GB752520A - Power measuring instrument - Google Patents

Abstract

752,520. Power measurement. SPERRY CORPORATION. July 22, 1954, No. 21387/54. Class 37. In pulse-responsive peak power measuring apparatus, Fig. 1, a predetermined small percentage .of the pulse power supplied to matched load 14 through waveguide 12 from U.H.F. generator 11 (e.g. radar transmitter) feeds a temperature-variable resistor or barretter 19 having a time constant T (Fig. 2) which is long (e.g. 320 microseocnds) in comparison to the duration (e.g. 10 micro-seconds; #<SP>t</SP> in Fig. 2) of the pulses of power P p whose peak effective value is to be measured. A substantially constant current is maintained through barretter 19 via high-value resistors 21, 22 and voltageregulator tube 23 whilst the barretter 19 resistance increases from an initial value r1 to a higher value r2 throughout the duration of the applied pulses of power and the rate of rise or slope of the resistance change, r1 to r2, and accordingly also the slope of the voltage e, b across the barretter 19 varies directly as the peak value of the pulses of power and to obtain these peak values the voltage slope is measured and this may be done by taking e, b through amplifier 26 and differentiating in cathodefollower 29/31-34 to produce from cathode-load inductor 34 short pulses e, p shaped the same as Pp and whose peak varies as the peak of Pp and these voltage pulses e, p via amplifier 35 and cathode-follower 36 actuate peak pulse voltmeter 37 and oscilloscope 38 which exhibits e, p. If the instantaneous peak values of the power pulses Pp vary throughout the duration #<SP>t</SP> the barretter 19 effectively integrates these variations. The voltmeter 37 may read directly in milliwatts (for power pulses within the dynamic range of barretter 19) or the calibrated attenuator 16 feeding barretter 19 may be adjusted to a constant level (e.g. 100 milliwatts) corresponding to a fixed reference deflection on voltmeter 37. The variable attenuator 16 cooperates with a cross-guide coupler 13 which extracts a predetermined small percentage of the pulse power supplied to the matched load 14. The attenuation through attenuator 16 is read from its calibrated dial 17 and added to the predetermined fixed attenuation through coupler 13 to obtain the total attenuation between pulse generator 11 and barretter 19. Calibration check circuit, Fig. 1.-This circuit produces an output voltage similar to waveform E of Fig. 2 having a slope the same as the barretter output e, b for 100 milliwatts and'the operator applies this simulation voltage with switch S1 changed to a position and checks that pulse voltmeter 37 deflects to the 100 milliwatt reference mark. In the calibration circuit short positive pulses from blocking oscillator 41 and clipped to constant peak value by diode 56 and co-operating voltage regulator tube 59 feed long time constant integrating network 51 which delivers via a cathode follower 64 into a voltage divider 71, 72 which attenuates to the required (100 milliwatts).level. Modifications.-In Fig. 3 the barretter 19 is in series with an inductor 76 and constant voltage source 77 and the voltage drop across the inductor 76 and barretter 19 varies as the envelope of the power pulses. The barretter 19 feeds into a suitable amplifier 35<SP>1</SP> and the calibration check circuit of Fig. 1 is changed by deleting the integrating network 51 and re-adjusting the level of the short output pulses across resistor 72 to produce the 100 milliwatts reference deflection on voltmeter 37.