RECORDING OF METEOROLOGICAL SOUNDINGS 



105 



FRCQUENCY 

 CCNERATOR 



MCTCOROLOCICAL 

 CLEMENTS 



ELEMENT SWITCHING 

 AND 

 VOLTAGE CONTROL 



SERIES 

 H LIMITCR 



CATHOOe 

 FOLLOWER 



TWO- STORY 

 AMPLIFIER 



RECORDER 



Figure 4. Basic components of amplifier-recorder. 



the hygrometer or temperature elements. Any lock-in 

 device must be inherent in the equipment as remote 

 from the voltage appearing across tJie elements. This 

 principile has been incorporated in the design of the 

 equipment. 



Since the electrolytic hygrometer element can be 

 designed so that it will not polarize under direct cur- 

 rents approaching 100 /^a, it appears clesiral)le to design 

 the recording equipment for possible adaptation to 

 this type of element. In other words, the amplifiers 

 must be capable of handling direct currents as well as 

 alternating currents. 



Cable Eeeoe 



If the standard temperature and hygrometer curves 

 are used originally for calibrating the recorder, it is im- 

 23ortant to note that the cable resistance will introduce 

 a positive error. For average Southwest Pacific climate 

 and sounding heights up to about 3,000 ft, the positive 

 temperature error is roughly 1.5 F while the positive 

 hygrometric error is about 5 per cent EH. 



These errors, unfortunately, cannot be compensated 

 without complete i-ecorder calibration at the outset or 

 by mathematically adjusting the standard calibration 

 curves. Thus, since the cable is a fixed resistance, the 

 standard curve can be recomputed to allow for any 

 fixed cable resistance, with the result that no error 

 will be introduced into the recorder. 



In consideration of the above requirements, it will 

 be necessary, in adapting the standard U. S. Weather 

 Bureau electric hygrometer and temperature elements, 

 to provide (1) a means of developing a stable low- 

 frequency voltage across the elements, (2) to switch 

 from one element to another in measuring tlie voltages 

 across these elements, (3) to amplify such voltages, 

 (4) to provide a means of controlling the sensitivity 

 and range of the recorder, and ( 5 ) to supply the output 

 of the amplifier to a to 500 microammeter auto- 

 matic recorder. 



Electronic Amplifiers 



The basic components of the amplifier-recorder are 

 shown in Figure 4. The frequency generator operates 

 at 10 c and is composed of three units, (1) a phase- 

 shift oscillator, (2) a paraphase amplifier, and (3) a 

 controllable push-pull output amplifier. 



The amplifier-reeorder unit is composed of (1) a 

 series limiter, (2) a cathode follower, and (3) a two- 

 story amplifier, as shown in Figure 5. For the sake 

 of simplicity, the automatic switching device that 

 changes the current from hygrometer to temperature 

 element has been shown schematically. The switching 

 takes place at any rate between approximately 1.0 to 

 0.1 c ; this rate is not critical. 



Since the amplifier must be able to handle either 

 direct or alternating current, the balanced two-story 



r^iso 



TEMPtRATURE 

 ELEMENT 



-150 



Figure 5. Automatic recorder circuit. 



