as a continuous trace on a smoked glass slide, sea water temperature 

 versus depth. The depth element of the 180- and 450-foot models 

 consists of a spring-loaded piston enclosed in a flexible envelope 

 made of three brass bellows soldered together; in the 900-foot instru- 

 ment the spring is outside of the bellows assembly. The slide holder 

 is attached to one end of the bellows. As the instrument is lowered into 

 the sea, increasing water pressure tends to collapse the bellows and 

 compress the spring, thus moving the slide holder. The springs in the 

 three BT models are of such proportions that, with a pressure corre- 

 sponding to their respective depth ratings, the slide will move 0.7 inch. 

 If the depth limit is exceeded, the bellows and spring become distorted, 

 and the depth calibration of the BT is altered. Within its operating 

 range, the depth sensor of the BT is accurate to about one percent of 

 total depth. 



(3) Hollow spring 



The Bourdon tube is a hollow spring. In oceanographic 

 work the Bourdon tube usually is coupled to a variable resistor or to 

 a potentiometer circuit which is used as a transmitter. The North 

 Pacific Fisheries Exploration and Gear Research have developed such 

 a depth telemeter. The sensing element contains a Bourdon tube which 

 actuates a pressure potentiometer. Extensive use at sea in trawling 

 work seems to bear out the reliability and accuracy of this instrument. 



Karl Schleicher described a deep electronic bathythermograph in 

 1953. Pressure is measured by means of a helical Bourdon tube that 

 has a range of zero to 2,700 p.s.i. The Bourdon tube moves the core 

 of a Schaevitz transformer. The recorder is in the fish. Sensitivity, 

 the smallest reproducible change in the measured variable which will 

 cause a noticeable and measureable deflection of the recording pen on 

 the drum, is five p.s.i. (about ten feet). No data are given on the 

 accuracy of the instrument under field conditions. 



Also in 1953, S. J. Knott described a depth meter containing three 

 Bourdon tubes with ranges of 250, 500, and 1,000 feet. Laboratory 

 calibration gave an accuracy of ± 1 percent or less of full scale. 



In 1955, Boden, Kampa, Snodgrass, and Devereaux described a 

 depth telerecording unit which employs a Bourdon tube to actuate a 

 potentiometer. An accuracy to within ±0.5 percent of the actual depth 

 in the range of zero to 1,000 meters was stated. 



Willard Dow, also in 1955, described an acoustic telemetering 

 depth meter. The submerged device contained a stable heterodyne 



V-3 



