testo 645 - Humidity/temperature measuring instrument

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High-precision humidity measurement up to ± 1% RH
Internal reading memory (3,000 readings)
High-precision humidity measurement up to ± 1% RH
Possibility of attaching a really wide range of optional probes thanks to a large accessory portfolio


Product Description

The testo 645 high-precision humidity and temperature measuring instrument offers two probe inputs for attaching a comprehensive range of probes:     

Channel 1: temperature probe, type K/J/S, NTC     

Channel 2: humidity/temperature probe or Pt 100 temperature probe  

At the touch of a button, the thermohygrometer automatically indicates the measurement parameters of temperature, relative humidity, dew point, pressure dew point, absolute humidity, degree of humidity and enthalpy, along with min., max. and mean values, as well as the last measured value. Convenient evaluation of the measurement data is possible using the optional PC software. Measurement data can also be printed out directly at the measuring location via the optional testo fast printer.

Areas of application of the testo 645 humidity/temperature measuring instrument 

Monitoring of temperature and humidity values in production, storage and server rooms, museums, archives, cold stores, containers and display cases     

Location of mould formation in residential or other buildings  

Delivery Scope

testo 645 humidity/temperature measuring instrument, including battery.

Temperature - Pt100

Measuring range
 -200 to +800 °C
Accuracy ±0.1 % of mv (200.1 to 800 °C)
±0.2 °C (-200 to 200 °C)
Resolution 0.1 °C


Temperature - NTC

Measuring range
 -50 to +150 °C
Resolution 0.1 °C


Temperature - TC Type K (NiCr-Ni)

Measuring range
 -200 to +1370 °C
Resolution 0.1 °C
Accuracy ±0.5 % of mv (-200 to -60.1 °C)
±0.5 % of mv (+60.1 to +1370 °C)
±0.3 °C (-60 to +60 °C)


Temperature - TC Type J (Fe-CuNi)

Measuring range
 -40 to +750 °C
Resolution 0.1 °C
Accuracy ±0.5 % of mv (-200 to -60.1 °C)
±0.5 % of mv (+60.1 to +750 °C)
±0.3 °C (-60 to +60 °C)


Temperature - TC Type S (Pt10Rh-Pt)

Measuring range
 -50 to +1700 °C


Humidity - Capacitive

Measuring range
0 to 100 %RH
Resolution 0.1 %RH (-50 to +150 °C)
Accuracy see probe data


General Technical Data
Weight 255 g
215 x 68 x 47 mm
Operating temperature  0 to +50 °C
Product-/housing material ABS 
Battery type 9V block battery
Battery life 45 h
Battery feature The hour times are reduced by a factor of 5 if a 9V rech. battery is used
Number of channels 2-channel
Storage temperature  -20 to +70 °C
Display type LCD
Display size 4 lines

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