The ACI Platinum Outside Air Series is a single-point weatherproof outdoor RTD sensor for building management systems and PLCs that accept a platinum resistance input. The element is double encapsulated in thermally conductive epoxy and terminates in etched Teflon lead wires color coded by sensor type. The three-wire configuration adds a third lead that compensates for external lead-wire resistance, and ACI recommends 18 AWG field wiring on platinum RTD runs to keep that resistance low.
Specifications sourced from the ACI Platinum RTD Outside Air Data Sheet and ACI Outdoor Series Installation & Operation Instructions (Version 5.0). Verified against ACI source documentation on 26 August 2026.
Best For
- Outside Air Temperature Sensing
- Cold Storage Facilities
- High Dew Point / Condensing Environments
Key Features
Double-Encapsulated Element
One sensing point built with ACI's double encapsulation process and thermally conductive epoxy, which ACI specifies to eliminate the effects of moisture on the sensor.
Bell Box Enclosure
Aluminum, rated NEMA 3R, with an enclosure operating range of -40 to 121 C (-40 to 250 F).
Color-Coded Teflon Leads
Two 14 in (35.6 cm) 22 AWG etched Teflon leads in Brown/Brown identify the curve at the panel and resist outdoor exposure.
Shaded-Mount Design
Intended for eave or north-wall mounting with the sensing tube pointed downward so water and ice cannot settle inside the tube.
Direct Controller Connection
Passive element wires straight into an analog input with no transmitter or power supply. The controller input must be set to the matching sensor curve.
Five-Year Coverage
Backed by the ACI Five (5) Year Limited Warranty. A NIST Certificate (3 points) is available on the same part number by adding the -NIST suffix.
Technical Specifications
| Sensor Type | Sensor Curve | Platinum RTD | PTC (Positive Temperature Coefficient) |
|---|---|
| Number of Sensing Points | One |
| Number of Wires | Two (non-polarity sensitive) |
| Sensor Output | Lead Wire Colors | 100 Ohms nominal at 0 C (32 F) | Brown/Brown |
| Sensor Accuracy | +/-0.06% Class A. Tolerance formula: +/- C = 0.15 C + (0.002 x |t|), where |t| is the absolute temperature above or below 0 C in C |
| Accuracy at Reference Points | -40 C (-40 F): +/-0.23 C (+/-0.414 F) | 0 C (32 F): +/-0.15 C (+/-0.27 F) | 70 C (158 F): +/-0.29 C (+/-0.53 F) |
| DIN Standard | Temperature Coefficient | DIN EN 60751 (IEC 751) | 3850 ppm/C |
| Sensor Stability | +/-0.03% after 1000 hours at 300 C (572 F) |
| Self-Heating | Maximum Operating Current | 7 mW/C in still air | 5 mA maximum operating current |
| Response Time (63% Step Change) | 25 seconds nominal (63% step change) |
| Operating Temperature Range | -40 to 70 C (-40 to 158 F) |
| Storage Temperature Range | -40 to 70 C (-40 to 158 F) |
| Operating Humidity Range | 0 to 100% RH, condensing |
| Lead Length | Conductor Size | 14 in (35.6 cm) | 22 AWG (0.65 mm) |
| Lead Wire Insulation | Wire Rating | Etched Teflon (PTFE) colored leads | MIL-W-16878/4 (Type E) |
| Conductor Material | Silver plated copper |
| Enclosure Material | Aluminum |
| Enclosure Operating Temperature Range | -40 to 121 C (-40 to 250 F) |
| Enclosure Flammability Rating | Not published (metal enclosure) |
| Enclosure NEMA / IP Rating | NEMA 3R |
| Product Dimensions | See dimensional drawing on the back page of the data sheet |
| Product Weight | 0.76 lbs (0.35 kg) |
| Agency Approvals | CE, RoHS2, WEEE |
Documentation
ACI Platinum RTD Outside Air Data Sheet- ACI Outdoor Series Installation & Operation Instructions (Version 5.0)
Related Products
- ACI A/100-2W-O-EH : Weatherproof Outside Air Temperature Sensor, 100 Ohm Platinum RTD, 2-Wire, Plastic Euro Enclosure
- ACI A/100-2W-O-4X : Weatherproof Outside Air Temperature Sensor, 100 Ohm Platinum RTD, 2-Wire, Plastic NEMA 4X Enclosure
Frequently Asked Questions
What is the sensor output of the A/100-2W-O-BB?
This unit reads 100 Ohms nominal at 0 C (32 F) with Brown/Brown lead wires. It is a passive element, so the controller supplies the excitation and resolves the temperature from the resistance curve.
Does the A/100-2W-O-BB need a transmitter?
No, provided the controller input is configured for the matching curve. If the run is long, the input is current-only, or the reading must be scaled at the sensor, use the ACI TT or TTM Outside Air transmitter series instead.
Where should the A/100-2W-O-BB be mounted?
Mount it in shade on the north side of the structure (south side in the southern hemisphere), 1 to 2 ft (0.3 to 0.6 m) below the eave and at least 4 ft (1.22 m) above grade. The sensing tube must point downward so water, ice and debris cannot settle inside it. Avoid chimney walls, vents, doors, dampers and locations above windows.
What is the Bell Box enclosure rated for?
The Aluminum NEMA 3R Enclosure is Aluminum, rated NEMA 3R, with an enclosure operating range of -40 to 121 C (-40 to 250 F).
What is the warranty on the A/100-2W-O-BB?
ACI covers this series under its Five (5) Year Limited Warranty. The full text is published in the front of the ACI Sensors and Transmitters catalog and on workaci.com.
ACI Five (5) Year Limited Warranty. This series is covered by ACI's Five (5) Year Limited Warranty. ACI publishes the full warranty terms in the front of the ACI Sensors & Transmitters catalog and on workaci.com; refer to that document for the scope of coverage.
- Sensor Type:
- Outside Air
- Output Signal:
- Temperature Only
- CO2 Element:
- None
- Humidity Element:
- None
- VOC Element:
- None
- Temperature Element:
- 100 Ohm Platinum RTD
- Display:
- None
- Supported Protocols:
- None
- Enclosure:
- Aluminum NEMA 3R
- NIST Certificate:
- No
