OMRON NT Series HMI Replacement and Maintenance

OMRON NT Series HMI Replacement and Maintenance

In industrial automation sites, OMRON NT series programmable terminals (PTs) serve various production lines for a long time due to their stable performance and rich communication interfaces. However, with the discontinuation of models such as NT31, NT31C, and NT20 in 2014-2015, a large number of devices still in operation faced practical problems such as spare parts depletion, inability to migrate screen data, and mismatched communication interfaces. How to smoothly replace HMI or extend the service life of existing NT series without stopping production has become a core skill that on-site engineers must master. This article will provide a complete NT series maintenance and replacement guide from five dimensions: model identification, communication protocol selection, screen data backup and conversion, system program upgrade, and common troubleshooting.

Model identification and alternative selection

The NT series covers multiple display sizes and color types, and correctly identifying existing models is the first step in replacement. The common models and key parameters are as follows:

Model Display Type Resolution Effective Display Size Shutdown Time

NT631C-ST153-EV3 TFT color 640 × 480 211 × 158 mm has been discontinued

NT31C-ST143-EV3 STN Color 320 × 240 118 × 89 mm March 2014

NT31-ST123-EV3 STN monochrome 320 × 240 118 × 89 mm March 2014

NT20-ST121-E STN monochrome 256 × 128 115 × 57.6 mm September 2015

Principle of replacement selection:

Display size and resolution: NT631C (10.4 inches) is the preferred alternative for NB series or NA series corresponding sizes; NT31 (5.7 inches) can consider NB5Q or NV5Q.

Communication protocol compatibility: The original NT series supports NT Link (1:1, 1: N, high-speed), Host Link, Memory Link, etc. When replacing, it is necessary to confirm whether the new HMI also supports these protocols or achieves compatibility through a protocol conversion gateway (such as OMRON NS series).

Number of touch switches: NT31 supports a maximum of 192 touch switches of 16 × 12, while NT20 supports 72 touch switches of 12 × 6. The touch resolution of the replacement model should not be lower than the original specifications.

Environmental protection level: The NT series front panel has a protection level of IP65 (oil mist type) and NEMA4. When replacing, products with the same protection level should be selected, especially in situations with cutting fluid and oil mist.

Communication interface and connection method

The communication interface configuration of NT series HMI directly affects the online capability with PLC. Significant differences in interfaces among different models:

NT631C/NT31C/NT31：

Port A: RS-232C (D-sub 9-pin, capable of outputting+5V/250mA)

Port B: RS-232C (can be switched to RS-422A/485 through memory switch)

Printer interface: Centronics parallel port

Expansion I/F: Dedicated connector

NT20：

Port A: RS-232C (9-pin,+5V/150mA)

Port B: RS-232C (9-pin,+5V/150mA, two ports cannot use+5V output simultaneously)

Key Connection Scenarios:

1: 1 NT Link: Suitable for C200HX/HG/HE, CQM1, CPM2A, CVM1/CV series, etc. Just one RS-232C cable (XW2Z-200T/500T) is needed to connect the PLC's peripheral port or RS-232C port to HMI port A. Attention: The direct connection of C200H requires the use of NT20-IF001 adapter.

1: N NT Link (multiple HMIs sharing PLC data): Use RS-422A/485 interface, set port B of NT31/631 to RS-422A mode, and connect up to 32 HMIs (different station numbers need to be set). Recommend using shielded twisted pair cables with terminal resistance ON.

High speed NT Link: For CJ1 and CS1 series PLCs, the response speed is faster and a dedicated NT Link mode needs to be set on the PLC side.

Host Link: Suitable for almost all OMRON PLCs (including C-series, CV series, CJ/CS, etc.). HMI serves as the host link master station, while PLC serves as the slave station, communicating through RS-232C or RS-422A. The maximum baud rate is 19200bps.

Memory Link: Used to connect personal computers or single board computers. As a slave station, HMI allows the upper computer to directly read and write the HMI's memory table through RS-232C. Commonly used for data collection and formula management.

Wiring issues during actual replacement:

The original cable model is XW2Z-200T (9-9-pin, 2-meter) or XW2Z-200S (25-25 pin). If the new HMI ports are different, an adapter cable needs to be made. Be sure to confirm the pin definition: The 6th pin of NT series port A provides+5V power supply (to some PLC programming ports). If the new HMI does not have this output, an additional external power supply is required.

When using RS-422A for long-distance communication (up to 500 meters), the terminal resistance (110 Ω) must be set to ON (via memory switch on NT31/631, not physical DIP).

Screen data backup and migration

The screen data of the NT series is stored in internal flash memory or external Memory Unit (NT-MF261). The data migration after shutdown can be divided into two situations:

3.1 Use Support Tool for Upload/Download

The NT series dedicated Support Tool (NT-ZJCAT1-EV4) supports Windows 98 to Windows 7 (32-bit) and can communicate with HMI through RS-232C cable. Operation steps:

Connect the computer COM port to HMI port A using XW2Z-S002 cable.

