Electronic apparatus for biological research Electronic apparatus for biological research electronicappara00dona Year: 1958 ELECTROMECHANICAL TRANSDUCERS sometimes provided while other designs employ the damping effects of eddy currents induced in a metallic coil former. In all cases some additional mechanical resistance is introduced since the driving amplifier has a resistive output impedance. Figure Equivalent circuit of pen recorder The equivalent circuit of the mechanical parts of a pen recorder is shown in Figure Here R^ is the mechanical resistance induced by the output
Electronic apparatus for biological research Electronic apparatus for biological research electronicappara00dona Year: 1958 ELECTROMECHANICAL TRANSDUCERS sometimes provided while other designs employ the damping effects of eddy currents induced in a metallic coil former. In all cases some additional mechanical resistance is introduced since the driving amplifier has a resistive output impedance. Figure Equivalent circuit of pen recorder The equivalent circuit of the mechanical parts of a pen recorder is shown in Figure Here R^ is the mechanical resistance induced by the output resistance of the driving amplifier, R^ and R^ are the resistances (if any) due to oil and eddy current damping, m^ and m^ are the effective masses of the coil and pen, and Q and Cg are the compliances of the coil control spring and the pen coupling spring. The displacement of the pen is represented by the charge flowing through m^. By suitable choice of the components it can be arranged that the sensitivity of the recorder is constant from zero frequency to, in a typical case, 100 c/s. This adjustment depends, of course, on R^ having the correct value. It is usual in the design of driving amplifiers for pen recorders to provide a variable degree of negative feedback. The output impedance of the amplifier may thereby be varied {cf. Chapter 11), and hence the value of R^ may be controlled. If Ry is too small there will be a resonant peak in the response of the recorder and the response to a transient will be oscillatory. (a) > > > > > (b) (0 20 ^ 60 I 100 150 c/s Figure Frequency response and transient response of pen recorder: (a) under-damped; (b) correct damping; (c) slightly over-damped If R^ is too high the transient response will be over-damped. A technique for adjusting the damping is thus available; a low-frequency square wave is applied to the recorder, and the feedback control adjusted until it is reproduced most faithfully. In Figure the sq
Size: 2219px × 901px
Photo credit: © Bookworm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: archive, book, drawing, historical, history, illustration, image, page, picture, print, reference, vintage
