Testo 605i Thermohygrometer

The Testo 605i is a thermohygrometer in the Testo Smart Probes family. It measures relative humidity and air temperature in ducts, at registers and grilles, and in rooms, and dew point and wet bulb are calculated from those two readings. The probe has no display of its own and sends readings over Bluetooth to measureQuick or the testo Smart App. On the current second-generation probe the sensor shaft folds to 90° to reach into a grille, and Testo rates the Bluetooth range at up to 350 ft.

Humidity and Temperature Measurement

A capacitive humidity sensor reads 0 to 100% RH at 0.1% RH resolution. Testo rates it at ±2.0% RH from 35 to 65% RH, ±3.0% RH from 10 to 35% and from 65 to 90% RH, and ±5.0% RH below 10% or above 90% RH, all at 77 °F (25 °C). An NTC sensor reads air temperature from -4 to 140 °F (-20 to 60 °C) at ±0.9 °F (±0.5 °C) above 32 °F and ±1.4 °F (±0.8 °C) below it. The 2.9 in. shaft is 0.5 in. in diameter, sized for in-duct readings through a test port.

measureQuick Wireless Integration

The 605i connects to measureQuick over Bluetooth alongside the other Testo Smart Probes on the job. Testo pairs two 605i probes for heating and cooling capacity work, one in the return and one in the supply, and in measureQuick that pair supplies the dry bulb and humidity on both sides of the coil for the temperature split and psychrometric calculations. Readings go into the test record with no hand transcription, recorded with the airflow, static pressure, and refrigerant readings from the same test.

Build and Field Readiness

The 605i measures 8.6 x 1.2 x 1.0 in. and runs about 150 hours on three AAA batteries. It operates from -4 to 122 °F (-20 to 50 °C), ships with batteries and a calibration certificate, and carries a 2-year Testo warranty.