Electrical Impedance

106 Electrical impedance: principles, measurement, and applications

P

1

/P

2

= k

−1

. The power ratio is the electrical dissipation of resistors R

1

and

R

2

under comparison. Since the maximum measurement power is determined

by the standards’ specifications (often P =1 mW for medium-valued resistance

standards), for large k one of the standards is excited with too low electrical

power, and bridge sensitivity is compromised.

R

2

R

1

I

2

I

1

DG

V

2

V

1

n

2

n

1

n

2

n

1

Figure 4.14

A 2T equal power ratio bridge, having ratio (n

1

/n

2

)

2

.

The equal-power transformer ratio bridge (Blumlein, 1940; Hall, 1970),

Fig. 4.14, is a combination of a voltage ratio and a current ratio bridge. If

both ...