LG LS Programmable Logic Controller K7M-DR30U K7MDR30U K7M-DR3OU

LS Electric K7M-DR30U | MASTER-K K120S Compact PLC — 18 DI (24VDC) / 12 Relay Outputs / 2A per Contact / RS-232C / Expandable

18 Inputs, 12 Relay Outputs — The K120S in Practice

The K7M-DR30U is a 30-point compact PLC in LS Electric's MASTER-K K120S family. Eighteen 24VDC digital inputs and 12 relay outputs in a single stand-alone body — no rack, no separate power supply, no backplane bus. It is a self-contained controller for machine-level tasks where the I/O count fits within one unit.

The DC input section accepts 24V field signals across a practical supply range (20.4–28.8VDC), covering tolerance variations from the panel's 24VDC supply without input filtering issues. This range matches standard industrial sensors — proximity switches, photoelectric cells, limit switches, and pushbuttons all connect directly.

The 12 relay outputs carry a 2A per contact rating at both DC 24V and AC 220V. This single rating covers most machine output loads: standard motor contactor coils (AC 220V, 50–200mA), 24VDC solenoid valve pilots (100–300mA), and signal lamps at either voltage — all from the same module without interposing relays for voltage conversion. The maximum switching voltage of AC 250V / DC 110V provides headroom for panels with 240VAC or 110VDC control circuits.

Key Specifications

MASTER-K K120S — Where the K7M-DR30U Sits

LS Electric's MASTER-K family spans a range of stand-alone PLC sizes. The K120S sub-series covers the 30-point I/O class — the K7M-DR30U being its relay-output variant. Larger K120S variants extend to 60-point and higher I/O counts in the same family architecture; smaller MASTER-K models (K10S, K30S) cover lower I/O counts.

The K120S supports expansion via additional I/O modules on the right-side expansion bus, allowing the 30-point base unit to grow when the application demands more field connections than the base hardware provides.

Application Scenarios

Small machine tools and OEM equipment: 18 sensor inputs monitor workpiece presence, spindle status, and door interlocks. 12 relay outputs control cooling pump starters, clamp solenoids, and indicator lamps. The standalone controller mounts in the machine's electrical box without rack infrastructure.

Conveyor and sorting panels: Photocell and proximity sensor inputs; motor contactor and diverter relay outputs. Mixed AC and DC loads switch from the same relay output section.

Maintenance spare for MASTER-K installations: The K7M-DR30U remains in service in many Asian, European, and South American industrial installations. A same-model replacement preserves the original terminal assignments, I/O addressing, and ladder programme without modification.

FAQ

Q1: What programming software is used for the K7M-DR30U?

KGL Win — LS Electric's dedicated MASTER-K programming environment. It provides ladder logic (LD), function block diagram (FBD), and instruction list (IL) programming. Connection uses the RS-232C port on the CPU front with a compatible USB-to-RS-232 adapter and PC cable. KGL Win version must be compatible with the K120S CPU firmware.

Q2: What is the difference between K7M-DR30U and K7M-DT30U?

The K7M-DR30U has relay (R) outputs — electromechanical contacts switching AC or DC loads at 2A per contact. The K7M-DT30U has transistor (T) outputs — solid-state 24VDC output. Relay contacts handle mixed AC/DC loads and provide galvanic isolation; transistor outputs switch only DC, faster and without contact wear. Choose relay for AC loads or infrequent-cycle DC loads; choose transistor for high-speed 24VDC switching.

Q3: Can the K7M-DR30U expand beyond 30 I/O points?

Yes. LS Electric provides expansion modules for the MASTER-K K120S series — digital input, digital output, and analogue I/O expansion units connect via the right-side expansion connector. The maximum total I/O in an expanded K120S configuration depends on the CPU model's expansion capacity; confirm from the K120S hardware manual for the specific expansion module count and type limitations.

Q4: What relay protection is recommended for inductive DC loads?

DC inductive loads — relay coils, solenoid valves, and similar devices — generate a reverse voltage spike when switched off. This spike arcs across the relay contact surfaces, eroding them and shortening contact life. Connect a freewheeling diode across each DC inductive load (cathode toward the positive supply rail) to absorb the spike. For AC inductive loads, an RC snubber across the load reduces arcing at both make and break.

Q5: Where is the K7M-DR30U sourced?

Through LS Electric authorised distributors (for current or recently produced units) and through the MASTER-K aftermarket — industrial automation spare parts dealers and surplus suppliers. The MASTER-K family has a substantial installed base in manufacturing and utility applications globally; aftermarket availability is generally good for the 30-point K120S class.