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  • Measuring range: -90 to 30°Ctd (-130 to 86°Ftd)
  • Condensation-proof sensor with sol-gel technology guarantees fast response
  • Multi-language display and user-menu
  • Automatic self-adjustment ensures high accuracy and long reliability
  • P2A software available for setting/adjusting parameters and data analysis


The Testo 6781 trace humidity/dew point transmitter is used to monitor trace humidity in air, compressed air and gases. Used in all areas of industry, humidity in compressed air and gases is normally undesirable because it can cause damage to machinery or impair the quality of the end product.

The Testo 6781 humidity/dew point transmitter is an excellent option for applications that need humidity monitoring/control to meet standard ISO 8573 Class 1 and Class 2 compliance. The Testo 6781 has a measuring range from -90 to 30°C (-130 to 86°F). It features a condensation-proof sensor with sol-gel technology to guarantee the fastest response time. The automatic self-adjustment reduces operating costs and ensures high accuracy and reliability.

The Testo 6781 is compatible with Testo P2A software which allows for parameterization of unit and scale, sensor adjustment, analog output adjustment and access to adjustment history which can all be transferred to a PC for data storage and analysis. The self-monitoring transmitters guarantee high system availability.

Applications for the Testo 6781 Humidity Transmitter

  • Compressed air systems: dryer monitoring to avoid damage caused by humidity
  • Medical compressed air: minimum humidity as a hygiene requirement
  • Granulate drying: dry air is a requirement for product quality
  • Gas engineering: humidity causes damage and reduces the value os the gas in the system

Testo 6781 Humidity Transmitter Specifications

Humidity Parameters
Units °Ctd, °Ftd, %rF, % RH
Calculated variables °CtdA, °FtdA(normed atmosph.dew point), ppmV, g/m3, g/ft3, g/kg, g/lb
Measuring range -90 to 30°Ctd / -130 to 86°Ftd
Measurement uncertainty -20°Ctd to -40°Ctd: ±1.5K
-40°Ctd to -60°Ctd: ±2K
-60°Ctd to -75°Ctd: ±2.5K
Automatic self-adjustment Cycle adjustable: 1h/6h/12h/24h
Analog outputs
Current/accuracy 0 to 20 mA ±0.03 mA (4-wire)
4 to 20 mA ±0.03 mA (4-wire)
Output type 0 to 1 V ±1.5 mV (4-wire)
0 to 5 V ±7.5 mV (4-wire)
0 to 10 V ±15 mV (4-wire)
Measuring cycle 1/sec
Resolution 12 bit
Load max. 500 Ω
Other outputs
Digital Mini-DIN for P2A software
voltage supply 20 to 30 VAC/DC, 300 mA current consumption, galvanically separate signal and supply line