OMRON NX series system unit power configuration and troubleshooting

OMRON NX Series System Unit: Complete Guide to Power Architecture and Field Wiring

In industrial automation control systems, OMRON's NX series I/O platform is widely used in various scenarios such as NJ/NX series CPU racks, EtherCAT slave terminal blocks, and safety network controllers due to its modular design and flexible power architecture. Among them, System Units - including Additional NX Unit Power Unit (NX-PD1 □□□□□), Additional I/O Power Unit (NX-PF0 □□□□), I/O Power Connection Unit (NX-PC0 □□□□), and Shielding Connection Unit (NX-TBX01) - are the key to achieving stable distributed power management and reliable signal shielding. This article will provide a complete technical guide for on-site maintenance engineers based on the NX series system unit user manual, covering selection, installation, wiring, and troubleshooting.

Overview of NX Series System Units: Four Core Types and Applications

The NX series system unit is not an I/O module, but a dedicated unit used to build and expand CPU racks or slave terminal power systems. They do not process process data, only manage and distribute power, and provide auxiliary wiring. The four main types of uses are as follows:

Example of Unit Type and Model Main Functions

When the power supply of the NX unit embedded in the CPU or communication coupler is insufficient, an additional NX unit power supply is generated from the external 24VDC power supply to power the NX unit on the right side.

The additional I/O power supply units NX-PF0630 (4A)/NX-PF0730 (10A) provide I/O power supply from the NX bus to the I/O units; Can be used to expand the capacity of I/O power supply or separate I/O power supply segments of different voltage levels.

The I/O power connection units NX-PC0020 (16 × IOV)/NX-PC0010 (16 × IOG)/NX-PC0030 (8 × IOV+8 × IOG) provide additional I/O power terminals (IOV or IOG) for centralized power distribution to external sensors or loads, and do not form power isolation themselves.

The shielded connection unit NX-TBX01 provides 14 SHLD terminals, making it easy to connect multiple shielded wires to the same functional ground.

These system units all adopt a compact design with a width of 12mm, compliant with DIN rail installation, and use Screwless Clamping Terminal Blocks, which can significantly reduce wiring time.

Power architecture: The difference between unit power and I/O power

In the NX series system, there are two fundamentally different power sources:

2.1 Unit Power Supply

Function: To supply power to the internal logic circuits of CPU units, communication couplers, and all NX units.

Generation method: 24VDC is input through the CPU unit, communication coupler, or Unit power supply terminals (UV/UG) of the additional NX unit power supply unit (NX-PD1000). The internal power conversion circuit then generates the voltage required for NX unit operation and transmits it to the NX unit on the right side through the NX bus connector.

Key limitation: The entire CPU rack or slave terminal must use the same unit power supply. If different power sources are mixed, the potential difference may cause abnormal currents and damage the equipment.

2.2 I/O Power Supply

Function: Provide power for on-site signal circuits and external sensors/actuators of NX I/O units (digital input/output, analog input/output, etc.).

Two power supply methods:

Power supply through NX bus: I/O power is input from the I/O power terminal of the communication coupler or additional I/O power supply unit (NX-PF0630/0730), and then transmitted to the right I/O unit through the NX bus connector. This is the most common way.

Individually powered from the outside: Some I/O units have their own I/O power terminals, which can be directly powered by external 24V/5V without relying on the NX bus.

Important principle: The unit power supply and I/O power supply must use independent power supplies (cannot share a 24V power supply), otherwise noise may couple through the power line, causing I/O misoperation.

Additional I/O Power Unit: Solution for Insufficient Capacity

When the built-in I/O power capacity of the communication coupler or CPU unit (usually 4A or less) cannot meet the total current demand of subsequent I/O units, additional I/O power units need to be inserted into the rack. This unit has two main functions:

3.1 Expanding the Capacity of I/O Power Supply

NX-PF0630: Maximum 4A (suitable for most NX1P2 CPU racks, with an upper limit of 4A)

NX-PF0730: Maximum 10A (note: when connected to NX1P2 CPU, the actual maximum is still 4A; when connected to NX502, it can reach 10A)

The additional I/O power supply unit takes power from an external I/O power supply (5~24VDC, voltage needs to match the I/O unit used), and then delivers the I/O power supply to all NX units on its right side through the NX bus. Starting from this unit, the I/O power supply in the right paragraph is based on the input voltage of this unit, thus achieving power segmentation.

3.2 Separate I/O power supply segments (voltage isolation)

If different parts of a system require different I/O power supply voltages (such as 24V input units and 5V output units), or if it is necessary to electrically isolate the I/O power supplies in different areas to avoid interference, an additional I/O power supply unit can be inserted in the middle. The left paragraph uses one type of I/O power supply, while the right paragraph of the unit uses another type of I/O power supply (input through the unit's own I/O power terminal). This makes the power system very flexible.