Testo 6721 Dew Point Switch

0555 6721


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  • Detects moisture in compressed air systems
  • Measurement range -30 to 30°C (-22 to 86°F)
  • Optional alarm box available
  • Easy configuration with P2A software
  • Uses proven Testo humidity sensor
  • Mini DIN interface

The Testo 6721 dew point switch measures the temperature pressure dew point (tpd) coming from refrigeration dryers or downstream in pneumatic machines and processes from -30 to 30°C (-22 to 86°F) up to 300 psi (20 bar). Moisture in compressed air lines can lead to expensive damage: icing, corrosion, water hammer, sticky and clogged materials. The Testo 6721 dew point switch can save time, money and system downtime by monitoring moisture and avoiding damage.

The Testo 6721 dew point switch uses Testo's proven RH sensor design for accurate temperature pressure dew point measurements. It's easily installed in dryer and compressed air lines via its 1/2" NPT threaded fitting.

The Testo 6721 dew point switch can be configured using the optional Testo P2A software via USB cable and the data port on the 6721 switch. The software can easily program, adjust and review the 6721 operating history while connected to a laptop or PC. The user can even save a "master" program file that provides easy "copy and paste" program replication for OEM requirements. An optional alarm box (0554 6722) provides visual confirmation of both pre and alarm conditions.

Testo 6721 Dew Point Switch Specifications

Feature Testo 6721
Measuring range -30 to 30°C (-22 to 86°F)
Accuracy ±4 K (-30 to -20°C)(-22 to -4°F)
±3 K (-20 to -10°C)(-4 to 14°F)
±2 K (-10 to 0°C)(14 to 32°F)
±1 K (>0°C)(>32°F)
Sensor Testo humidity sensor (with special trace humidity adjustment) and NTC temperature sensor
Process pressure Max. 20 bar (abs)(290 psi)
Process temperature 0 to 50°C (32 to 122°F)
Outputs 2x switches potential-free max. 30 V/0.5 A
Interface Mini-DIN interface (serial) for parameterization / adjustment / analysis via P2A software
Voltage supply 20 to 30 VAC/VDC

Power Supplies

Testo Power Supply
Wall-mountable 110-240 VAC box power supply
Testo DIN Rail Power Supply
DIN rail mountable 90-240 VAC power supply


Testo P2A Software Package
Parameterizing, adjusting and analyzing software with USB cable and adaptor


Please consider these optional accessories.

Testo Measurement Chamber
Measuring Chamber for Testo Dew Point Transmitters
Testo Cooling Coil
Cooling coil for Measuring Chamber
Testo RH Calibration Set
Perform quick checks or full calibrations for humidity probes