Page 469 - Instrumentation Reference Book 3E

452 Electrical measurements

rectification @Zt.
Half-wave
\L
Vout

R Vi n

Vin Figure 20.32 A.c.signal
precision rectification.

Multiplier I Low-Pass ' Square-root
filter extractor

Under steady-state conditions

Figure 20.33 (a) RMS evaluation by
analog multiplication; (b) a.c./d.c.
(b) conversion using thermal techniques.
20.4 Power measurement then i(t) must be of the form

For a two-terminal passive network if the instant- i(t) =i sin (ut + 4)
aneous voltage across the network is v(t) and the
instantaneous current through it is i(t) then and the instankmeous Power, P(t). is given by
the instantaneous power, p(t), taken or returned p(t) = v(t) i(t) = i-i sin wt sin (wt + 4)
to the source is given by
The average power dissipated by the network is
p(t) = v(t) . i(t)
given by
For a linear network, if v(t) is sinusoidal, i.e.,