1. GIS SF6 Gas Insulated High Voltage Switchgears and Solution Control, ABB documentation, Zürich, Switzerland, 1995.
2. Standard Products 99, Trafag Sensors and Control, Männedorf, Switzerland.
3. Digiquartz 2200 data sheet, Paroscientific FS, Redmond, WA.
4. Survey of quartz bulk resonator sensor technologies;Eernisse;IEEE Trans. Ultrason. Ferroelectr. Freq. Control,1988
5. H. Brändle, W. Gribi, K.-Y. Haffner, Device for measuring gas density, US Patent 5,421,190 (1995).