5.5.1 Halogen leak detectors
(HLD 4000, D-Tek)
Gaseous chemical compounds whose molecules contain chlorine and/or
fluorine – such as refrigerants R12, R22 and R134a – will influence the
emissions of alkali ions from a surface impregnated with a mixture of KOH
and Iron(III)hydroxide and maintained at 800 °C to 900 °C by an external
Pt heater. The released ions flow to a cathode where the ion current is
measured and then amplified (halogen diode principle). This effect is so
great that partial pressures for halogens can be measured down to
10-7 mbar.
Whereas such devices were used in the past for leak testing in accordance
with the vacuum method, today – because of the problems associated with
the CFCs – more sniffer units are being built. The attainable detection limit
is about 1 · 10-6 mbar · l/s for all the devisces. Equipment operating in
accordance with the halogen diode principle can also detect SF6.
Consequently these sniffer units are used to determine whether refrigerants
are escaping from a refrigeration unit or from an SF6 type switch box (filled
with arc suppression gas).
5.5.2