DYNAMIC MEASUREMENTS ON ELECTROMAGNETIC DLVlCLb 1 107 



Thus we have shown the new expression more accurately represents the 

 eddy current effect on the initial flux rise for speed coils, and for most 

 relays the overall accuracy will be within 2 per cent, and all relays should 

 be within 4 per cent, an error reduction of about two-f birds compared to 

 the older approximation. 



EQUIPMENT 



The dynamic fluxmeter is sho^v^l in Fig. 26. Two panels, each with a 

 subchassis attached, comprise the set. The dc instrument and a supple- 

 mentary voltmeter and ammeter are on the bench beside the cabinet. 

 The upper panel contains the timing system, with the time selection con- 

 trols. The lower panel includes the power supply and the test relay circuit 

 controls, including the mercury contact relays. The control keys arrange 

 the test relay circuit for any test condition. 



The optical probe, a test relay, and the dc amplifier system are shown 

 from left to right in Fig. 27. The photocell is in the shielded container 

 above the relay, with the lamp and lens system below. A right angle 

 prism turns the light beam into the vertical, to pass between the vanes 

 on the relay. 



The upper panel of the bench rack is the —250- volt supply. The lower 

 panel includes the +250-volt supply, the three dc amplifiers and the 

 magnetically shielded air-core output transformer. Its secondary is con- 

 nected to the fluxmeter through a shielded cable. The controls are for 

 zero setting the dc amplifiers, for selecting the amplifier gain and whether 

 a displacement or velocity measurement is to be made. 



REFERENCES 



1 E L Norton, Dynamic Measurements on Electromagnetic Devices, A.I.E.E. 



Trans.,64, p. 151, April, 1945. „ . ,. ^. . ^„ .. 



2. Keister, Ritchie and Washburn, The Design of Switching Circuits, D. Van Noe- 



strand, 1951. ^ ^, „. ,^«« 



3 Otto Schmidt, Thermionic Trigger, J. Scientific Instr., 16, p. 24, 1938. 



4. Richard Weissman, Stable Ten-Light Decade Scaler, Electronics, 22, May, 



1949. 



5. M. Artzt, Survey of DC Amplifiers, Electronics, Aug. 1945. 



6. Bode, Network Analysis and Feedback Amplifier Design, I). \ an Xostrand 



7. R. M.Bozorth, Ferromagnetism, D. Van Nostrand, 1951, Chapter 17. 



