LS PLC XGQ-TR4A Programmable Logic Controller XGT Series Output Module XGQ-TR4A,EXP XGQ-TR4A

LS Electric XGQ-TR4A | 32-Point NPN (Sink) Transistor Output Module — DC 12/24V, 0.1A Per Point, Photocoupler Isolation, ≤1ms Response, XGK PLC Series

Overview

The LS Electric XGQ-TR4A is a 32-point NPN transistor output module for the XGK series programmable logic controller, providing 32 individually controlled open-collector transistor outputs rated at 0.1A each against DC 12V or 24V field supply.

It is the sink-type module in a product family that also includes the source-type equivalent (XGQ-TR4B), and it differs from the lower-density XGQ-TR2A (16-point) and higher-density XGQ-TR8A (64-point) variants in fitting 32 output channels into a single module slot.

NPN transistor output modules are the standard choice for factory automation in regions and industries where DC sink wiring is the predominant convention.

In a sink-type circuit, the module provides the return path to common (0V) for each field device — solenoid valves, indicator lights, motor starter coils driven through relay interfaces, and similar DC-powered loads. 

The field power supply's positive terminal connects to one side of the load; the XGQ-TR4A's transistor connects the other side to common when the output is commanded ON, completing the circuit and energising the load.

Photocoupler isolation between the PLC's logic side and the field output circuit is standard on the XGQ-TR4A. Each output channel passes through an optical isolator that electrically separates the PLC's internal 5V logic bus from the 12V or 24V field wiring.

This isolation prevents field-side voltage transients, wiring errors, or short-circuit currents from reaching the PLC's backplane — important protection in real-world installations where wiring mistakes during commissioning or maintenance can put field voltage directly on a module terminal.

At 0.1A per point with a 2A common limit, the XGQ-TR4A is sized for control-class loads: solenoid coils through relay interfaces, digital input modules on remote I/O systems, LED indicators, small signal relays, and similar loads well within the 0.1A continuous current capability.

Direct drive of power loads above 0.1A requires interposing relays or solid-state relay modules between the XGQ-TR4A outputs and the load.

Key Specifications

NPN vs PNP — Why It Matters for Wiring

The XGQ-TR4A is the NPN (sink) version of the 32-point transistor output module; its PNP (source) counterpart is the XGQ-TR4B. The distinction is fundamental to field wiring compatibility.

NPN outputs provide the low-side switch for each output circuit: the field device's positive supply connects directly to the load, and the module's transistor connects the load's return to the module's COM terminal when active. 

PNP outputs provide the high-side switch: the COM terminal carries the positive supply, and the transistor connects the positive supply to the load when active.

The choice between NPN and PNP is determined by the field devices being controlled and the electrical conventions used in the machine's wiring design.

If the control devices in the system (solenoid valves, indicator lamps, relay coils) have one terminal wired to the 24V positive bus and require a switched return path to 0V, NPN (sink) is the correct module.

If the devices are wired with 0V connected and require a switched 24V supply, PNP (source) is correct.

Mixing NPN and PNP module types in the same system is possible — different modules in different slots — but each must match the wiring convention of its own output group.

Common Current Limit — Practical Implication

The 2A common limit means that while each individual output can sink 0.1A, the sum of all simultaneously active outputs cannot exceed 2A. With 32 points at 0.1A each, the theoretical maximum simultaneous current is 3.2A — exceeding the 2A common limit.

In practice, this limits the number of outputs that can be simultaneously ON to 20 points at maximum load (20 × 0.1A = 2.0A).

If the application's load profile requires more than 20 simultaneous active outputs at full current, the load per point must be reduced proportionally, or the application should be reviewed for module sizing.

For many real-world control applications, this constraint is not binding: solenoid coils and relay coils that comprise the typical XGQ-TR4A load often draw 50mA or less, which means 32 simultaneous outputs at 50mA totals only 1.6A — well within the 2A common limit.

