Page 119 - Mechanical Engineers' Handbook (Volume 2)

108 Bridge Transducers

ducer by moving the frequency content of a signal into some new range of the frequency
spectrum. This procedure is known as amplitude modulation. Reference 13 forms the basis
for the following discussion.
Referring to Fig. 28, amplitude modulation can eliminate paths 1 and 3 (noise) from
the net output signal. Thus, self-generating electromotive force (emf), such as thermoelectric
and electromagnetic ones, can be separated from emf attributable to resistance changes in a
bridge transducer.
A design procedure is presented for an ac-powered bridge where the signal input to the
self-generating response extends to frequency and the input to the non-self-generating
1
response extends to . Power supplied is at frequency . The design method developed
2 3
requires a knowledge of these frequencies. A procedure to determine these frequencies in-
volves the following:

Figure 30 Signal frequency contents, dc bridge. (Adapted with permission from ‘‘Information as a
‘Noise Suppression’ Method,’’ by Peter Stein, Stein Engineering Services, Inc., Phoeniz, AZ, LR/MSE
Publ. 66, 1975.)