Figure C-ll. Recorder. Sippican model MK-2A. 



tor, two spools of wire, and the probe launch 

 pin. 



C-11 How the XBT Works.— The thermal 

 element of the XBT is the probe. It is a ballis- 

 tically shaped device containing a calibrated 

 thermistor in its nose. The thermistor is con- 



BREECH CONTACTS 



PROBE 



Figvrr C-lt<. Expendable probe and canister, Sippican 

 model T— 1 (cutaway view at left). 



XBT PROBE IS LAUNCHED 

 WITH SHIP UNDERWAY 



WIRE ON PROBE SPOOL 

 UNWINDS AS PROBE 

 SINKS 



WIRE ON CANISTER SPOOL 

 UNWINDS AS SHIP MOVES 

 AHEAD 



Figure C-19. Launching the XBT. 



nected to a very fine two-conductor wire.^ Ap- 

 proximately half of this wire is wound on a 

 si)ool inside the probe, and the other half is 

 wound on a spool inside the upper portion of the 

 canister. The probe is held in place in the canis- 

 ter by the probe launch i^in. To take an XBT, 

 the canister case is placed in the breech of the 

 launcher and the breech is locked, completing 

 the electrical circuit from thermistor to re- 

 corder; then the probe launch pin is jJuUed, and 

 the probe falls through the discharge tube and 

 into the water (fig. C-19A). When the probe 

 is launched, the fine wire from both spools is 

 free to unwind, permittmg the probe to free-fall 

 through the water and the ship to move away 

 from the station without breaking the wire (fig. 

 C-19B) . As the probe drops through the water, 

 the resistance of the thermistor in the probe 

 changes with the water temperature. This causes 

 voltage changes at the recorder, and the temper- 

 ature and depth- are recorded on an analog 

 chart. When all the wire on the spools is jsayed 

 out, the wire breaks, and the probe drops to the 

 bottom of the sea. 



C-12 Installation of XBT Launcher and 

 Recorder. — The XBT launcher and recorder 

 shown in figures C-16 and C-17 should be in- 

 stalled on the ship in accordance with manual 

 K-667A "Instructions for Installation, Opera- 

 tion, and Maintenance of Sippican Expendable 

 Bathythermograph System." In locating the 

 components on the ship, consideration should be 

 given to protection of the recorder from weather 

 and spray, to line voltages, ambient tempera- 

 tures, and electrical noise, to garbage chute and 

 waste outlet locations, and to the location of any 

 devices being towed by the ship. XBT probes 

 should be stored in a cool place out of direct 

 sunlight. 



C-10 



1 Various models of the XBT probe contain different lengths 

 of wire depending on the depth to be observed and the speed 

 of the launching ship. 



- The chart paper drive speed is constant and Is directly 

 proportional to the probe's assumed rate of descent. 



Change 1—1970 



