HD5XMSTH Schneider Duct Probe Humidity Temperature Transmitter Economy Grade 4-20mA 10k Thermistor

The HD5XMSTH is a duct-mounted temperature and humidity transmitter designed for HVAC applications. This economy grade device is ideal for volume applications where large air handling units require air condition monitoring without the expense of instrument grade sensors.

It measures both relative humidity and temperature using a single probe inserted into the duct, requiring only one penetration and one cable for both readings. The humidity element features a thin film capacitive type that remains stable over time and recovers effectively from saturation events. Temperature measurement is provided by a 10kΩ type 3 thermistor, compatible with Schneider controllers as standard. The humidity channel delivers a current output that universal inputs can accept directly without signal conditioning.

Proper sensor positioning is critical for accurate measurements. In humidification or cooling coil applications, the choice between upstream and downstream measurement significantly impacts reading interpretation:

• Upstream measurement indicates load conditions
• Downstream measurement shows results
• Using incorrect positioning can create conflicting control loops

Stratification is another important consideration. Probes placed in short ducts immediately after coils or fans may encounter unrepresentative air mixtures. The practical solution is to position measurements in straight sections with adequate distance from disturbances.

This transmitter is primarily used in air handling units where supply and return humidity measurements control humidification, dehumidification, and coil capacity:

• Return air measurement: Establishes plant load conditions
• Mixed air measurement: Sets economiser thresholds
• Cleanrooms and laboratories: Supports room condition monitoring
• Hospitals: Operating theatre and isolation plant humidity control
• Swimming pools and leisure centres: Condensation control and building protection
• Commercial offices: Drives economiser and ventilation strategies based on conditions rather than fixed schedules