ACI Humidity Sensor

ACI Humidity Sensors: Precision Measurement for Building Automation

ACI (Automation Components Inc.) has built a strong reputation as a leading manufacturer of relative humidity sensors engineered specifically for commercial HVAC and Building Automation System (BAS) applications. With operations based in Middleton, WI since 1991, ACI brings decades of focused expertise to one of the most critical measurements in any modern building: moisture control.

Why Humidity Measurement Matters in HVAC & BAS

Relative humidity directly impacts occupant comfort, indoor air quality, energy efficiency, and the longevity of mechanical systems. Too much moisture invites mold and structural damage; too little causes static discharge and respiratory discomfort. Reliable humidity sensors serve as the foundation for demand-controlled ventilation, dehumidification, and economizer strategies — making sensor accuracy a non-negotiable requirement for system designers and building engineers alike.

The A/RH Series: ACI's Core Humidity Sensor Lineup

ACI's A/RH Series Relative Humidity Transmitters utilize a capacitive humidity sensor element to deliver a proportional 4 to 20 mA, 0 to 5 volt DC, or 0 to 10 volt DC output. This flexible signal selection makes the line compatible with virtually any BAS controller on the market. The series spans three accuracy tiers — 1%, 2%, and 3% — so specifiers can balance precision requirements against budget constraints.

The A/RH2-R transmitter is engineered for precision in Building Automation Systems and demanding HVAC environments, utilizing a capacitive sensing element with a factory-fitted hydrophobic filter to ensure high-performance monitoring in spaces sensitive to dust, oils, and environmental chemicals. Its ±2% RH accuracy at 77°F (25°C) from 10% to 95% makes it a standard for humidity control in pharmaceutical facilities, hospitals, and clean rooms.

Mounting Configurations for Every Application

The A/RH3 Series relative humidity transmitters are specifically designed for use in HVAC/BAS applications and are available for room, duct, outside air, and stainless steel wall plate applications. Outside air models step up the durability ante: outside air configurations feature a weatherproof Euro-style enclosure with a gasketed cover and conformally coated circuit boards for added moisture and chemical resistance.

• Room Sensors — Low-profile enclosures with four-way ventilation to minimize self-heating and deliver accurate ambient readings in offices, labs, and clean rooms.
• Duct Sensors — Specifically designed to monitor and control humidity in air ducts, available in standard plastic Euro-style and ruggedized NEMA 4X enclosures.
• Outside Air Sensors — Built to withstand harsh environmental exposure, with conformally coated PCBs and weatherproof housings.
• Combo RH + Temperature Sensors — ACI humidity sensors can be paired with temperature sensor(s) to reduce installation costs, combining two critical measurements into a single device.

Key Features That Set ACI Apart

ACI humidity sensors are durable, accurate, reliable, and backed by a five-year warranty on the entire device. They can be field calibrated to reduce operating costs. On-board DIP switches allow the user to select the desired output signal, and single-point field calibration can be performed by using the increment and decrement calibration DIP switches to adjust the curve in ±0.5% increments with each toggle.

Each A/RH3 Series humidity transmitter is calibrated using a NIST Traceable Temperature/Humidity Chamber, with three- and five-point NIST calibration certificates available as an option. For applications requiring documented traceability — such as pharmaceutical manufacturing or laboratory environments — this level of quality assurance is essential.

ACI is committed to American manufacturing: they engineer, design, and manufacture products in one of their four facilities in Middleton, WI. That domestic production chain supports consistent quality control and reliable lead times for contractors and systems integrators working on tight project schedules.