Open the Support Tool and select "PT → PC" to upload existing screen data.

Convert data into a format recognizable by new HMIs (such as NB/NA series). OMRON provides the "NT to NB Converter" tool, which can batch convert NT series screen data into NB series projects, but requires manual adjustment of some objects (such as numerical display and charts).

Attention: If the original NT20 uses the Memory Link system program (non-standard Host Link), the Support Tool needs to install the corresponding system program file, otherwise it will not be able to read the screen correctly.

3.2 Directly copy using Memory Unit (NT-MF261)

The Memory Unit can be used for NT631C/NT31/NT20 (universal), and it is an SRAM memory card that requires battery retention. Usage:

On the source HMI, write screen data to the Memory Unit using the Support Tool.

Insert the Memory Unit into the target HMI, and after power on, the HMI will automatically detect and prompt whether to transfer.

After the transmission is completed, the RUN indicator light flashes (normally on).

The battery life of a Memory Unit is about 5 years, and backup units that have not been used for a long time should have their battery voltage checked before replacement.

3.3 Alternative solutions when unable to read raw data

If the original HMI is damaged and there is no backup, the HMI function can only be inferred based on the on-site PLC program. Common practice:

Monitor the DM and CIO areas in the PLC that communicate with the HMI, and record the numerical changes of each address.

Using the online monitoring function of PLC, trigger the touch switches of the original HMI one by one and record the corresponding PLC bit addresses.

Redraw the screen on the new HMI and write macro programs to simulate the original functions.

System program upgrade and compatibility

The system programs (firmware) of the NT series can be updated through the System Installer tool to support new communication protocols or fix defects.

Version correspondence:

NT31/631 system program version 4. x can only use System Installer V2 (included in Support Tool 4.08 and above). The old version of Installer (V1. x) only supports versions 3. x and below.

The NT20 system program requires the use of System Installer V2.1 (Support Tool 4.8 and above).

Upgrading precautions:

Before upgrading, it is necessary to back up the current screen data, as upgrading the system program may clear the user screen.

System programs of different language versions cannot be mixed. For example, Simplified Chinese system programs can only be installed on NT20-ST121 (B) - EC models and require the purchase of a dedicated version.

After upgrading, communication parameters such as port mode and baud rate need to be reset.

Common system program types (taking NT20 as an example):

Standard version: Supports Host Link, NT Link, C200H direct communication.

Memory Link version: Only supports RS-232C Memory Link protocol (for connecting to PC).

Mitsubishi FX Series Special Edition: Directly connected to Mitsubishi FX Series PLC.

If the original NT20 uses the Memory Link system program, the new HMI must also support Memory Link when replacing it (such as NS series or NB series, which need to be simulated through macro instructions), otherwise direct communication cannot be achieved.

Typical troubleshooting and preventive maintenance

5.1 Touch screen unresponsive or triggered incorrectly

Reason: Aging of touch panel, surface oil stains, calibration failure.

handle:

Clean the screen surface with a neutral cleaner (avoid using benzene solvents).

NT31/NT631 supports 100 level contrast adjustment through the touch panel, or you can try entering the system menu to recalibrate the touch position.

If the touch area deviates by more than 5mm, the touch panel needs to be replaced (accessories can be ordered from OMRON).

5.2 Backlight not lit or darkened

Reason: CCFL backlight lifespan is exhausted (nominal 50000 hours, approximately 5.7 years).

handle:

The backlight of NT20 cannot be replaced (with a lifespan of 50000 hours), and the HMI needs to be replaced as a whole.

The backlight of NT31/NT631 can be replaced (requires disassembly). After replacement, the backlight timer (parameter settings) needs to be reset in the Support Tool.

If the backlight becomes dim but still lights up, you can try adjusting the brightness (NT31 supports 3-level brightness adjustment).

5.3 Communication Failure (No Response or Data Error)

Troubleshooting process:

Check if the cable is intact and if the plug screws are tightened.

Confirm that the HMI port mode is consistent with the PLC (RS-232C/422A/485).

Verify communication parameters: baud rate, data bits (7/8), stop bits (1/2), parity (even/odd/none).

For 1: N NT Link, check if the station numbers of each HMI are duplicated (station numbers are set through memory switches).

Check the "Communication Diagnosis" or error log (if any) in the HMI system menu.

5.4 Low battery voltage alarm

NT31/NT631 has a lithium battery (C500-BAT08) inside, which is used to maintain the clock and some memory table data. When the RUN indicator light flashes orange or the screen displays "BAT", the battery needs to be replaced within 30 days, otherwise data may be lost.

Replacement steps:

Turn off the power and open the back battery cover.

Remove the old battery and immediately install the new battery (ensuring correct polarity).

After powering on, enter the system menu and reset the date and time.

5.5 Abnormal or blurred screen display on the screen

Possible reasons:

The contrast setting is incorrect (NT31 can be adjusted through the touch panel, NT20 needs to adjust the potentiometer on the back).

System program damage or version mismatch (requires reinstallation of system program).

Screen data verification error (retransmission of screen data).