Belimo 22RTM-5900A : Active Room CO2 + Humidity + Temperature Sensor, NDIR Dual-Channel CO2 with Traffic-Light LED, MP-Bus + Analog Output (0-5V / 0-10V / 2-10V), 3 Analog Outputs, NFC Configuration, 24 VAC/VDC, NEMA 1 / IP30, 5-Year Warranty

What does the 22RTM-5900A measure and output?

It measures CO2, relative humidity, and room air temperature, and outputs three analog signals: by default AO1 = temperature, AO2 = setpoint temperature, and AO3 = CO2. The humidity output mapping is configurable via the Belimo Assistant 2 app (most installations re-map AO2 or AO3 to humidity if setpoint adjustment isn't needed). Each output is jumper-selectable via NFC between 0-5V, 0-10V (factory default), and 2-10V to match your BAS controller's input range.

How does the CO2 traffic-light LED work?

The on-housing LED automatically changes color based on CO2 concentration: green (good — typically < 800 ppm), yellow (caution — typically 800-1200 ppm), red (poor — typically > 1200 ppm). Thresholds are user-configurable via the Belimo Assistant 2 app, so you can match the LED to your space's IAQ targets (ASHRAE, LEED, school/healthcare guidelines all differ). The LED can be deactivated entirely if a visual indicator isn't desired — useful in hotel guest rooms or executive offices where a flashing red LED would be unwelcome.

How does NDIR dual-channel CO2 sensing work?

NDIR (non-dispersive infrared) measures CO2 by detecting how much infrared light the gas absorbs at a specific wavelength. The 'dual-channel' design uses a second reference wavelength that CO2 does NOT absorb — by comparing the two signals, the sensor automatically corrects for lamp aging, dirt accumulation on the optics, and background gas interference. This is why the sensor is self-calibrating and rated for ±20 ppm/year long-term stability without manual recalibration. Belimo recommends recalibration only after 5 years of operation, and even then only if the application requires the highest precision.

Does this sensor have a display?

No physical display on the housing — only the CO2 traffic-light LED. The 22RTM-5900A is the display-less variant; occupants and technicians view live CO2, humidity, and temperature values and adjust the setpoint by tapping an NFC-equipped phone with the free Belimo Display App against the housing. If you need an on-wall ePaper touch display, see the 22RTM-5900D variant ($1,059).

How does the setpoint adjustment work without a display or knob?

The occupant downloads the free Belimo Display App (iOS / Android) and taps their phone against the housing — NFC reads the current setpoint, the user adjusts it on the phone, and a second tap writes the new setpoint. The sensor's AO2 output then reflects the new setpoint, which the BAS uses to drive the room's VAV box, fan-coil unit, or terminal HVAC element. Because there's no physical control, occupants can't accidentally bump the setpoint or tamper with the housing — useful in classrooms, conference rooms, and shared tenant spaces.

What is MP-Bus and do I need a Belimo controller to use this sensor?

MP-Bus is Belimo's proprietary single-wire bus for daisy-chaining up to 8 (16) actuators and sensors to a single MP-Bus controller. You do NOT need an MP-Bus controller to use this sensor — the analog outputs work with any third-party BAS. MP-Bus is available as an option for installations that already use Belimo MP-Bus controllers and want to consolidate the sensor onto the existing bus.

How is this different from the 22RT and 22RTH variants?

The 22RT family measures temperature ONLY ($250). The 22RTH family adds humidity (Humidity + Temp, $462). The 22RTM family (this SKU) adds CO2 to both — CO2 + Humidity + Temperature, with the CO2 traffic-light LED ($726). Choose 22RTM when CO2 drives demand-controlled ventilation (DCV) in your space; the LED gives occupants a visual IAQ cue beyond the BAS-driven damper response.

Where can I install this sensor?

Indoor wall mount only — NEMA 1 / IP30 enclosure. Cable entry from back (in-wall conduit), top, or bottom of the housing. Standard thermostat-height wall mount is typical. Mount in the breathing zone (4-6 ft above floor) for representative CO2 and humidity readings; avoid exterior walls (heat loss/gain biases temperature) and corners with poor air circulation (CO2 readings lag actual room conditions). Avoid mounting near return-air grilles where CO2 will read lower than occupant breathing-zone levels.

Does it need 24V power?

Yes. The 22RTM-5900A requires 24 VAC or 24 VDC (19.2-28.8V either way). Power consumption is 1 VA AC / 0.5 W DC — very low draw, suitable for sharing a 24V transformer with multiple sensors and small actuators.

Can I configure the sensor without a smartphone?

The factory default settings (0-10V outputs, 32-122°F range, 0-2000 ppm CO2 range, AO1=Temp / AO2=Setpoint / AO3=CO2) work for most installations and don't require any configuration. If you need to change output ranges, remap which value goes to which output, adjust CO2 TLF thresholds, or set MP-Bus parameters, you'll need either: (1) the free Belimo Assistant 2 app on an NFC-capable smartphone, or (2) the LINK.10 Bluetooth/USB-to-NFC dongle on a laptop running Belimo Assistant 2 (useful for desk-side bench commissioning of multiple units).