With the application of pressure dew point regulator IDPC 40, it is possible to use the first
alarm contact for regulation of dryers. Hence, the air is dried only so much, which is
necessary for the process and the operating costs are substantially reduced. The period of
regeneration interval, when flushing air is used, is adapted as per the desired dew point
value at the air outlet of dryer. Therefore, with partial load the energy consumption is much
lower without which the humidity content of compressed air gets worse. With no load, the
self-air consumption of the dryer is almost zero, with which the operating costs is
substantially reduced. The service life of the column also increases, which results in another
savings in maintenance costs.
The second alarm contact can be additionally used for alarm signal. Hence, a shut-down of
the dryer on overload can be detected and safety measures can be timely introduced.
17
Checking the measuring accuracy
The measuring accuracy of the humidity probes can be checked up to a range of -5° C dtp
with the help of salt reference cells available as accessories. Lithium Chloride cell is suitable
for cross checking in this measuring range. Further information can be obtained on request.
The cross checking of the lower measuring range of up to -30°C is only possible at
manufacturer's works in a calibration facility. We recommend re-calibration in a cycle of 12
months.
18
Working principle
For technically interested users, there is some further information about the procedures and
measuring accuracy of the products:
The capacitive polymer sensor used in the measuring probe measures the relative humidity
and a precision NTC measures the temperature. From these two parameters, the (pressure)
dew point is calculated with high accuracy with the help of water vapour saturation
characteristics stored in the micro-controller.
The vapour pressure saturation characteristics are natural characteristics, which runs non-
linear. At higher temperature differences between dew point and ambient temperature, the
precision requirements are very high for measurement of relative humidity and it is
necessary to calculate a sufficiently accurate dew point value for the process. The measuring
accuracy requirements become more stringent with increase in application temperature band
towards higher temperatures.
Since the process temperature is normally quite higher than the dew point temperature
which can be measured, it results into a measuring band within the lower range of relative
humidity. The following table is used for explanation:
