REFERENCES 



Since the rate = I IT, it follows that provided t <^ T 



e =^ E X t X rate 



The system is open to two objections. One is the requirement that t be 

 much smaller than T, which means the arrangement becomes non-linear 

 at high count rates. The other is that when the input rate changes, e responds 

 only with a time constant RC, and if any attempt is made to shorten the 

 response time by reducing RC, the output voltage then fluctuates seriously 

 in step with each operation of the flip-flop. Much can be done to remove 

 these fluctuations by subsequent filtering but slow response remains as a 

 criticism and is in fact fundamental to this simple rate-measuring scheme. 

 Nevertheless, in this or in more elaborate forms, it is often used, e.g. by 

 Boyd and Eadie^"* in a heart-rate meter and in the author's frequency- 

 modulation tape recorder^^, where such a circuit is employed to measure 

 the frequency of flux-reversal in the magnetic tape. 



In an effort to produce a circuit which responds instantly to a rate change, 

 Andrew and Roberts^^ and Manzotti^'' have devised apparatus which 

 computes the reciprocal of the interval between the «th event and the 

 « + 1th, presenting the answer immediately upon arrival of the latter. This is 

 of course as quick-acting as is possible. The former authors' apparatus is for 

 displaying the rate of discharge of action potentials ; Manzotti's is a cardio- 

 tachometer. The way in which the requisite calculation is done in these devices 

 makes interesting reading, and it is not proposed to discuss them here. The 

 writer would, however, beg any reader contemplating quick-acting tachometry 

 to consider carefully whether the technique is really necessary, since the 

 apparatus required is liable to be complex. The cardiotachometer mentioned 

 employs 1 1 valves, most of which are double, and the nerve discharge-rate 

 meter contains 27. 



REFERENCES 



1 Attew, J. E. Wireless World 58 (1952) 1 14 



^ Dickinson, C. J. Electrophysiological Technique, Electronic Engineering 



3 Moody, N. F. and Williams, F. C. J. Instn. elect. Engrs. Pt. IIIA, 93 (1946) 



1188 

 * Kay, R. H. Electron. Engng. 28 (1956) 452 

 5 Bernstein, L. and Betts, J. C. /. Physiol. 110 (1949) IP 

 « CANfPBELL, F. W, and Gilmour, W. G. /. Physiol. 1 1 1 (1950) 2P 

 ' Hilton, S. M. and Lywood, D. W. /. Physiol. 123 (1954) 64P 

 ^ RoTBLAT, J., Sayle, E. A. and Thomas, D. G. A. /. sci. Instrum. 25 (1948) 33 

 » Gottlieb, I. Wireless World 60 (1954) 234 



10 Taub, D. M. Electron. Engng. 27 (1955) 386 



11 Kandiah, K. Electron. Engng. 26 (1954) 56 



12 Florida, C. D. and Williamson, R. Electron. Engng. 26 (1954) 186 

 " Kerkut, G. a. Electron. Engng. 27 (1955) 378 



1^ Boyd, W. E. and Eadie, W. R. Electron. Engng. 26 (1954) 330 



15 Donaldson, P. E. K. Electron. Engng. 27 (1955) 543 



i« Andrew, A. M. and Roberts, T. D. M. Electron. Engng. 26 (1954) 469 



" Manzotti, M. Electron. Engng. 28 (1956) 446 



655 



