QX70 is a 16-point 24 V DC digital input module for Mitsubishi Electric’s MELSEC-Q series programmable logic controller platform, providing sink/source selectable inputs with a 5 ms response time for connection to standard pushbuttons, proximity sensors, and discrete field devices. The QX70 occupies a single I/O slot on any Q-series base unit and is compatible with all Q-series CPU types, offering a cost-effective solution for expanding digital input capacity in both new installations and existing Q-series systems. In stock at Atlantech Drives. Request your quote within 24-48 hours with worldwide shipping and 12-month warranty.
What Is the QX70?
The QX70 is a standard-density digital input module in the MELSEC-Q I/O range, providing 16 input points across two 8-point commons in a single slot module body. The «X» designation identifies it as an input module within Mitsubishi’s Q-series naming convention, and «70» places it in the 24 V DC sink/source compatible input family. Unlike the QX40 (which requires sink-only wiring) or the QX80 (32-point higher-density variant), the QX70 supports both NPN (sink) and PNP (source) field wiring without hardware jumper changes — the input common polarity is determined by the external wiring configuration, making the module suitable for mixed-sensor installations and simplifying stock management for maintenance teams who maintain a single input module type across different machine configurations. Each input point is optically isolated from the Q-bus backplane, providing 500 V AC isolation between field wiring and the PLC logic circuits.
Key Technical Specifications
- Number of Input Points: 16
- Input Voltage: 24 V DC (20.4–28.8 V DC operating range)
- Input Current: Approx. 4 mA per point at 24 V DC
- Input Impedance: 5.6 kΩ
- ON Voltage / Current: 19 V DC or more / 3 mA or more
- OFF Voltage / Current: 11 V DC or less / 1.7 mA or less
- Input Response Time: 1 ms / 5 ms / 10 ms / 20 ms / 70 ms (selectable per module)
- Common Configuration: 2 commons (8 points per common)
- Isolation: Photocoupler (500 V AC between field and Q-bus)
- Wiring Type: Sink or Source (determined by external wiring)
- Current Consumption: 5 V DC, 0.10 A (from Q-bus)
- Operating Temperature: 0 °C to 55 °C
- Dimensions (W × H × D): 27.4 × 98 × 90 mm
- Weight: Approx. 100 g
Typical Industrial Applications
The QX70 is one of the most widely stocked Q-series modules in maintenance inventories globally due to its universal sink/source compatibility and moderate I/O density. In automotive assembly plants, QX70 modules are used extensively for limit switch and inductive proximity sensor inputs on body-in-white welding fixtures, where the mixed NPN/PNP sensor population from different sensor manufacturers is accommodated without module variants. In process industries, the QX70’s selectable response time filter (up to 70 ms) allows it to suppress contact bounce from legacy mechanical float switches and pressure switches in tank level monitoring applications without requiring external filter relays. In semiconductor fab equipment, the optical isolation and 500 V AC withstand voltage make the QX70 suitable for I/O points connected to equipment with different ground references — a common condition in wafer handling systems where multiple sub-systems share a common PLC but have isolated power domains. The 5 ms default response time is adequate for the vast majority of discrete I/O applications; for inputs requiring faster response (conveyor speed detection, registration mark sensing), the QX70 should be replaced with a high-speed input module such as the QX40H, or the FX3U-4HSX-ADP adapter for FX3U-based systems.
Installation Advice
The QX70 uses a 40-pin connector (MIL connector, two rows of 20 pins) for field wiring — always use Mitsubishi’s A6CON1 (crimp-type) or A6CON4 (spring-clamp) connector housing rather than generic MIL connectors, as the locking tab geometry differs and generic connectors can vibrate loose in high-vibration environments. Label each connector before removal during module replacement — the 40-pin connector is not keyed against insertion on an adjacent module’s identical connector, and incorrect connector placement is a common wiring error during maintenance. When wiring sink (NPN) sensors, connect the 24 V DC positive to the COM terminal and the sensor NPN output to the input terminal; for source (PNP) sensors, connect 24 V DC negative (0 V) to the COM terminal and the PNP output to the input terminal — do not mix sink and source wiring within the same 8-point common group, as this will create a short circuit through the common terminal. Set the input response time filter to the minimum value that reliably filters the expected contact bounce or signal noise — unnecessary filter delay increases the effective input latency visible to the CPU scan and can cause missed pulses in fast-cycling applications. Verify module seating by checking that the module latch clicks fully into the base unit slot — partially seated modules cause intermittent bus communication errors that are diagnostically misleading because they may appear as CPU errors rather than I/O faults.
Frequently Asked Questions
Q: Can the QX70 be used in a MELSEC-Q remote I/O station on a CC-Link or CC-Link IE network?
A: Yes. The QX70 can be installed in a Q-series remote I/O base unit (such as the QJ61BT11N CC-Link remote station or the QJ71GF11-T2 CC-Link IE Field remote station) and operated as remote discrete input points from a master Q-series CPU. The module’s electrical characteristics are identical in remote operation; only the data refresh timing differs, as remote I/O data is updated at the network scan interval rather than the CPU scan interval.
Q: What is the difference between the QX70 and QX72 input modules?
A: The QX72 is a 16-point input module optimised for 24 V DC inputs with a higher input current per point (approximately 7 mA vs 4 mA for the QX70), making it better suited for field devices with higher minimum load current requirements such as certain two-wire proximity sensors. The QX70’s lower input current is adequate for the majority of modern three-wire sensors and is more economical for high-density installations. Verify the minimum load current specification of your sensor against the QX70’s OFF-state current threshold before selecting the module type.
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