Page 446 - Instrumentation Reference Book 3E

Units and standards of electrical measurement 429

Table 20.2 UK rf and microwave standards (from Steele et a!. 1975)
Quantity Method Frequency Level Uncertainty
(GW (95 % confidetux)
-
Power in 14mm coaxial Twin calorimeter 0-8.5 10-1 00 mW 0.2-0.5%
line
Power in 7 mm coaxial Twin calorimeter 0-1 8 10-100 mW Under
line development
Power in W616 (WR90) Microcalorimeter 9.0, 10.0. 12.4 1 0- 1 00 mW 0 2%)
Power in W6l8 (WR62) Microcalorimeter 13.5, 15.0, 17.5 10-1 00 mW 0.2%
Power in W622 (WR28) Microcalorimeter 35 IO-lOOmW 0.5%
Power in W626 (WR12) Twin calorimeter 70 lOmw 0.8%
Attenuation w.b.c.0. piston 0.0306 0-120 dB 0.002 dB
Attenuation in 14 mm w.b.c.0. piston 0-8.5 0-80 dB 0.001 dB/iOdB
coaxial line
Attenuation in
WGllA (WR229) Froin 0.002 dB
WG15 (WRl12) at low values
WGI6 (WR90) Modulated 0-100dB up to 0.02dB
WG18 (WR62) sub carrier at 100dB, for
WG22 (WR28) v.s.w.r. < 1.05
WG26 (2512)

Impedance
Lumped conductance rf bridge 1 10-3 10pS-IS 0.1Y"
Lumped capacitance rf bridge 1 x 10-3 1 pF-IOpF 0.1%
Coaxial conductance Woods bridge 5 x 10-3-30 x 10-3 040mS 0.1% A 0.001 ills
30 x 10-'-200 x IO-' 0.2% i 0.001 mS
Coaxial capacitance Woods bridge 5 x 10-3 040 pF 0.1% + 0.001 pF
(these refer to major components only)
K
Noise temperature
in 14mnn coaxial line Thermal 1-2 104
in WGID (WR284) Thermal 2.75, 3.0, 3.5 104 About l.5K
in WGI4 (WR137) Thermal 6.0, 7.0. 8.0 1 04 transfer
in WG16 (WR90) Thermal 9.0, 10.0, 11.2 104 standards
in WGlX (WR62) Thermal 13.5, 15.0 104 calibrate to
in WG22 (WR28) Thermal 35 104 110K
in WG11A (WR229) Cryogenic 17 0.15 K: transfer
in WG15 (WRI12) Cryogenic I7 standards
calibrate to 0.6 K

Lampard 1956). This capacitor has a value which
can be determined from a knowledge of the vel-
ocity of light and a single length measurement.
A-seai ing the symmetrical cross-section shown in Figure
Seal Consider a cylindrical electrode structure hav
20.7(a) in which neighboring electrodes are separ-
ated only by small gaps; Thompson and Lampard
showed that the cross capacitances per unit length
C, and C, are related by

sulphate crystals
sulphate crystals Because of symmetry C1 = C, and the cross-
Cadmium amalgam :apacitance per meter, C, is given by
EO log, 2
+ve -ve C=- F/m
Figure 20.3 Weston standard cell. 7T