Brochure

11
The triple point of water
(balance of all 3 physical
states solid, liquid and
gas) is used to repre-
sent the International
Temperature Scale and
for the highest precision
of temperature measure-
ments in the milli-Kelvin
range.
Incidentally, each precise humidity meas-
urement requires a parallel temperature
measurement. Only by using this method
are you guaranteed the best possible re-
sults.
Air Temperature No rules without
exceptions: in certain cases a combined
temperature/humidity sensor makes little
sense. This especially applies to refriger-
ators with extremely low temperatures.
Such ranges require various sensor de-
signs with the smallest possible diameter
in order to acquire precise temperature
measurements. Take for instance the
PT100 Sensors with a measuring range of
up to -100 °C.
Air Flow is one of the parameters
that needs to be monitored – especially
in highly sterile  lling processes (the so-
called Zone A). The Good Manufacturing
Practices (GMP) rules released by the FDA
state that air  ow speed has to be 0.45 m/s
± 20 % in any area.
Differential Pressure A minimal
amount of excess pressure is used when
working in sterile environments such as
in hospital operating theatres or in clean
room applications. By means of excess
pressure it is, to some extent, possible
to separate up to 3 or 4 different internal
levels by their particles.
The trick to this process is to keep the dif-
ferential pressure as low as possible. As a
result the requirements for the recording
equipment (transmitter) are very high: in
addition to a very good long-term stabi lity,
the transmitters have to be precise and
able to detect the smallest  uctuations in
values, because even a minimal devi ation
of the transmitter can cause problems
with the alarm process. Since differential
pressure is always meas ured against a
reference norm (the so-called “zero point”
– normally the pressure around the pro-
duction room), sensors with displays are
mostly used in order to make the zero-
point adjustment easier.
Particles In pharmaceutical manufac-
turing, for example, equipment is mounted
in the  lling areas that sucks all particles
by means of a pump and transfers these
to the actual measuring unit. Here, the
particles are put through particle sensors
which numerically measure and regis-
ter the size of the particles for a de ned
period of time.
While the pharmaceutical industry typ ically
distinguishes between particles of 0.5 to
5 micrometres, the requirements in the
semiconductor industry are con siderably
higher. Here, particles sizes of 0.3 to 0.5
micrometres are detected.
CO
2
In the research areas of the pharma-
ceutical industry and in universities, the
internal conditions of the human body
are simulated in incubators. In addition
to the 37 °C ambient temperature and
the relative humidity of more than 90 %
there is a high concentration of CO
2
. This
concentration is between 5 % and 10 %.
In comparison: in normal indoor air appli-
cations the CO
2
concentration, measured
in ppm (Parts per Million), is usually under
1,000 ppm, or rather 0.1 % CO
2
. In school
classrooms these values can be up to
3,000 ppm, which can lead to concentra-
tion disorders.
Sensors that are placed in incubators
should have long-term stability and be
easy to check on site by using a calibra-
tion standard.
Measuring is not just measuring.
Each application and application
area requires the ideal sensor.
Apart from this, it is imperative
in the pharmaceutical produc-
tion and food industry that the
hundreds of guidelines in place
are adhered to and a multitude of
inspections conducted. Only then
can long-lasting international
standards be guaranteed. Lufft
can help you fulfi l all such criteria
and fi nd the right product.
Humidity Measurements
Special
measuring conditions require special sen-
sors. In most cases only stainless steel
sensors are permitted in clean rooms.
Ideally, these sensors have corrosive free
connector inserts between the elec tronics
and sensor head. On the other hand, in
explosion-proof areas a sensor with a
specially designed power supply is applic-
able: in this “zone-zero application” the
electronics for the transmitter are mostly
mounted outside the critical area.
Normal humidity measuring in a clean
room essentially provides sensors with a
“stress-free climate” as opposed to “long-
term stability tests” where equipment
is tested under tropical conditions. It is
important, however, to complete a basic
calibration of the sensors on site and if
necessary, carry out the unproblematic re-
placement of equipment.