Periods Without Operation; Reproducibility Of Results; Viscometers Within Quality Assurance Systems - Fisher AVS 470 Manual De Instrucciones

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Chapter 6 Maintenance and care of the AVS 470 Viscosity Measuring Unit and the viscometers
6.4

Periods without operation

If the capillary viscometers are not used over a long period of time, the liquids contained in the system, in
particular aggressive solutions, have to be drained. If the liquid is left in the system, one has to reckon that
the solutions used will alter in the course of time and attack the glass, in particular the capillaries. Cleaning:
It is recommended to use 15% H
appropriate solvent. It has to be perfectly dry and dust-free, thereafter it is suitable for manual and automatic
measurements.
6.5

Reproducibility of results

The measurement or analysis results depend on a variety of factors. Please check the plausibility of the
measurement results or analysis results at regular intervals, and carry out the required reliability tests. In this
regard, please adhere to the usual validation procedures and especially to the "Viscometers within quality
assurance systems" chapter.
6.6

Viscometers within quality assurance systems

Recommendations for companies that have introduced a quality assurance system in accordance with the DIN EN
ISO 9001 standards. In this quality assurance system, an inspection of the measuring equipment is planned. The
intervals and required accuracy can be defined by each company according to its own requirements. The standard
DIN/ISO 10 012, Part 1 serves as a guideline in this matter. We recommend regular inspection of the viscometers in
defined intervals.
Inspection of the viscometer constants:
1. Calibration using comparative measurements with reference measuring standards
Comparative measurements must be performed with a viscometer (reference measuring standard) which was
tested at the PTB (Federal German Physical-Technical Institute) and provided with a constant. During this
comparative measurement, the viscometer to be inspected and the PTB - tested viscometer were placed simultane-
ously in the same thermostat bath. The test liquid tested, the viscosity of which must not be known exactly, is filled
into both viscometers, tempered and the flow-through time then measured. The constants of the viscometers to be
inspected are then calculated according to the following equation:
⋅
K t
Uref Uref
K =
t
K = constant of the tested viscometer
K = constant of the standard reference viscometer
Uref
t = low time (HC) of the tested viscometer (corrected by Hagenbach-Couette)
t = flow time (HC) of the standard reference viscometer (corrected by Hagenbach-Couette)
Uref
Within the quality assurance system in accordance with DIN EN ISO 9001, traceability of the measuring equipment
to national measuring standards is demanded. This traceability can be achieved by inspecting the comparative
viscometers (reference measuring standards) at regular intervals at the PTB. The time intervals are defined
according to the specifications made in the quality assurance system of the user.
2. Calibration of the capillary viscometer with normal oils of the PTB
During this calibration, a normal oil from the PTB with known viscosity is used as a reference measuring standard.
The measurement is performed by means of flow-through measurement of the PTB normal oil in the viscometer to
be inspected in a temperature bath, the temperature of which must correspond precisely to the test temperature of
the PTB. In this case, it is extremely important to make sure that the temperature is absolutely correct. In case of
temperature variation, this will always result in a constant for the viscometer that deviates from the constant applied.
A temperature variation of 0.01 K, for instance, will result in a measuring error of up to 0.01 %. The calibration of the
deviating temperature into the viscometer constant is not permitted.
3. Inspection by Schott Instruments with quality certificates in accordance with DIN 55 350-18-4.2.2
The inspection at Schott Instruments is carried out by means of comparative measurements using viscometers as
reference measuring standards that were tested at the PTB (corresponds to Item 1).
Information on the stability of viscometer constants
Each inspection (even with a certificate) can guarantee the technical measuring direction only for a limited period of
time. The constants of viscometers made of the borosilicate glass DURAN
long periods of time if the viscometers are kept away from altered influences. Especially extreme changes can be
expected, for instance, during the use of liquids that attack glass, in particular hot caustic soda hydrated (NaOH) or
during glass-blowing repairs (even for apparently insignificant repairs).
O and 15% HCl for cleaning. Subsequently, rinse the viscometer with an
2 2
®
, however, can remain unchanged for