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: