ABB AC500 PLC Module Wiring Guide

ABB AC500 PLC Module Wiring Guide

System Overview and Basic Principles

The AC500 series PLC system has a high degree of modularity, supporting the expansion of digital, analog, hybrid modules, and multiple bus interface modules. Before building the system, it is necessary to confirm that all component devices meet the rated values and safety requirements, and are operated by qualified professionals. During the wiring and installation process, it is necessary to focus on interference suppression, wiring specifications, and grounding system design, which are the foundation for ensuring the stable operation of the system.

1.1 Interference Sources and Handling Measures

In industrial sites, interference mainly comes from the following aspects:

Strong electrical interference: PLC signals belong to the weak electrical category and are susceptible to strong electrical interference. When wiring, it should be ensured that communication lines, signal lines, and strong current cables are kept at least 20cm away. Weak current cables in cable trenches should be laid below strong current cables.

Interference inside the cabinet: PLC should not be installed in the same cabinet as high-voltage electrical appliances and should be kept away from power lines (spacing>200mm). Inductive loads inside the cabinet (such as relays and contactor coils) need to be connected in parallel with RC arc suppression circuits.

Signal line interference: including differential mode interference and common mode interference. Shielded twisted pair cables, RC filters, dual integration A/D converters, optoelectronic isolators, single point grounding, and other methods can be used to suppress it.

Inverter interference: It can be addressed by installing isolation transformers, filters, output reactors, and using shielded armored cables (armored layer grounded).

1.2 Cable selection and wiring specifications

Switching signal: Generally, ordinary cables are used, and shielded cables are recommended for long-distance transmission.

Analog and high-speed signals: Shielded cables must be used.

Communication cable: It is recommended to use manufacturer specific cables, and high-quality shielded twisted pair cables can be selected when requirements are not high.

Wiring spacing: The distance between weak current signal lines and strong current cables should not be less than 20cm, and the distance between high voltage and high current cables and signal cables should be greater than 60cm.

1.3 Grounding System Design

Grounding is a key link in suppressing interference and ensuring safety, mainly including:

Safe grounding (power grounding): Connect the grounding terminal of the power cord to the cabinet to prevent electrical leakage hazards.

System grounding (main grounding): PLC and controlled equipment are grounded together, with a grounding resistance of ≤ 4 Ω. It is recommended to use independent grounding to avoid common grounding with power equipment.

Signal and shielding grounding:

The analog signal line needs to be grounded, while the switch signal can be left ungrounded.

The shielding layer should be grounded at a single point (both ends can be grounded in high-frequency situations).

Each node GND for non isolated 485 communication must be grounded, while isolated communication can be grounded at a single point.

Grounding inspection: Interference can be determined by measuring the AC voltage difference between the signal line and ground using a multimeter.

1.4 Differences between Source and Drain Wiring

PNP (source type) sensor: Output high level, current flows from the sensor to the load. Connect the PLC input COM terminal to the negative terminal of the power supply.

NPN (leakage type) sensor: Output low level, current flows from the load to the sensor. Connect the PLC input COM terminal to the positive pole of the power supply.

PLC output module: source type output COM connected to positive pole, drain type output COM connected to negative pole.

Correctly distinguishing and wiring is a prerequisite for avoiding I/O misoperation.

1.5 Wiring System for Analog Signal

Two wire system: The power supply and signal share two wires, suitable for passive sensors.

Three wire system: Short circuit the power supply negative line and the signal negative line, which is actually a variant of the four wire system.

Four wire system: The power supply and signal are completely independent, suitable for active sensors.

Thermistor wiring: Two wire system without compensation, three wire system can eliminate the influence of lead resistance, and four wire system completely eliminates lead resistance, with the highest accuracy.

Detailed explanation of wiring for digital I/O modules

2.1 Switching input module

Taking DI524 (32 channel 24VDC input) as an example:

The module is connected through the TU515/TU516 motherboard terminals, with terminals 1.8-4.8 being UP (+24VDC) and 1.9-4.9 being ZP (0V).

The input can be connected as source or drain type, and attention should be paid to the polarity matching of the common terminal (COM) when wiring.

The module structures of DI561, DI562, DI571, etc. are similar, all supporting source/drain input and obtaining internal power through the I/O bus.