. Electronic apparatus for biological research . Frequency Figure Response of electrodynamic transducer for constant input displacement Graph 9 shows that there is an essential difference between electrodynamic and piezo-electric transducers, although both give no output at zero frequency. Electrodynamic transducers can be constructed with very low mechanical impedance, suitable for use for measuring displacement. However, the rising frequency characteristic implies that the electrical output will not give a true picture of the displacement. Although this frequency characteristic may be
. Electronic apparatus for biological research . Frequency Figure Response of electrodynamic transducer for constant input displacement Graph 9 shows that there is an essential difference between electrodynamic and piezo-electric transducers, although both give no output at zero frequency. Electrodynamic transducers can be constructed with very low mechanical impedance, suitable for use for measuring displacement. However, the rising frequency characteristic implies that the electrical output will not give a true picture of the displacement. Although this frequency characteristic may be linearized by passing the output through an integrating circuit (Chapter 3), it is usually possible to choose a more satisfactory type of transducer for the purpose. However, if information about the velocity of a system is required, the output of an electrodynamic transducer, suitably amplified, can be used to record this quantity directly. This avoids subsequent graphical differentiation of a displacement record and is the most useful application of this type of transducer. For qualitative work when, for example, only the frequency of a vibration or the time of occurrence of a transient mechanical disturbance is required, the simplicity and high sensitivity of certain types of electrodynamic trans- ducer are valuable. Thus, if an insect is attached to the armature of a moving- iron transducer ( a magnetic gramophone pick-up), the frequency of the output will correspond to the wing-beat frequency, even though the output waveform gives httle information about the forces to which the insect is subjected. Again, a piece of iron mounted on a rotating device will give several volts output in a nearby coil; this output may be used, for example, to synchronize a photographic flash with the rotation. Moving-iron transducers—In this type of transducer the coil is fixed, and a moving armature varies the reluctance of a magnetic circuit (Chapter 4) passing through it. The is
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