Belimo 22MT-545 : Active Flexible Cable Averaging Temperature Transmitter, 4–20 mA (loop-powered), 24 VAC/VDC, 8 Selectable Ranges, 20 ft (6 m) Flex Probe, NEMA 4X / IP65, Mounting Kit Included, 5-Year Warranty

What output signal does the 22MT-545 provide?

4–20 mA (loop-powered), with max. 500 Ω loop resistance. Two-wire 4-20mA current loop — preferred for long cable runs because the current loop is immune to voltage-drop errors that affect 0-10V signals over distance.

How do the 8 selectable measuring ranges work?

An onboard jumper selects one of 8 measuring ranges, S0 through S7, each spanning a different temperature window. The factory default is S0 (-30 to 130°F), the widest range — useful when you don't yet know what range you need. Once you know your actual monitoring window, switching to a narrower range (e.g. S2 = 40-140°F for domestic hot water) gives you higher analog resolution because the same 0-10V or 4-20mA output span maps to a smaller temperature range. See the Selectable Measuring Ranges table on this page for all 8 options.

Does this need 24V power?

Yes. The 22MT-545 is an ACTIVE transmitter — it requires 24 VAC or 24 VDC power (21.6-26.4 VAC or 13.5-26.4 VDC). Power consumption is 0.8 VA AC / 0.4 W DC. This is the key difference from the passive 01-series equivalent: the 01-series sends raw resistance to the controller, while the 22-series outputs a scaled voltage or current after onboard signal conditioning. The advantage is compatibility with controllers that don't have Pt 1000 input curves; the cost is the need to provide 24V power to each sensor.

How do I install the probe across a coil face?

String the probe in a serpentine pattern across the duct cross-section, clipping it to the duct wall using the included A-22D-A08 brackets (6 supplied). Aim for roughly one foot of probe per square foot of duct cross-section, with the serpentine pattern covering the full face evenly. The transmitter housing mounts to the duct exterior using the included A-22D-A09 plate and routes into 1/2" NPT conduit via the included adapter.

How is this different from the passive 01MT?

The 01MT family is a passive resistance temperature sensor — it sends raw Pt 1000 (or NTC, Ni 1000) resistance to your controller, which must have a matching input curve. The 22MT family is an active 24V transmitter — it applies onboard signal conditioning and outputs a scaled 0-10V or 4-20mA signal. Choose passive when your BAS has Pt 1000/NTC inputs and you want fewer parts and no power supply concerns. Choose active (this product) when your BAS only accepts voltage/current analog inputs, when you need long cable runs (4-20mA versions are immune to voltage drop), or when you want the jumper-selectable range narrowing for higher resolution.

Does it work with my BAS?

Any BAS controller with a 4–20 mA analog input will read this transmitter directly. Set the controller input scale to match the selected measuring range (e.g., for S0 default, scale your input as -30°F = 0V/4mA, 130°F = 10V/20mA). No special curve or driver needed — it's a standard linear analog signal.