MEASUREMENT OF PRESSURES 



199 



ray tube. The screen of the tube is photographed by a suitable camera, 

 a time scale being provided by motion of the film or by deflection of the 

 cathode ray tube trace. In either case, it is usually necessary to 

 brighten the cathode ray tube trace at the time of the event to be re- 

 corded, and if a linear time base is used its operation must also be syn- 

 chronized. Suitable triggering signals can be obtained by a gauge or 

 other device operated by the pressure wave, or from an electrical circuit 



GAUGE 



CABLE 



TRIGGER 



CALIBRATION 

 VOLTAGE 



MASTER 



CONTROL 



UNIT 



AMPLIFIER 



CAMERA 



TIME BASE 



CALIBRATION RRir,HTF-rjpR 



FREQUENCY ^ ^ BRIGHTENER 



TIME DELAY 



BLOCK DIAGRAM OF EQUIPMENT 

 FOR TRANSIENT RECORDING. 



Fig. 5.23 Block diagram of equipment for transient recording. 



firing the explosive charge ; in some cases it is convenient to include an 

 electrical delay circuit. Both the time resolution and voltage sensi- 

 tivity must be calibrated in terms of suitable standards. In order to 

 insure efficient and dependable operation of the entire equipment vari- 

 ous auxiliary items of equipment are desirable, such as partly or fully 

 automatic control circuits and regulated voltage supplies. The vari- 

 ous components of a complete recording system are described more fully 

 in what follows. 



A. Amplifier circuits. The specific requirements of signal ampli- 

 fiers for recording explosion transients depend, of course, both on the 

 transient and the gauge or transducer used. In any case, the amplifier 

 system must be stable and rugged, possess sufficient gain and frequency 

 response, and be capable of providing an adequate linear output signal 

 to the cathode ray tube. An amplifier used with piezoelectric or other 

 high impedance sources must also have a high input impedance in order 

 not to distort the input signal. 



