. Bathythermograph observations. Bathythermograph; Ocean temperature. angles to the direction in which the stylus moves to record temperature. When the BT is raised toward the surface, the spring expands the sylphon to its original shape. Thus the trace scratched on the smoked surface of the slide is a combined record of temperature and pressure, the pressure being propor- tional to depth. Since external pressure slightly affects the internal pressure of the xylene in the bourdon, and since temperature changes also influence the movement of the sylphon, each instrument must be carefully calibr
. Bathythermograph observations. Bathythermograph; Ocean temperature. angles to the direction in which the stylus moves to record temperature. When the BT is raised toward the surface, the spring expands the sylphon to its original shape. Thus the trace scratched on the smoked surface of the slide is a combined record of temperature and pressure, the pressure being propor- tional to depth. Since external pressure slightly affects the internal pressure of the xylene in the bourdon, and since temperature changes also influence the movement of the sylphon, each instrument must be carefully calibrated by the manufacturer. A special grid is supplied for each instrument for converting the stylus trace to temperature and depth readings. From an examination of the grid, yoo will note that the temperature lines are not exactly straight and vertical, but curve slightly to the left with increasing depth. Likewise, the depth lines are â not exactly arcs of circles with radius equal to the length of the stylus, but also allow for thermal ex- pansion of the sylphon. At a temperature of 105° F, the recording stylus brings up against a stop pin; if this temperature is exceeded, permanent deformation of the brass coil of the bourdon will occur, and the calibration of the instrument will be ruined. For this reason, the BT must always be kept out of the sun and away from the vicinity of fire rooms, steam pipes, and so forth. An instrument that has been overheated may often have the stylus arm jammed by the pen-lifter bar in the high-temperature position. If another BT is aboard, use it and turn in the damaged instrument for adjustment. If a spare is not available, gently lift the stylus arm from the pen-lifter bar and let the arm swing back toward the low-temperature side. The temperature calibration will henceforth be in error as a result of deformation of the bourdon. Record on the BT log sheet that the BT calibration is uncertain beginning with the next slide, and turn in the i
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Keywords: ., bookauthorunitedstateshydrographicoffice, bookc, bookcentury1900
