Testo 6781 Data sheet

Trace Humidity Monitoring up to -90 °C

td

testo 6781

Committing to the future

New, condensation-proof sensor with sol-gel technology

Highest compressed air quality requirements

2

Monitor trace humidity, avoid damage

Air, compressed air and gases are used in all
areas of industry. Humidity is normally
undesirable because it can cause damage or
impair the quality of the end product, as the
adjacent graphic shows.

Optimizing the regulation of adsorption
dryers

The regeneration cycle can be reduced by
controlling the parameter trace humidity
(°C

td

). That saves energy costs!

Gas engineering: humidity
causes damage and reduces
the value of the gas in the
system

Granulate drying: dry air is a
requirement for product quality

Medical compressed air:
minimum humidity as a hygiene
requirement

Compressed air systems: dryer
monitoring to avoid damage
caused by humidity

Trace humidity monitoring with testo 6781 avoids follow-on
damage caused by humidity

>>

Manufacture Distribution Consumer

Corrosion in pipes
and components

Pneumatic drives:
– Interrupted lubrication
– Mechanical damage

Formation of ice in
outside and low-

Compressor

Dryer

e.g. medical
compressed
air

Damp powder
sticks together

Bacterial growth
(European drug
legislation)

e.g. transport air for
pharma. powder

ISO 8573

Action Compressed air drying

testo 6781

Monitoring/controlling

Class

1

2

3

4

5

6

7

-70

-40

-20

3

7

10

–

-94

-40

-4

37

44

50

–

0,003

0,12

0,88

5,51

7,28

8,93

–

0,37

18

147

1083

1432

1756

–

Semi-conductor prod.

Granule dryer

Transport air

Working/energy air

Blow air

°C

td

°F

td

g/m

3

ppm

v

(at 7 bar)

Trace humidity Typical application

Applications in the monitoring of compressed air quality

What is compressed air quality?

The international standard ISO 8573 defines
seven classes of compressed air quality and
defines the humidity, the oil content, the
particle content etc. which the compressed
air is allowed to have. Class 1 represents the
highest requirements. Class 2, for example, is
fulfilled when the pressure dewpoint does not
exceed -40 °C

td

or -40 °Ftd, or an absolute

humidity of 0.12 g of water vapour per m

3

or

18 ppm

V

(parts per million by volume) (see
table on right).
The main way of ensuring compliance with a
quality class involves installing a suitable dryer
e. adsorption dryer). Its monitoring and,
where appropriate, its control, is handled by
the testo 6781.