Therm-Duct

Supported Applications

The ACI Thermistor Duct Series consists of single-point temperature sensors designed for use with electronic controllers in commercial heating and cooling building management systems. These sensors are intended specifically for duct applications to monitor air temperatures.

To ensure accurate readings, the product overview specifies that the sensor should be mounted on the top or sides of duct work where air circulation is well mixed (no stratification) and not blocked by obstructions. The probe placement recommendation is 3 to 4 duct segments down from any bend or obstruction and away from 90° bends.

Operating Conditions & Performance

The series utilizes a Non-Linear, NTC (Negative Temperature Coefficient) thermistor sensor with a measurement range of -40°C (-40°F) to 150°C (302°F). The probe features a 0.250" (6.35 mm) diameter constructed from 304 Stainless Steel.

Accuracy Specifications

Sensor accuracy varies by series and temperature point:

• A/1.8K Series: +/- 0.5°C @ 25°C (77°F) and (+/-1.0°C) (+/-1.8°F)
• A/10K-E1 Series: +/- 0.3°C (+/- 0.54°F)
• All other thermistors: +/- 0.2°C (+/- 0.36°F) from 0-70°C (32 - 158°F)

The nominal response time is listed as 10 seconds for a 63% step change.

Environmental Limits by Enclosure

Operating temperature limits depend on the selected enclosure:

• -GD (Galvanized Steel): -40 to 115°C (-40 to 239°F), NEMA 1 (IP10)
• -PB (ABS Plastic): -30 to 90°C (-22 to 194°F), Plenum Rated, UL94-HB
• -BB (Aluminum): -40 to 121°C (-40 to 250°F), NEMA 3R, Plenum Rated
• -4X (Polystyrene Plastic): -40 to 70°C (-40 to 158°F), NEMA 4X (IP 66)

The series operates in humidity ranges of 10 to 95% RH, non-condensing. Storage temperature is rated from -40 to 85°C (-40 to 185°F).

Configuration Options

The ACI Thermistor Duct Series offers extensive configuration options for sensor curves, probe lengths, and enclosure types.

Sensor Elements & Output Signals

Multiple thermistor series are available with specific nominal resistances at 25°C (77°F) and distinct lead wire color codes:

• A/1.8K: 1.8 KΩ nominal (Red/Yellow)
• A/3K: 3 KΩ nominal (White/Brown)
• A/AN (Type III): 10 KΩ nominal (White/White)
• A/AN-BC: 5.238 KΩ nominal (White/Yellow)
• A/CP (Type II): 10 KΩ nominal (White/Green)
• A/CSI: 10 KΩ nominal (Green/Yellow)
• A/10KS: 10 KΩ nominal (White/Blue)
• A/10K-E1: 10 KΩ nominal (Gray/Orange)
• A/20K: 20 KΩ nominal (Brown/Blue)
• A/50K: 50 KΩ nominal (Brown/Yellow)
• A/100KS: 100 KΩ nominal (Black/Yellow)

Probe Lengths & Mounting

Sensors are available with probe lengths of 4", 6", 8", 12", and 18". The series includes an insulation pad for sealing the duct and dampening vibration; all enclosures have a foam pad attached, while the "DO" (no enclosure) option includes but does not pre-install the pad.

Enclosure Options

The following housing configurations are offered:

• -GD: Galvanized Enclosure
• -PB: Plastic Box with hinged cover
• -BB: Bell Box (Aluminum)
• -4X: NEMA 4X Weatherproof Enclosure
• -DO: Without Box (Polyamide 66 High Performance Nylon fitting, UL94-HB)

Electrical & Certification Options

Sensors feature two non-polarity sensitive wires with 22 AWG Etched Teflon colored leads. Optional NIST certificates are available for specific configurations.

Key Product Differences

The series distinguishes between standard thermistor sensors and the A/10K-E1 Series, which carries a different accuracy specification (+/- 0.3°C). The A/1.8K Series also differs in power dissipation constant (1 mW/°C) compared to other models.

Enclosure variations define the environmental protection level and operating temperature range: the -PB enclosure is Plenum Rated with a lower maximum operating temperature (-30 to 90°C), while the -4X enclosure provides NEMA 4X (IP 66) rating but operates only up to 70°C. The -BB Aluminum Bell Box supports temperatures up to 121°C and carries both Plenum Rated and NEMA 3R designations.

Lead wire lengths vary by probe size: 4", 6", and 8" probes include 14" (35.6 cm) leads, while 12" and 18" probes include 24" (61 cm) leads.