Reproducibility Of Results; Viscometers Within Quality Assurance Systems - Xylem SI Analytics AVS 370 Manual De Instrucciones

Strong oxidizing cleaning agents such as chromic acid may only be used by trained
personnel and must be suitably disposed for safety and environmental reasons - the current
guidelines for handling hazardous materials must be observed.
In the last rinse cycle, the viscometer should be rinsed with a suitable solvent with a low boiling
point (such as acetone), and dried by an air flow, which is preferably generated by underpressure
(for example, water jet pump). The viscometer is dry and dust-free by this treatment and can thus be
used for manual and automatic measurements.
5.4

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.
5.5

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:
a) 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 simultaneously 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 constant of the tested viscometer
K constant of the standard reference viscometer
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)
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.
b) 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.
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