Precision automated capacitance bridges for the low frequency range at the PTB

Two computer-controlled capacitance bridges for different fields of application have been developed at the PTB. The first one, the universal bridge, works in the capacitance range of less than 1 pF up to 1 /spl mu/F and in a frequency range up to 1 kHz, The total calculated relative uncertainties (2/spl sigma/) are in the order of 5/spl middot/10/sup -6/ and 20/spl middot/10/sup -6/. The second one, the fixed ratio bridge, calibrates primary standards with capacitance values from 1 pF to 1 nF in 1:1, 1:2, 1:5 or 1:10 steps at frequencies from 100 Hz to 10 kHz. The relative uncertainty of one 1:10 step at a frequency of 1592 Hz is estimated to be 3/spl middot/10/sup -8/ (1/spl sigma/).<>