Early varicap diodes usually required a reverse voltage range of 0 & ndash; 33 v to obtain capacitance range, which was quite small, approximately 1 & ndash; 10 pF . These types were and are still extensively used in television tuners, whose high carrier frequencies require only small changes in capacitance.
42.
For tantalum capacitors a DC bias voltage of 1.1 to 1.5 V for types with a rated voltage of d " 2, 5 V or 2.1 to 2.5 V for types with a rated voltage of > 2.5 V may be applied during the measurement to avoid reverse voltage.
43.
The standardized measuring condition for e-caps is an AC measuring method with 0.5 V at a frequency of 100 / 120 Hz and a temperature of 20 �C . For tantalum capacitors a DC bias voltage of 1.1 to 1.5 V for types with a rated voltage d " 2.5 V, or 2.1 to 2.5 V for types with a rated voltage of > 2.5 V, may be applied during the measurement to avoid reverse voltage.
44.
The standardized measuring condition for polymer Al-e-caps is an AC measuring method with 0.5 V at a frequency of 100 / 120 Hz and a temperature of 20 �C . For polymer Ta-e-caps a DC bias voltage of 1.1 to 1.5 V for types with a rated voltage d " 2.5 V, or 2.1 to 2.5 V for types with a rated voltage of > 2.5 V, may be applied during the measurement to avoid reverse voltage.
45.
A number of adaptations were needed to make such valves suitable for HVDC, in particular the use of anode voltage grading electrodes to minimise the risk of " arc-back " at the very high reverse voltages experienced in HVDC . Much of the pioneering work in this area was performed in Sweden by Dr Uno Lamm, widely considered the Father of HVDC and in whose name the IEEE introduced the Uno Lamm Award for outstanding contributions in the field of HVDC . The very long anode columns needed for high voltage applications limited the current which could safely be carried by each anode, so most mercury-arc valves for HVDC used several ( most often, four ) anode columns in parallel per valve.
