Pressure measurement

Table of Contents

Similar to temperature, pressure can also be measured via external sensors in reference vessels.  However, the high risk of contamination or leakage creates a major disadvantage, so that a non-contact pressure measurement, as shown, is preferable.

A method that enables pressure measurement in all decomposition vessels is based on the stress-optical behavior of a glass ring that is firmly integrated as a sensor element in the lid of the decomposition vessel.

When pressure is applied, the oscillation plane of the irradiated light is rotated, which is proportional to the internal pressure. This rotation is measured in a subsequent analyzer, which the pressure is calculated from. The sensor element, which is made of glass, is firmly integrated into the lid so that the handling of the vessels is not affected by the pressure measurement and no additional work steps are necessary.

The optical system determines the pressure in all containers simultaneously with the temperature measurement described above. The pressure-time curve is displayed and stored separately on the controller for all vessels. The accuracy of the method is 5 bar over the entire measuring range of 0-120 bar, which is more than sufficient for controlling digestion processes.

Microwave power control

As long as the measured pressures stay below a preset maximum value, the microwave is solely controlled based on its temperature. However, as the vessel approaches the maximum allowable pressure, the system will down-regulate the microwave power. Organic sample material produces a lot of CO2 during digestion, which leads to an increase in pressure. In order to allow the sample to react slowly and safely, the microwave power is reduced. In the event of a large increase in pressure, a corresponding reduction in temperature is accepted.