Starting at $666.00 Starting at $599.40
  • Usually ships in 3-4 weeks



  • Range: 0 to 100%RH (6681 model only).
  • Accuracy: up to ±1%RH
  • Plastic housing (model 6651)
  • Metal housing (model 6681)
  • 2-line LCD
  • Resolution: 0.1%RH
  • Operating Temperature: -40 to 70°C (-40 to 158°F)
  • Digital plug-in probe connection
  • Model 6651
    • Measurement Range (probe dependent): -20 to 120°C (-4 to 248°F)
    • Measurement Parameters: °C/°F, %rF/%RH, °Ctd / °Ftd
  • Model 6681
    • Measurement Range (probe dependent): -20 to 180°C (-4 to 356°F)
    • Measurement Parameters: °C/°F, %rF/%RH, °Ctd / °Ftd, °Ctpd / °Ftpd, more


The Testo 6651 and 6681 humidity transmitters are designed for demanding, critical climate and drying process applications. The optional display has an easy-to-use operating menu allowing for most adjustments to be performed on-site without the use of a PC. Password protection prevents access by unauthorized users.

Like all Testo transmitters, the Testo 6651 and 6681 feature the P2A software. The analysis tools incorporated in the software test analog and relay signals and display min/max values. The transmitter software also includes an operational hour counter which means reports are stored with a time/date stamp to provide a history of error events.

The functionality of the Testo 6651 and 6681 transmitters is largely dependent on the digital probe chosen for the application. The probes come adjusted and calibrated, ready for use. The digital interface to the transmitter allows the probes to be exchanged by hand, limiting transmitter down-time. Each probe has its own serial number and memory which stores adjustment history and an operational hour counter.

The Testo 6651 adjustment buttons, test points and interfaces are located on the front of the transmitter for easy access. The wiring is contained separately, in its own spacious wiring compartment. The Testo 6651 is available in a duct mount version where the transmitter is not mounted separately, but simply pushed over the end of the probe and held in place.

The Testo 6681 humidity transmitter is the ideal choice for demanding, humidity measurement applications beyond the capabilities of the Testo 6651. Testo 6681 feature accuracy up to ±1%RH, metal housing, field bus connection via Profibus-DP and humidity parameters such as absolute humidity and enthalpy.

Several different probes are available for use with the Testo 6681. The Testo 6617 probe is considered the "early warning humidity probe". Ideal for preventative maintenance, this probe continuously monitors the Testo humidity sensor for any symptoms of beginning corrosion, avoiding costly measurement errors and system downtime. The Testo 6614 digital probe is a high humidity probe, stable enough for continuous high humidity processes. The Testo 6615 probe measures trace humidity and features an auto-adjustment and high accuracy.

Applications for the Testo 6651/6681

  • Critical climate
  • Cleanrooms
  • Drying processes (6681)
  • High humidity (6681)
  • Trace humidity (6681)
  • Humidity in H2O2

***Probes are not included with the Testo 6651/6681 Humidity Transmitter and must be purchased as accessories.***