60
Application report
Wissenschaftlich-Technische Werkstätten GmbH
Control of conductivity systems acc. to ISO
9000; GLP - requirements
Replaces reports 53023,
293054, 594054 and 994054
As part of the introduction of a quality system according to
standard series DIN ISO 9000, a growing number of users find
themselves obliged to carry out test equipment checks for the
measuring systems applied. In this context, the system of rules of
the GLP (Good Laboratory Practice) results in almost identical
requirements.
To enable you to meet the ISO 9000 and GLP requirements, it is
necessary to establish the following conditions:
- The measuring systems applied must be calibrated at regular
intervals in order to ensure the accuracy and comparability of the
measuring data acquired.
- The completion of the specified calibrations must always be
recorded in writing: type and identity number of measuring
instrument and measuring cell, date, signature of the person
carrying out the calibration.
It is advisable to have a separate log form or log book for each
measuring system (instrument with measuring cell) where the
calibrations are entered consecutively. This documentation should
also state the calibration intervals, so that the user can see at any
time when the next calibration is due.
Consequently, it will no longer be necessary to attach calibration
labels on the instrument and the measuring cell.
No.: LF 1194054
LF 1194054
82362 Weilheim
•
Dr.-Karl-Slevogt-Str. 1
Tel (0881) 183-0
•
Ttx 881 803
•
Fax (0881) 6 25 39
Directors: Wolfgang Bohn, Klaus Rommel
61
LF 1194054
- Calibration intervals and instructions for carrying out calibrations are to be
specified in writing:
The appropriate calibration interval depends on the conditions of application
and must be fixed by the operator on his own responsibility according to his
experience.
The procedure for carrying out the calibration is laid down in standard EN
27888. It is therefore sufficient to refer to this standard as instructions for
calibration.
If desired, we can also check the instrument and measuring cell for you at
our works and issue a corresponding test certificate. You will nevertheless
still need to carry out regular calibration.
Calibration
Standard solutions
Use potassium chloride solutions according to the specifications of
standard EN 27888
Concentration
Conductivity at 25°C
in mol/l
in mS/m
µS/cm
0,0005
7,4
74
0,001
14,7
147
0,005
72
720
0,01
141
1413
0,02
277
2770
0,05
670
6700
0,1
1290
12900
0,2
2480
24800
Disturbing gases in water for preparing potassium chloride solutions
with concentrations c < 0.01 mol/l must be removed by degasing the
water with nitrogen or heating it up. The conductivity should be less than
2 µS/cm. The solutions have to be freshly prepared before use.
Solutions with low potassium chloride concentrations (c < 0.01 mol/l) are
very unstable. During calibration one can expect larger deviations of the
measured values from the theoretical values.
