COSA Xentaur Hygrocontrol Type 72 - Manual (Page 10)

Series 72 Manual page 6
F) = sensor oscillator
R) = reference oscillator
Finally the display shows the actual pressure factor, marked by "PRESS". This
factor is used to calculate humidity values at atmospheric pressures, if
measurement occurs at other pressure conditions.
The calibration data display may be left by pressing "E", the program then
jumps back to "CALDAT".
6.Calibration
6.1. General Notes about Calibration Standards
There is a lack of international standards for rel. Humidity calibrations,
therefore, different countries may have different methods of calibrations. Since
the users of humidity meters need a simple method to check the accuracy of
their instruments, we are supplying accessories for calibration or testing. As a
standard method we have chosen unsaturated salt solutions to create rel.
humidities of known amount - but saturated salt solutions may also be used.
Series 72 instruments are to be calibrated with rel. humidity - since their
sensors respond to relative, not to absolute, humidity values.
6.2. How often Calibrations should be done
Before dispatch, all probes have been calibrated at 0, 20, 35, 50, 65, 80 and
95%. Changes of sensor characteristic are hard to predict, as they depend on
mechanical and chemical attack on the probe. If stresses are high (such as
temperature, vibration, dust and aggressive media like acids, solvents and
highly reactive gases), we recommend a test within 3 to 12 months. If deviations
of more than 2% are found, a recalibration makes sense.
In some cases, when the humidity range the probe has to detect is a narrow
one - then a partial calibration may be helpful. If you want the best accuracy
over the total range (from 0 to 100%), then as many points as possible should
be used for calibration.
6.3. Salt Solutions for Calibration
The solutions we supply for calibration create rel. humidities from 0 to 95%. We
are using the following:
0% - drying granulate
10% - mixed LiCl and ZnCl2 solution
20, 35, 50, 65, 80, 95% - unsaturated LiCl solutions
The marked rel. humidities relate to a temperature of 22°C and do have a
temperature dependency. The accuracy of the solutions at 22°C is +/- 0.5%,
they are not toxic and are not dangerous to the environment.