Belimo 22MT-544 : Active Averaging Duct Temperature Sensor, Continuous Pt1000 1/3 DIN, 10 ft (3 m) Probe, 8 Jumper-Selectable Ranges, 4–20 mA Output, 1/2" NPT Conduit, NEMA 4X / IP65, 24 VDC, 5-Year Warranty

What does the 22MT-544 measure and output?

It measures the average temperature of duct air across the full 10 ft (3 m) probe length. Unlike single-point duct sensors, the continuous Pt1000 sensing element integrates temperature along the entire probe path — giving a true bulk-air temperature reading instead of whatever temperature happens to be at one specific point. Output is 4-20 mA active.

Why use an averaging probe instead of a single-point sensor?

Large ducts often have significant air stratification — outdoor air and return air mix imperfectly at AHU mixing dampers, supply air can have hot and cold streaks from imperfect coil contact, and exhaust ducts can have different temperatures depending on which zones are exhausting at any moment. A single-point sensor reads whatever is at its tip, which can be 10°F or more off from the actual bulk-air temperature the BAS needs to control to. An averaging probe integrates across the whole cross-section, giving a representative reading that drives controller logic correctly.

How do I install a 10 ft averaging probe in a duct?

The probe is flexible and installed in a serpentine pattern across the duct cross-section — typically 1-2 ft spacing between curves, covering as much of the duct face area as possible. Use installer-supplied probe-mounting clips or capillary tube supports (Belimo offers compatible accessories) to hold the serpentine shape against duct vibration. The housing mounts on the duct exterior; the probe penetrates the duct wall through a sealed gland. For a 10 ft probe, a typical duct face of 4×6 ft would accommodate ~3-4 serpentine passes.

Why a 4-20 mA output instead of 0-10V?

4-20 mA current loops are immune to voltage drop on long cable runs and have built-in fault detection: 0 mA = broken loop, vs 0V on a voltage output which could mean either zero reading OR broken wiring. Useful for duct-mount sensors far from the BAS panel (AHU plenums, rooftop AHUs). The trade-off: the 4-20 mA variant requires DC supply only (13.5-26.4 VDC); the 0-5V/0-10V variants accept both AC and DC.

How is this different from other 22MT lengths?

The 22MT family covers three probe lengths: 10 ft (3 m) for typical AHU mixed-air, 20 ft (6 m) for larger AHU plenums and mid-size duct cross-sections, and 50 ft (15 m) for very large duct systems and central plant air handlers. Each length is available with V output (22MT-524/525/528) or 4-20 mA output (22MT-544/545/548). Choose by your duct face area and desired serpentine coverage. This SKU is the 10 ft variant with 4–20 mA output.

Where should I install the housing?

On the duct exterior — typically the side or top of the duct, accessible for service. NEMA 4X / IP65 rated for the duct-exterior environment, which often has condensation, washdown exposure, and high ambient humidity. The probe extends through a sealed duct-wall penetration into the airstream. Avoid mounting the housing where it could be damaged by maintenance traffic or where conduit access would be difficult.

How do I configure the 8 measuring ranges?

The active measuring range is set via an on-board jumper (settings S0-S7). Open the housing, locate the range-select jumper, move it to the desired position, and close the housing. The factory default is S2 for outdoor air (22UT) or S4 for typical HVAC duct applications (22MT). Choose the narrowest range that covers your expected operating point — narrower ranges give higher analog resolution. For example, 0-10V mapped across 50-95°F gives ~0.2V per °F, vs ~0.05V per °F for the same output mapped across -30 to 250°F. The narrower range gives 4× the resolution at the BAS input.

Does it need 24V power?

Yes — 24 VDC only (DC 13.5-26.4V for 22UT, DC 15-35V for 22MT). 4-20 mA loop is current-driven so DC supply is required; AC will not power the loop correctly. Power consumption 0.5 W including the loop drive current.