The 40-Pin Connector and Wiring Accessories

The XGQ-TR4A uses a 40-pin connector for all 32 output channels and the common terminals.

LS Electric specifies Smart Link terminal boards and cables for field wiring: the C40HF-xx cable series (in lengths of 0.5m, 1.0m, 1.5m, 2.0m, and 3.0m) connects the module's 40-pin connector to relay terminal boards (R32C-NS5A-40P) or standard terminal blocks (TG7-1H40S, TG7-1H40CA). 

These accessories simplify field wiring by replacing individual conductor connections at the module with a single multi-way cable to a field-side terminal board where individual conductor terminations are made.

Discontinued Status and Sourcing

The XGQ-TR4A was discontinued by LS Electric as part of the product family transition. Machines and systems built with XGK-series PLCs that include XGQ-TR4A modules will continue to need replacement modules as long as the equipment is in service.

The aftermarket carries both new-old-stock units and refurbished/tested units from decommissioned equipment.

When sourcing a replacement, confirm that the module is tested with known-good firmware and outputs verified operational, as untested surplus units may carry latent faults from their previous installations.

FAQ

Q1: The XGQ-TR4A is discontinued. What is the current LS Electric equivalent for a new machine design?

LS Electric's current XGK-compatible output module lineup continues to include transistor output modules in the same physical format.

Consult LS Electric's current XGK series I/O catalog for the replacement designations; the functional specification (32-point NPN transistor, DC 12/24V, 0.1A per point) remains available in the current product range.

For existing machines where the XGK base is unchanged, sourcing surplus or refurbished XGQ-TR4A units is the most straightforward path.

Q2: Can the XGQ-TR4A outputs drive inductive loads directly (solenoid coils), and is any protection required?

Yes, solenoid coils are a typical XGQ-TR4A load, provided the coil's current draw does not exceed 0.1A per point and the simultaneous total does not exceed 2A at the common. Inductive loads generate a back-EMF voltage spike when switched off; this spike must be suppressed by a freewheeling diode connected in parallel with the coil (cathode to positive supply, anode to the switched terminal).

Without freewheeling diodes, the back-EMF spikes degrade transistor life and can produce spurious signals on adjacent wiring.

Most 24V industrial solenoid coils include internal suppression, but this should be verified from the coil's datasheet before relying on it.

Q3: The response time is listed as ≤1ms. What does this mean for time-critical output control applications?

The ≤1ms response time is the transistor switching delay from a command change at the PLC to the corresponding change at the output terminal.

For most industrial control tasks — solenoid valve actuation, conveyor start/stop, indicator control — 1ms is negligible relative to the mechanical response time of the controlled device and the PLC scan cycle time.

For applications requiring microsecond-precision output timing (e.g., stepper motor pulse generation), a transistor output module is not appropriate; a high-speed pulse output module with its own timing hardware is required.

Q4: Can the XGQ-TR4A be used with the XGB compact PLC as well as the XGK modular PLC?

The XGQ-TR4A is an I/O module for the XGK modular PLC system and is not directly compatible with the XGB compact PLC, which uses a different I/O expansion architecture.

The XGB system uses its own expansion I/O modules specific to the XGB bus format. If the existing system is XGK-based, the XGQ-TR4A is the correct module.

For XGB-based systems, consult LS Electric's XGB expansion I/O catalog for the appropriate transistor output module.

Q5: When sourcing a used XGQ-TR4A, what verification tests confirm the module is functional?

A thorough functional test requires mounting the module in an XGK base, powering the system, and commanding each of the 32 output channels ON and OFF through the PLC's diagnostic functions or a test program, while measuring the output terminal voltage with a multimeter or checking it with a test lamp on each channel. Confirm that each channel pulls to near 0V (≤0.2V) when ON and floats to the supply voltage when OFF.

Any channel that fails to switch, remains near 0V when OFF, or exceeds 0.2V when ON has a transistor fault. Additionally, verify the module's status LED behaviour during the test sequence.