Belimo 01MT-5L8 Passive Averaging Duct Temperature Sensor NTC10k 50 ft Probe

The Belimo 01MT-5L8 is a passive flexible cable averaging temperature sensor designed for accurate air temperature measurement across large duct cross-sections, coil faces, and mixing plenums in commercial and industrial HVAC systems. Featuring a 50 ft (15 m) flexible probe with an NTC 10K Type II (10k2) multi-point sensing element, this sensor delivers a single true averaged temperature reading rather than a potentially biased single-point measurement.

The probe is strung serpentine across the face of a coil, mixing box, or large duct to capture temperature variations across the entire cross-section. This averaging method eliminates errors caused by air stratification, making it ideal for applications where temperature uniformity cannot be assumed. Because it is a passive resistive device, no 24V power supply is required — it connects directly to a controller input.

Key Features:

• Sensing Element: NTC 10K Type II (10k2) — industry-standard multi-point thermistor
• Probe Length: 50 ft (15 m) flexible cable
• Measuring Range: -30 to 120°F (-35 to 50°C)
• Accuracy: ±0.35°F at 77°F (±0.2°C at 25°C)
• Measuring Current: <2 mA @ 77°F (25°C)
• Time Constant (τ 63%): Typical 100 seconds at 0 m/s air velocity
• Enclosure Rating: NEMA 4X / IP65 UV-resistant polycarbonate housing
• Electrical Connection: Pluggable spring-loaded terminal block
• Power Required: None — passive resistance element (no 24V supply needed)
• Pollution Degree: 3
• Ambient Humidity: Max 95% RH, non-condensing
• Warranty: 5-year factory warranty

Included in the Box:

• Mounting plate
• 2x mounting kit with 6 mounting brackets
• 1/2" NPT conduit adapter

The 01MT-5L8 is well-suited for defeating air stratification on cooling and heating coil discharge, mixed-air plenums, large supply and return ducts, and AHU plenums where outdoor and return air have not yet fully mixed. It is particularly effective in freeze protection and economizer changeover applications where cold spots near coil edges must not be missed.