OMRON NX series system unit power configuration and troubleshooting

3.3 Capacity Calculation Example

On site engineers need to calculate the total current consumption of the I/O power supply to ensure the selection of the correct additional I/O power supply unit. The typical formula is as follows:

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Total current consumption of I/O power supply=∑ (I/O power consumption of each unit)

Among them, the I/O power consumption of each unit includes:

Internal I/O power consumption of the unit (e.g. NX-PF0730 consumes 10mA)

Input current of I/O unit (per point x number of points simultaneously turned on)

Current of external sensors/loads

Calculation example: Configure an NX-PF0730 (10mA)+NX-ID3317 input unit (4-point ON, input current 6mA per point, external sensor 50mA per point)+NX-OD3121 output unit (4-point ON, load 125mA per point, output unit consumes 50mA per point). The total current is 10mA+(0+6 × 4+50 × 4) mA+(10+125 × 4+50 × 4) mA=10+224+710=944mA, which is much smaller than 10A capacity, but if using NX1P2 CPU, it cannot exceed 4A.

3.4 Precautions for Inrush Current

When connecting inductive or capacitive loads, the additional I/O power supply unit will experience higher surge currents. It must be ensured that the effective value (Irms) of the current does not exceed the rated value of the unit and related protective devices. Calculation formula:

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Irms = √( Ip² × D + Ia² × (1 - D) )

Where Ip is the peak impulse current, D is the duty cycle (pulse width/period), and Ia is the steady-state current. For NX-PF0730, the maximum allowable peak impulse current is 50A (pulse width of 1s), and when connected to NX1P2, it is 20A.

I/O power connection unit and shielding connection unit: wiring details

4.1 I/O Power Connection Unit (NX-PC00 □□)

This type of unit does not connect to the NX bus for power supply, nor does it generate power. It only provides additional terminals for distributing I/O power. There are three models in total:

NX-PC0020:16 IOV terminals (positive pole of I/O power supply)

NX-PC0010:16 IOG terminals (I/O power negative or COM terminal)

NX-PC0030: 8 IOV+8 IOG terminals

When providing 24V+and 24V - for a large number of three wire sensors or loads, using these units can avoid repeated wiring on each I/O unit. For example, connect the IOV terminal of NX-PC0020 to an external 24V power supply, and then extract multiple+24V from its terminals to multiple sensors, while using NX-PC0010 to provide a common 0V.

Wiring example: For NPN input units (such as NX-ID5342), it is necessary to connect the 0V line of the sensor to IOG and the+24V line to IOV. The use of I/O power connection units can simplify this centralized power distribution.

4.2 Shielded Connection Unit (NX-TBX01)

In industrial sites, shielded cables are usually used to suppress electromagnetic interference when connecting incremental encoders, analog sensors, or communication cables. NX-TBX01 provides 14 SHLD terminals and two functional grounding terminals. Just connect all shielded wires that need to be grounded to the SHLD terminal, and then connect the functional grounding terminal to the grounding copper bar of the control cabinet through a wire (grounding resistance ≤ 100 Ω). This ensures reliable grounding of the shielding layer and avoids the tedious work of making separate grounding clamps for each shielding wire.

Connection topology: encoder cable shielding layer → SHLD terminal → internal connectivity of the unit → functional grounding terminal → cabinet grounding.

Screw free clamping terminal wiring technique

The NX series system units all use Screwless Clamping Terminal Blocks, which do not require a screwdriver to tighten and can be simply inserted. But there are some key points in the wiring process, which often lead to on-site faults.

5.1 Applicable Wires and Terminals

Ferrule copper wire with sleeve: recommended for use. Insert the stripped multi strand wire into the sleeve, press it tightly with specialized crimping pliers, and then directly insert it into the terminal hole. No need to operate the release hole. Applicable sleeves include Phoenix Contact's AI series (0.34-2.5 mm ²) or Weidm ü ller's H series.

Multi strand bare wire: can be directly inserted, but only suitable for currents of 2A and below. If the current is greater than 2A, tin plated multi strand wire or conduit must be used.

Single stranded hard wire: It can also be directly inserted, but the grounding terminal (functional grounding) only allows the use of multiple stranded wires and cannot use single stranded hard wires.

5.2 Wire stripping length

The stripping length of all terminals (except for the grounding terminal) should be 8-10mm; the stripping length of the grounding terminal should be 9-10mm (because the grounding terminal hole is deeper). After stripping, the conductor part should not be scattered or bent.

5.3 Wiring operation steps (for multi stranded bare wires)

Insert a flat screwdriver (recommended Phoenix Contact SZF 0-0, 4X2.5) into the release hole on the side of the terminal at an angle of 10 °~15 ° until you feel the resistance of the spring.

Keep the screwdriver pressed in while fully inserting the prepared wire into the terminal hole.

Pull out the screwdriver, and the spring will automatically clamp the wire.