Mitsubishi FX PLC NZ | FX3U FX2N FX3G Modules Memory Cassettes

Mitsubishi MELSEC FX Series

Mitsubishi / MELSEC FX series

FX3U-4AD and FX3U-4AD-ADP are different parts. Same function, four analogue inputs, and one mounts on the right of the PLC while the other mounts on the left. The ADP suffix is not a variant, it is the mounting position.

FX is the Mitsubishi compact PLC family and it is on a great deal of imported machinery in New Zealand. FX2N and FX3U are the ones we see most.

Three ways to expand an FX3U

The structural point that explains most FX ordering confusion.

Type	Mounts	Suffix
Expansion board	Inside the main unit	-BD
Special adapter	Left side	-ADP
Special function block	Right side	None

Why it matters

The same function exists in more than one form.

Part	Function	Position
FX3U-4AD	4 analogue inputs	Right side block
FX3U-4AD-ADP	4 analogue inputs	Left side adapter

They are not interchangeable. A panel built around a left-side adapter has no room on the right, and the addressing differs.

So when quoting, check whether the existing module sits to the left or the right of the main unit. A photo settles it instantly.

The BD board

An expansion board fits inside the main unit itself. FX3U-232-BD, FX3U-485-BD, FX3U-USB-BD and FX3U-422-BD are the common ones.

Only one board fits at a time. So a machine with an FX3U-485-BD already fitted cannot also take a USB board without giving one up.

That is often why a communication function was done with an ADP adapter instead.

FX3U takes FX2N modules

The most commercially useful fact about this family.

Mitsubishi states that FX3U CPUs are compatible with existing FX2N expansion modules as well as the FX3U ADP range, and that an FX3U may be used as a replacement for an FX2N PLC.

Scenario	Outcome
FX2N main unit failed, modules good	An FX3U main unit takes the existing FX2N modules
FX2N module failed	Replace like for like, or use the FX3U equivalent

So an obsolete FX2N system is not a full replacement job. The main unit can be brought forward a generation while the analogue, temperature and communication modules stay.

That is worth raising before anyone quotes a rebuild. We can supply either route.

The memory cassette holds the program

The thing that makes an FX3U replacement quick, and most sites do not use it.

When a memory cassette is installed, the cassette's internal program is used in place of the internal RAM memory.

Cassette	Capacity
FX3U-FLROM-16	16 kB
FX3U-FLROM-64	64 kB
FX3U-FLROM-64L	64 kB, with program transfer buttons
FX3U-FLROM-1M	1 MB

Two consequences

A failed main unit with a cassette is a swap. Move the cassette across and the machine runs the same program, with no laptop and no software.

And a machine with a cassette does not lose its program when the battery dies. The program is in flash, not battery-backed RAM.

Same principle as the SICK Flexi Soft system plug covered on our Flexi Soft page.

The 64L is worth knowing about

The FX3U-FLROM-64L has program transfer buttons, allowing permanent overwriting of the RAM-based program.

So you can copy a program between PLCs with the buttons on the cassette, no PC and no software licence required.

On a site with several identical machines, or where nobody has GX Developer, that is genuinely useful.

The battery, and when you need it

The FX3U-32BL battery buffers the internal RAM memory in the event of a power supply failure.

Setup	Battery matters
Program in internal RAM	Critically. A flat battery loses the program
Program in a memory cassette	Less so. The program is in flash

A battery warning on an FX with no memory cassette is urgent. If it goes flat and the power drops, the program is gone and someone needs a backup and the software to reload it.

Batteries are a consumable and cheap. Order them before the warning becomes a problem.

Reading a special function module number

The naming is systematic. The number is channels and the letters are the function.

Code	Function
AD	Analogue input, A to D
DA	Analogue output, D to A
AD-PT	Platinum RTD temperature
AD-TC	Thermocouple
LC	Temperature loop control
HC	High speed counter
PG	Pulse generator, positioning
SSC	SSCNET positioning
CCL	CC-Link
DP	PROFIBUS DP
ENET	Ethernet
232IF, 485	Serial interface

Master and slave differ by suffix

Module	Role
FX3U-16CCL-M	CC-Link master
FX3U-64CCL	CC-Link slave
FX3U-64DP-M	PROFIBUS DP master
FX3U-32DP	PROFIBUS DP slave

The trailing M is master. A master and a slave are not substitutes for each other, and the difference is one character.

Temperature modules are sensor-specific

An AD-PT reads platinum RTDs and an AD-TC reads thermocouples. They are different measurement principles and not interchangeable.

Check what the sensor is before ordering the module.

