Belimo 22MT-525 : Active Averaging Duct Temperature Sensor, Continuous Pt1000 1/3 DIN, 20 ft (6 m) Probe, 8 Jumper-Selectable Ranges, 0-5V / 0-10V Output, 1/2" NPT Conduit, NEMA 4X / IP65, 24 VAC/VDC, 5-Year Warranty

What does the 22MT-525 measure and output?

It measures the average temperature of duct air across the full 20 ft (6 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 0-5V / 0-10V active (jumper-selectable).

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 20 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 20 ft probe, a typical duct face of 4×6 ft would accommodate ~3-4 serpentine passes.

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 20 ft variant with 0–5V / 0–10V 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 VAC or 24 VDC supported. Power consumption is 0.8 VA AC / 0.4 W DC — very low draw, compatible with standard 24V control transformers shared with actuators and other sensors.