Hotel RCU quotes arrive stuffed with acronyms — RCU, GRMS, PMS, KNX, DND/MUR, card power. This glossary explains the 20 terms buyers meet most so you can compare proposals and read a BOM without guesswork.
Core control terms: RCU, GRMS, PMS
RCU (Room Control Unit) is the embedded controller behind each guest room — it drives lighting, HVAC, curtains and service logic. GRMS (Guest Room Management System) aggregates every RCU to one operations console for status, energy and service calls. PMS (Property Management System) is the hotel's booking and front-desk system; GRMS talks to it over TCP/IP so check-in and check-out flow into room scenes.
Status and service terms: DND, MUR, room status
DND (Do Not Disturb) tells staff to skip the room; MUR (Make Up Room) requests cleaning. Both surface on the GRMS board and can drive the door sign. Room status — rented, vacant, checked-out, inspected — is the single variable that triggers energy and cleaning workflows.
Bus and protocol terms: KNX, RS-485, BLE Mesh, Zigbee, PLC
| Term | One-line meaning |
|---|---|
| KNX | International wired bus standard; best for new-build, long-life installs |
| RS-485 / Modbus | Cheap, robust twisted-pair bus; the budget wired workhorse |
| BLE Mesh | Bluetooth Mesh wireless; self-healing, ideal for retrofit |
| Zigbee | Wireless mesh alternative; needs a coordinator |
| PLC | Power-line carrier; rides existing mains, less common in rooms |
Power and load terms: card power, relay, SCR dimming
Card power (input-card power) cuts room loads when the key card is removed. A relay switches a 230 V load on or off; a contactor handles higher currents. SCR / thyristor dimming (silicon-controlled rectifier) phase-controls lamps for smooth, flicker-free scenes. Match the actuator rating to the load — a dimmer is not a relay.
How to ask the right questions when buying
When you request a quote, ask for: protocol (KNX, RS-485 or BLE Mesh), per-room relay and dimming channel count, PMS interface, certifications, and whether scenes are stored locally or only in the cloud. Those five answers separate a real RCU spec from a box of switches.
Frequently asked questions
- What is the difference between an RCU and a PLC?
- An RCU is purpose-built for guest rooms — scenes, card power, DND/MUR, PMS links — while a PLC is a general industrial controller. For hotels the RCU saves integration effort and matches room workflows out of the box.
- Is a GRMS always necessary?
- For small properties a standalone RCU may suffice, but mid-size and large hotels benefit from a GRMS: one board for room status, energy and service calls instead of walking floors.