FMA902A-MA Hot Wire Air Velocity Transmitter w/Alarm Contact

Supported Applications

The Omega FMA900A Series is an industrial air velocity transmitter designed for measuring airflow in HVAC monitoring, exhaust and ventilation hoods, research and development laboratories, and manufacturing processes. The device utilizes a hot wire sensor design based on RTD elements to measure air velocity by detecting heat loss from the sensor as it cools in the moving medium.

Media compatibility is restricted to clean air or nitrogen only; use with other gases will produce measurement errors. Air carrying dust or oil can lead to coating of the sensor and inaccurate readings. The unit is not explosion-proof nor intrinsically safe, and must not be used for flammable or hazardous gases or in Hazardous areas.

Operating Conditions & Performance

The FMA900A Series operates within an ambient temperature range of 0 to 50°C (32 to 122°F) and a process temperature range of -40 to 93°C (-40 to 199°F). Accuracy is specified as 2% of FS or 15 FPM, whichever is larger. The response time for the sensor is 250 msec.

Measurement ranges are available from 0 to 200 FPM (0 to 1.02 m/sec) up to 0 to 10,000 FPM (0 to 50.8 m/sec). The manual also documents a range of 0 to 12,000 FPM (0 to 60.9 m/sec) for specific model configurations. As a bi-directional device, the transmitter provides identical readings whether airflow is in the forward or reverse direction and can be mounted vertically or horizontally without calibration shift.

Key Performance Specifications

• Accuracy: 2% of FS or 15 FPM, whichever larger
• Response Time: 250 msec
• Ambient Temperature: 0 to 50°C (32 to 122°F)
• Process Temperature: -40 to 93°C (-40 to 199°F)
• Power Supply: 15 to 24 Vdc @ 200 mA
• NIST Traceability: Optional up to 8,500 FPM (CAL-3-FLOW certificate available)

Configuration Options

The series offers configurable analog outputs and probe configurations tailored for specific installation needs. Output signals are selectable as either 0 to 5 Vdc or 4 to 20 mA, indicated by the suffixes "-V1" or "-MA" respectively in model numbers.

Probe Configurations

The sensor is housed in a stainless steel tube with inch marks for insertion depth reference. Three probe styles are available:

• Fixed Probe (Suffix A): Integrated unit where the transmitter and sensor are fixed together.
• Remote Probe (Suffix R): Features a 12" long remote probe with 15 feet of shielded cable, allowing separation between the sensing element and the electronics housing.
• Short Probe (Suffix S): A compact option featuring a 95 mm (3.75") short probe for applications requiring reduced insertion length.

Housing & Connections

The transmitter enclosure measures 89 H x 51 W x 32 mm D (3.5 x 2 x 1.25"). Electrical connections are made via a terminal block. The probe sheath is constructed of stainless steel with a diameter of 6 OD (¼" OD) and an insertion length of 305 mm (12") for standard probes.

Alarm Functionality

All models include one SPST relay contact closure for high alarm operation. The High Alarm Set Point is adjustable from 0 to 100% of the air flow range. Visual status indicators include a green power LED and a red LED for alarm indication.

Key Product Differences

Variants within the FMA900A Series are distinguished by measurement range, probe type (fixed vs. remote), output signal format, and physical length of the sensing element.

• Range Selection: Models correspond to specific velocity ranges: 200, 500, 1,000, 2,000, 5,000, or 10,000 FPM. The manual also lists a 12,000 FPM range for the FMA906 series.
• Output Suffixes: "-V1" denotes 0 to 5 Vdc output; "-MA" denotes 4 to 20 mA output. No additional cost is applied for selecting either output type.
• Probe Length Option: Adding the suffix "-S" configures the unit with a 95 mm (3.75") short probe instead of the standard length, at no additional cost.

Accessories available for this series include NIST traceable calibration certificates (CAL-3-FLOW), shielded cable spools (TX8-100), regulated power supplies (PSR-24S/PSR-24L), and compression fittings with PTFE ferrules (SSLK-14-14, T-FER-1/4).