Measurement principle

The Viscomat works on the capillary principle, which is the most exact method for the determination of the viscosity. The time, which is necessary for a defined volume of a liquid to pass throw a capillary at a known differential and defined temperature is measured. A determination of the density is not necessary. Therewith the Viscomat allows a direct measurement of the dynamic viscosity. The resulting viscosity is indicated in millipascal-seconds (mPas).

The Viscomat is optimized for the use in breweries and malt houses. The results of beer and wort samples are converted automatically to a fixed original wort and extract content, if the original wort and extract contents of the samples had been entered before.

After having filled the sample plate and activated the measurement the Viscomat carries out the complete analysis without any intervention of the operator. The instrument carries out the feeding of the samples, the temperature equalization, the measurement process, the cleaning and the calibration fully automatically.

By means of a vacuum pump a vacuum is created inside the collecting vessel by means of the vacuum tank. The vacuum tank is used for the buffering and elimination of pressure fluctuations. The hollow needle of the sampler dips into the sample and takes a certain volume of the liquid from a programmed position of the sample plate. The sampling is controlled by the light barrier L3. The liquid to be measured reaches the measurement chamber. The liquid is tempered to +20°C (± 0,05°C) inside a pre-chamber by means of a thermoelectric cooling and heating device. Then it passes through the capillary. The time, which is necessary for the volume, which is limited by means of the light barriers L1 and L2, to pass through the capillary is measured and used for the calculation of the viscosity. The manometer measures the differential at the capillary for the determination of the viscosity.

The operation of the Viscomat is menu-driven. The operator chooses the requested function by means of the selection menues. Two operational modes are integrated: one user mode for the daily work and one expert mode for the individual modification of measurement parameters. The keypad allows an easy operation of the instrument. The measurement results, the status of the measurement, the measurement parameters, etc. are clearly indicated on the large and illuminated display.

The sample plate is filled with the samples to be measured. The operator chooses the sample type in the menu "measure" and enters the sample positions into the sampler. The measurement cycle is activated by means of the "Start" key. After each sample the Viscomat prints the results according to the requested output possibility.

To increase the measurement safety each sample can be measured several times. The mean value is taken automatically from the single values. All measurement values, which exceed a limit value preset by the operator are recognized as runaways and are not considered in the mean value. The number of repeated measurements can be preset by the user or can be determined automatically by the Viscomat.

The Viscomat is equipped with various output possibilities of the measurement results. A documentation of the results by means of the built-in thermoprinter is possible. The results can also be stored on disk as ASCII-text file or transmitted to a PC by means of the serial interface. Furthermore the results can be printed on an external printer by means of the parallel interface.

Especially in case of a large number of samples a manual feeding of the liquids before each measurement is time-consuming and expensive. The Viscomat is equipped with a sampler, which allows the fully automatic measurement of up to 25 different samples during one measuring cycle. Each sample container has a capacity of 6 ml liquid, which is sufficient for up to 4 measurements.

The instrument is cleaned with destilled water and a cleansing liquor, preferably acetone. They are filled into the big containers positioned at the left side of the sample plate. Four rinsing programmes are implemented. Two programmes are necessary for the automatic intermediate cleaning before each new sample and each new single measurement. A further programme is carried out after the complete series of measurements, which is very important in order to avoid the drying in of sample residues inside the capillary. The fourth programme serves as main cleaning of the system and can be carried out on request. The parameters for all rinsing programmes can be set individually by the operator.

In order to guarantee a troublefree measurement the samples to be measured must be decarbonized. This can be made by means of the built-in vacuum decarbonization device of the Viscomat, which allows an easy decarbonization of the beer samples. For this purpose the operator selects the menu "decarbonize", fills the sample into an Erlenmeyer flask and closes the flask with the stopper of the decarbonization device.

For the calibration of the Viscomat preferably destilled water with 1,002 mPas is used. Other reference liquids of known viscosity, like e.g. 20% saccharose-solution with 1,96 mPas can also be used. The operator selects the item "calibrate", places the sample container with the standard into position no. 25 of the sample plate and starts the calibration. The Viscomat measures the flow rate for the standard in milliseconds and stores this value. All following viscosity measurements will use this value for the calculation of the viscosities.

Setting of parameters

The Viscomat offers a large number of different parameters which can be set individually by the operator. In order to avoid an unintentional misadjustment of the parameters, the operator must change from the "user mode" to the "expert mode" in order to change the settings. The measurement parameters like temperature, differential, number of measurements per sample and error tolerance can be set in the menu "extras" and other subordinated menues. Furthermore the parameters for the rinsing programmes, for the documentation of the measurement values and for the interfaces can be set.

The instrument is equipped with a PC for the control of all processes and for the calculations. The modular construction of the Viscomat guarantees a high ease of servicing.