The common modules

Category	Modules
Analogue input	FX3U-4AD, FX2N-4AD, FX2N-2AD, FX2N-8AD, FX3UC-4AD
Analogue output	FX3U-4DA, FX2N-4DA, FX2N-2DA, FX2NC-4DA
Mixed analogue	FX2N-5A
Temperature	FX3U-4LC, FX2N-2LC, FX2N-4AD-PT, FX2N-4AD-TC
High speed counter	FX3U-2HC, FX2N-1HC, FX2NC-1HC
Positioning	FX3U-1PG, FX2N-10PG, FX3U-20SSC-H
Network	FX3U-16CCL-M, FX3U-64CCL, FX2N-32CCL, FX3U-64DP-M, FX3U-32DP, FX2N-16LNK-M
Serial	FX2N-232IF

The special adapters

Adapter	Function
FX3U-4AD-ADP	4 analogue inputs
FX3U-4DA-ADP	4 analogue outputs
FX3U-3A-ADP	Mixed analogue
FX3U-4AD-PT-ADP, FX3U-4AD-PTW-ADP	Platinum RTD
FX3U-4AD-TC-ADP	Thermocouple
FX3U-4AD-PNK-ADP	Other sensor types
FX3U-ENET-ADP	Ethernet
FX3U-232ADP-MB, FX3U-485ADP-MB	Serial with Modbus

The FX3U-ENET-ADP is how an older FX gets onto Ethernet. Worth knowing if a plant wants to network a machine that currently has none.

The extension power supply

The same budget issue as every modular I/O system.

The FX3U-1PSU-5V is an extension power supply unit. It exists because a long chain of extension blocks can exceed what the main unit supplies.

The symptom of running short is misleading: modules at the far end behave erratically or fail to be recognised, which looks like a faulty module.

If a station has recently been extended and the last modules are misbehaving, check the supply before ordering a replacement.

Programming interfaces

Part	Function
FX-USB-AW	USB to RS422. Programs an FX from a PC USB port
FX-232AWC-H	RS232 converter
FX3U-USB-BD	USB board fitted inside the main unit

The FX-USB-AW is the one most sites need and do not have. An FX programming port is RS422, and no modern laptop has one.

Worth having on the shelf alongside the spares. It costs very little and without it nobody can read the program off a failing PLC.

Cables and connectors

Part	Function
FX0N-30EC, FX0N-65EC	Extension cables, 30 cm and 65 cm
FX2N-CNV-BC	PLC bus connector, needed with an extension cable
FX-16E-150CAB, -300CAB, -500CAB	I/O cables at 1.5 m, 3 m and 5 m
FX-16E-TB/UL	Terminal block
FX2C-I/O-CON series	Connector parts

An extension cable needs the bus connector as well. Ordering the cable alone leaves the job half done.

Display modules

The FX3U-7DM display module, with the FX3U-7DM-HLD holder, gives a small local display on the PLC itself.

Useful where there is no HMI, for monitoring and adjusting values at the panel.

FX3UC is a different physical range

Worth flagging because the numbering looks similar.

FX3UC main units cover 16 to 96 I/O and use connector-type wiring rather than screw terminals. Examples include FX3UC-16MT/D, FX3UC-16MT/DSS and FX3UC-32MT/D.

They are physically and electrically different from an FX3U. A C in the series name means the compact connector range, and the wiring is not compatible.

What to send us

The full model number. Including the ADP or BD suffix if there is one.

Whether the module sits left or right of the main unit. That decides adapter or block.

Whether the main unit has a memory cassette.

What is already fitted, if you are adding.

A photo of the whole assembly. Mitsubishi labels are on the front and one photo usually identifies everything.

What we can supply

Current production. FX5U and FX5UC main units and modules, plus the FX5-CNV-BUS converter for existing FX3 modules. Quoted with a delivered lead time.

Discontinued. FX3U, FX3UC, FX3G, FX2N, FX2NC, FX1N, FX1S and FX0N main units and their full module ranges. Surplus and tested used, which keeps an existing machine on its original program.

Accessories. Memory cassettes, batteries, FX-USB-AW programming interfaces, extension cables, bus connectors, terminal blocks and display modules.

A sensible FX spares holding

For a site running FX, three things cover most eventualities cheaply.

Item	Why
Batteries	Consumable, and losing one loses the program
An FX-USB-AW	Without it nobody can read or load a program
A memory cassette per machine	Turns a PLC failure into a swap

The cassette is the one worth doing now. Fitting one to a running machine takes minutes and removes both the battery risk and the commissioning burden on a future failure.

We buy Mitsubishi FX

FX2N and FX3U main units and modules hold real value, because a like-for-like replacement avoids a program conversion.

If you are stripping a machine, keep the main unit with its modules and its memory cassette. See Sell To Us.

Send us your part numbers

Tell us whether the module sits left or right of the main unit. FX3U-4AD and FX3U-4AD-ADP are different parts. Quotes in NZD including GST.

Request a quote

Industech is an independent supplier of new, surplus and used industrial automation equipment. We are not an authorised distributor of, approved by, sanctioned by, or affiliated with Mitsubishi Electric. MELSEC, CC-Link, SSCNET, GX Developer and GX Works are trademarks of Mitsubishi Electric Corporation. All trademarks, brand names and part numbers are the property of their respective owners and are used here for identification purposes only.