uses the MelsecNet protocol for data transmission; it was developed by Mitsubishi electric.

  • MelsecNet protocol has two types

  • MELSECNET/H: it can transmit a maximum of 19,200 bytes/frame with the speed of 25 Mbit/s

  • MELSECNET/10: it can transmit a maximum of 960 bytes/frame with the speed of 10 Mbit/s

  • Both use coaxial bus type and optical loop type for data transmission. The coaxial bus type uses the token bus method with a distance of 500 meters. But optical loop type uses the token ring method with a distance of 30 kilometres

What are the Features of MelsecNet?

The features of MelsecNet are:

  • It supports 239 networks.

  • Connection between PC, HMI, and PLC Easy

  • High-speed data communications with large data volumes

  • Reliable and robust data transfers

  • Redundancy functions

  • Maximum network distance 30 km, with 255 segments

  • Simple configuration,

  • Remote programming

What is the memory address in Mitsubishi PLC?

The memory addresses used in Mitsubishi PLC are M0 to M3071.

It uses a 3072 memory address.

Which programming software is used for Mitsubishi PLC Programming?

GX-Developer is the programming software used by Mitsubishi PLC.