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Wirelessly Monitoring Air Duct Temperature

Wireless Measuring temperature inside an air duct is a common facilities maintenance task for energy conservation, particularly when office area temperatures are far from defined set-points. Historically, maintenance staff have stood on a ladder holding an RTD probe inside an air duct with one hand, the connector on the probe plugged into a handheld thermometer held with the other hand. The maintenance tech will then read the duct temperature off an LCD display. A wall-mount data logger cannot be used to record data over long periods of time, as it cannot fit inside the duct. The handheld thermometer cannot be used for logging data because it cannot be attached to the duct. Hence, the maintenance person will be standing on the ladder for a long and uncomfortable time while he tries to obtain data. With a UWBT temperature transmitter fitted with an M12 probe connector, the maintenance technician has a much less cumbersome way of gathering data.

In this application a PR-25AP air temperature RTD probe is screwed in via its M12 connector to a UWBT-RTD transmitter. The technician first pairs the transmitter to a smart device, attached to his person or conveniently located on a nearby bench. He then sets sensor settings, begins the data logging process, climbs on a ladder, and inserts to probe tip into the air duct. The app displays 28.0°C (82.4°F), a very warm temperature for an office environment, indicating that something is wrong with the building temperature control system. When the technician clicks the light green colored icon for “Start Logging”, the app screen changes. The red icon showing “Rec” indicates that data logging is in process.

The PR-25AP air temperature RTD probe is well designed for this application. It combines the high accuracy RTD sensor found in the OMEGA® Ultra-Precise RTD probes with the convenience and reliability of an M12 connection. The PR-25AP comes standard with a Pt100 Wire Wound RTD calibrated to Class A Accuracy Standard of IEC 60751. The probe tip is designed to provide a barrier to airflow between the air stream and the ambient conditions. It has been tested to 400 psi with no leakage. The probe is constructed with a 316L stainless steel housing and sheath for strength and corrosion resistance.

In certain situations, the technician may want to leave an RTD probe inserted into the duct for an extended time, walk away to accomplish another task, and log temperature data internally. The RTD-805 air temperature RTD sensor is well suited for this situation. The technician would use transmitter model UWBT-RTD-TB with this sensor, as this model comes standard with a 3 position terminal block for connecting the loose wires of the sensor.

The RTD-805 sensor is available with either a stainless steel or plastic housing. Similar to the PR-25AP probe, it comes standard with a 3-wire Pt100 Wire Wound RTD calibrated to Class A Accuracy Standard of IEC 60751. The technician would connect the three wires of the sensor to the terminal block located on the front face of the transmitter. The tip of the sensor would be inserted into the air duct. The technician can loosely place the transmitter inside a ceiling tile, as it weighs only 0.38 lb (0.13 kg). The technician would pair with the transmitter and start the internal data logging process. He could record log duct temperature data at 1 sample/minute for up to 150 hours of battery life, and come back at a later time to download the data to his smart phone. The data could be conveniently emailed to other maintenance staff, with subsequent analysis made of the air temperature control system in the building.

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