The ACI Transmitter Outside Air Series pairs a Class A platinum RTD with an onboard temperature transmitter so the outdoor reading arrives at the controller as a scaled analog signal instead of a raw resistance. The 4-20 mA version is two-wire loop powered; the 1-5 VDC and 2-10 VDC versions are three-wire. Zero and span potentiometers allow field recalibration against NIST-certified reference equipment, and every unit ships in a weatherproof enclosure with 1/2 in knockouts or 1/2 in NPT threaded hubs for installation.
Specifications sourced from the ACI Transmitter Outside Air Data Sheet and ACI Outside Air Series Temperature Transmitter Installation & Operation Instructions (Version 2.0). Verified against ACI source documentation on 26 August 2026.
Best For
- Outside Air Temperature Sensing
- Economizer Control
- Cold Storage Facilities and Warehouses
- High Moisture Environments
Calibrated span is built to order. Specify the low and high temperature span in F or C on your purchase order. Minimum span 50 F (28 C), maximum span 300 F (148 C); ACI notes best accuracy in 100 F increments.
Key Features
Single-Point Outdoor Assembly
One platinum RTD sensing point paired with the transmitter board, supplied in a weatherproof enclosure with 1/2 in knockouts or 1/2 in NPT threaded hubs.
NEMA 4X Enclosure
Polystyrene Plastic, rated NEMA 4X (IP66), with an enclosure operating range of -40 to 70 C (-40 to 158 F).
Scaled Analog Output
2-10 VDC Output, three-wire, so the controller sees a linear signal rather than a raw resistance curve.
Field Recalibration
Onboard zero and span potentiometers allow adjustment against NIST-certified reference equipment. ACI also offers factory recalibration on returned transmitters.
Class A Platinum Element
+/-0.06% Class A RTD to DIN EN 60751 (IEC 751), 3850 ppm/C, for repeatable outdoor measurement across the calibrated span.
Loop-Friendly Power
Accepts +8.5 to 32 VDC, reverse polarity protected, 25 mA per transmitter, so multiple units can share one supply.
Technical Specifications
| Output Signal | Wiring | 2-10 VDC Output | Three-wire |
|---|---|
| Transmitter Supply Voltage | Supply Current | +8.5 to 32 VDC (reverse polarity protected) | 25 mA minimum |
| Minimum Supply Voltage for This Output | +18.5 to 32 VDC (500 Ohm load) |
| Maximum Load Resistance | (Terminal Voltage - 8.5 V) / 0.020 A |
| Calibrated Accuracy | Linearity | Temperature spans below 500 F (260 C): +/-0.2%. Calibrated at 71 F (22 C) nominal |
| Thermal Drift | Spans below 100 F (38 C): +/-0.04%/F | Spans above 100 F (38 C): +/-0.02%/F |
| Minimum | Maximum Calibrated Temperature Span | 50 F (28 C) | 300 F (148 C) |
| Warm Up Time | Warm Up Drift | 10 minutes | +/-0.1% |
| Transmitter Operating Temperature Range | -40 to 185 F (-40 to 85 C) |
| Zero and Span Adjustment | Onboard potentiometers for field recalibration |
| Connections | Wire Size | Screw terminal blocks (polarity sensitive) | 16 AWG (1.31 mm2) to 26 AWG (0.129 mm2) |
| Terminal Block Torque Rating | 0.37 ft-lb (0.5 Nm) nominal |
| Sensor Type | Sensor Curve | Sensing Points | Platinum RTD | PTC (Positive Temperature Coefficient) | One |
| Sensor Resistance | Lead Wire Colors | 1000 Ohms nominal at 0 C (32 F) | Black/Black |
| RTD Tolerance Class | 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 |
| Sensor DIN Standard | Temperature Coefficient | DIN EN 60751 (IEC 751) | 3850 ppm/C |
| Sensor Response Time (63% Step Change) | 8 seconds nominal (I0000857 v2.0 installation instructions; not stated in the data sheet) |
| Operating | Storage Temperature Range | -40 to 71 C (-40 to 160 F) |
| Sensor Operating Humidity Range | 0 to 100% RH (data sheet) |
| Transmitter Operating Humidity Range | 0 to 90% RH, non-condensing (I0000857 v2.0 installation instructions) |
| 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 |
| Cord Grip Fitting Material | Flammability | Polyamide 6.6 | UL94-V2 (included with the -4X enclosure option only) |
| Cord Grip Seal Material | NEMA / IP Rating | Neoprene | IP68 (NEMA 4X) |
| Cord Grip Torque Recommendation | 1.83 ft-lbs (2.50 Nm) |
| Enclosure Material | Polystyrene Plastic |
| Enclosure Operating Temperature Range | -40 to 70 C (-40 to 158 F) |
| Enclosure Flammability Rating | UL94-V2 |
| Enclosure NEMA / IP Rating | NEMA 4X (IP66) |
| Product Dimensions | See dimensional drawing on the back page of the data sheet |
| Product Weight | 0.41 lbs (0.180 kg) |
| Agency Approvals | RoHS2, WEEE |
Documentation
ACI Transmitter Outside Air Data Sheet- ACI Outside Air Series Temperature Transmitter Installation & Operation Instructions (Version 2.0)
Related Products
- ACI A/TT1K-O-2-EH : Outside Air Temperature Transmitter, 1K Ohm Platinum RTD, 2-10 VDC Output, Plastic Euro Enclosure
- ACI A/TT1K-O-2-BB : Outside Air Temperature Transmitter, 1K Ohm Platinum RTD, 2-10 VDC Output, Aluminum NEMA 3R Enclosure
Frequently Asked Questions
What temperature span does the A/TT1K-O-2-4X ship with?
The calibrated span is specified at the time of order and is not a stock attribute. The minimum span is 50 F (28 C) and the maximum span is 300 F (148 C); ACI notes best accuracy is achieved in 100 F increments. Provide the required low and high span values with your purchase order.
What supply voltage does the A/TT1K-O-2-4X need?
The transmitter accepts +8.5 to 32 VDC and is reverse polarity protected, drawing 25 mA minimum. For this 2-10 VDC Output version the practical minimum is +18.5 to 32 VDC (500 Ohm load). ACI transmitters do not accept an AC input.
Should I order the TT or the TTM version?
TT part numbers supply the Class A RTD and transmitter as standard components. TTM part numbers are ACI's matched configuration and include a 3-point NIST Certificate by default. Choose TTM when ACI's matched configuration and the included 3-point NIST Certificate are required for the application.
Where should the A/TT1K-O-2-4X 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 NEMA 4X enclosure rated for?
The Plastic NEMA 4X Enclosure is Polystyrene Plastic, rated NEMA 4X (IP66), with an enclosure operating range of -40 to 70 C (-40 to 158 F).
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.
ACI offers recalibration service for transmitters returned to the factory, for a nominal fee.
- Sensor Type:
- Outside Air
- Output Signal:
- 2-10 VDC
- CO2 Element:
- None
- Humidity Element:
- None
- VOC Element:
- None
- Temperature Element:
- 1K Ohm Platinum RTD
- Display:
- None
- Supported Protocols:
- None
- Enclosure:
- NEMA 4X
- NIST Certificate:
- No
