Four-terminal-pair networks as precision admittance and impedance standards

Techniques for comparing four-terminal-pair admittance standards

“…Some prope rti es of four-pair admittance s tandard s which make them parti c ularly useful are their relative insensitivities to variation s in series impedan ces and shunt admittances in th e leads as is implicit in (2), and the fac t that standards of either very small or very large admittance may be constructed in suc h a way that their four-pair admittances are nearl y ide ntical with th eir ordinary two-pair admittances obtained by eith e r open circuiting or short circuiting th e two extra terminal pairs . These properties are discussed in th e referen ce cited above [1].…”

“…These seven adjustments are required only for realizing the defining conditions for the four-pair admittances, and may be un calibrated. The eighth complex adjustment required to balance the bridge is made through the use of two seven-dial inductive voltage dividers Tz and T3 , which drive small fixed capacitors labeled Yo and If we represent the ratio of T4 by eb = -ell (l + 0) with 0 complex and I 8 I ~ 1, and since ed = ea (2k l - 1) and ef = -eb(2k2-1) , we have the balance condition…”

“…A theor eti cal justification of thi s co mposite sys te m in whic h the s tan da rd s are provid ed with four p airs of terminals was published in 1964 [1] I, but with the excepti on of a paper by Homan [2] which was limited to m eas urements on fairly small impedances, no sys tematic investigation of four-pair admittan ce meas ure ments has ye t been described. Th e process of convertin g to fourpair m eas urement syste ms has been underway a t th e National Bureau of Standards for several years, durin g which time many of the special proble ms involve d in th eir use have been investi gated.…”

“…Th e equivalent circ uit of a four-pair a dmittan ce standard is shown in fi gure l a, take n from th e p aper cited above [1], and in an abbreviated form , in fi gure lb. The standard may be vi ewed as a device in whi c h th e ratio of c urrent in pair 3 to the open circ uit voltage at pair 2, subject to the condition that both the voltage and c urre nt at pair 4 are zero, is the parameter of inte rest.…”

Some techniques for measuring small mutual inductances

“…Thus relative motion between the primary and secondary windings could change the inductance. A calculation for the 0.1 /LH inductor indicates that such a net loop of 1 mm 2 would dictate that for stability of one part in 10 8 , the relative motion of primary to secondary must be 10- 5 mm.…”