When handling radioactive substances strict safety standards have to be met. In its "Hot Cells" department, the Karlsruhe Research Centre (Forschungszentrum) uses type TA thermal flow sensors for flow measurement made by Höntzsch in Waiblingen.

In specially screened, partially gastight manipulation boxes, samples contaminated with radioactivity are processed for material tests by using mechanical grippers. For cleansing purposes flammable solvents are also used.

The waste gas is decontaminated through several very fine filter sets and then blown out into the atmosphere. So that on the one hand the solvent concentration does not reach any significant values under which a deflagration could occur, and on the other hand so that the radiation level remains within the limit values, a certain flow rate with inert gas must be provided within the containment.

For the volume flow measurement required by the TÜV (technical monitoring authority) at the Karlsruhe Research Centre, a total of nine thermal sensors have been installed. They deliver the necessary measurement values which are transferred to a VT-TA evaluation unit. If the flow rate drops below a minimum value an optical warning signal is issued.

For the application described, high reliability and a long service life are essential. On account of this, the Karlsruhe Research Centre decided to use a sturdy low wear sensor with no moving parts.

As the dimensions of the type TA thermal flow sensors are small, they can also be used in smaller nominal widths. The loss of pressure resulting is negligible.

Thanks to the large measurement range of 1:250, a reliable measurement in a broad range of operating states is possible.

On the basis of the measurement principle, thermal flow sensors deliver the flow speed proportional to the mass without the need for pressure compensation. The operating temperature is measured and is available for further processing.

Thermal TA flow sensors are particularly suitable for measuring small speeds as they are most sensitive in this range.

In its thermal flow sensors product range, Höntzsch supplies sensors with a temperature resistance of up to +240 °C and a pressure resistance of up to 1 MPa/10 bar.