testo 635-1 - Humidity measuring instrument

Order-Nr.  0560 6351

This meter uses a sensor to start up. Click here for probe selection.
  • Probes available as an option mean you can measure air humidity, temperature, absolute pressure, and dew point in compressed air

  • Measures air moisture, material equilibrium moisture, pressure dew point

  • Calculates dew point and dew point distance

  • Cyclical printing of readings once a minute, for example

The testo 635-1 temperature and humidity measuring instrument enables you to measure the temperature, air humidity, and dew point – in compressed air as well. State of the art technology and a large selection of probes, which are available optionally, allow for a wide variety of measuring possibilities.


Product Description

The testo 635-1 is for measuring air moisture, material equilibrium moisture, and pressure dew point in compressed air systems. Up to 3 temperature or humidity probes can be displayed; data transmission is radio-controlled, or wireless. Measurement data can be transmitted by infrared to the Testo printer. It is also possible, during cyclical printing, to print measurement data once every minute, for example.
The testo 635-1 immediately displays the dew point difference between ambient air and the wall surface, when analyzing moisture on walls and ceilings.
There are precision probes up to -60°C tpd available to inspect pressure dewpoint in compressed air systems. The humidity sensor developed by Testo has proven itself world-wide and has outstanding features in terms of precision, long-term stability, temperature resistance and robustness.

Delivery Scope

testo 635-1 temperature and humidity measuring instrument, including calibration protocol and batteries
Caution: The instrument can only be commissioned with a probe. These are available separately.

Technical Data

Temperature - NTC

Measuring range

-40° to 302 °F / -40 to +150 °C


±0.4 °F (-13° to 166.8 °F) / ±0.2 °C (-25 to +74.9 °C)

±0.7 °F (-40° to -13.2 °F) / ±0.4 °C (-40 to -25.1 °C)

±0.7 °F (167° to 211.8 °F) / ±0.4 °C (+75 to +99.9 °C)

±0.5 % of mv (Remaining Range)


0.1 °F / 0.1 °C

Temperature - Type K TC

Measuring range

-328.0° to 2498 °F / -200 to +1370 °C


±0.5 °F (-76° to 140 °F) / ±0.3 °C (-60 to +60 °C)

±(0.4 °F + 0.5 % of mv) (Remaining Range) / ±(0.2 °C + 0.5 % of mv) (Remaining Range)


0.1 °F / 0.1 °C

Humidity - Capacitive

Measuring range

0 to +100 %rH


See probe data


0.1 %rH

Absolute Pressure

Measuring range

0.0 hPa to +800.0 InH₂O / 0 to 2000 hPa


See probe data


0.0 InH₂O / 0.1 hPa

General technical data


15 oz. / 428 g


9 x 3 x 2 in. / 220 x 74 x 46 mm

Operating temperature

-4° to 122 °F / -20 to +50 °C


ABS / TPE / Metal

Battery type

Alkaline, type AA

Battery life

200 h

Storage temperature

-22° to 158 °F / -30 to +70 °C


Air Probes

Pressure Probe Accessories

Absolute pressure probe 29 psi

Order Number: 0638 1835

RFID Probe

Humidity probe head

Order Number: 0636 9736

Surface probes



$ 163.00
excl. tax


Localising mould

Damp ceilings and walls may be a result of structural damage. In most cases, however, it is a sign of improper ventilation. Once the mould appears inside a house, the tenant assumes that moisture has come in from outside. Numerous disputes have erupted because of the issue of who is liable for the mould damage. However, it is difficult to find out who or what has caused the mould: the tenant or faulty structural design?

Testo 635-1 is ideal for measuring moisture in ceilings and walls. Using the optional attachment temperature/moisture probe and optional surface temperature probe, the testo 635 automatically calculates the dew point distance. It provides initial information about whether mould is being caused by condensation, or from moisture ingress due to structural damage or faulty insulation.

Monitoring production and storage conditions

Our temperature/humidity measuring instruments are used around the world in production, storage and server rooms, museums, archives, cold storage warehouses, containers and sales counters.

Manufacturers, carriers, or dealers of sensitive products must ensure that specified temperature or humidity values are observed during production and storage. The testo 635 offers the option of performing spot measurements in relevant places.

The temperature/humidity measuring instrument testo 635-2 offers the user a wide range of humidity/moisture probes. It provides the option of measuring humidity, material moisture and U-value (for the thermal assessment of structural components). In addition to the standard probes, up to three radio probes can be connected to the device in parallel. Measurement results can be analysed, stored and documented using the supplied PC software.


Product Brochures



This meter uses a sensor to start up. Click here for probe selection.