of the prototype were retained and several improvements 

 contributing to simplicity of operation were incorporated in 

 the new design. The calibration method has been simplified, 

 as has the bridge balancing -null detection operation.. The 

 new units are known as TMB Type 286-1A and are used with the 

 Sanborn driver amplifier 2 , power supply 3 , and recorder „ 



PART I 



DESIGN 



GENERAL 



The wave-height recording system consists of a gage, the 

 associated electronic system, and the recorder,. The gage is 

 essentially a capacitive transducer, the capacity varying 

 linearily with the water height „ This gage is used in a 

 capacitive bridge energized with a 10-kc carrier signal. 

 The signal recovered from this bridge is demodulated in a 

 phase-sensitive detector and further amplified . This 

 signal is then fed to* the Sanborn driver amplifier and to the 

 recording pens. 



GAGE 



The gage consists of a length of No. 28 enameled wire, 

 stretched taut, insulated from the water, and positioned 

 vertically through the water surface. The conductor forms 

 one plate of the capacitor, the water forms the other plate 

 of the capacitor, and the enamel is the dielectric. Since 

 the plate area formed by the water varies linearily with 

 the height of the water (if the thickness of the enamel 

 dielectric is uniform), the capacity of the gage is a linear 

 function of the water height. The gage gives a large AC of 

 about 50 uuf per inch of water. For a more complete 

 discussion of the gage, see TMB Report 859, "An Electronic 

 Wave-Height Measuring Apparatus o"" 1 



CARRIER SYSTEM 



Bridge drive is provided by a bootstrap oscillator and 

 driver of fairly conventional design. This drive is link 

 coupled into the bridge. Both the input and the output of 

 the bridge are resonated at the carrier frequency. Thus, a 

 high-drive voltage is obtained at a small outlay in power, 

 and the bridge output is multiplied by the resonant output 

 condition. Bridge output signal shifts 180 degrees in 

 phase with change in direction of bridge unbalance. 



