Chapter 25. -NEW DEVELOPMENTS IN NAVAL ENGINEERING 



27.351 



Figure 25-19. — Bridge Console. 



An additional level switch is employed in 

 bilges and unvented tanks. This switch is similar 

 in operation to that described in chapter 3 as a 

 float switch. 



Temperature Sensors 



Temperature is measured by means of re- 

 sistance temperature detectors (RTD).TheRTD 

 (fig. 25-21) consistsof a sensing element incased 

 in a protective tube. Since the electrical resist- 

 ance of the element changes with temperature 

 changes, the temperature can be determined by 

 measuring the resistance. 



For temperatures having a maximum of 600 

 degrees F., a nickel resistance element is used. 

 These detectors are found to be of the stem- sen- 

 sitive type, where the sensing element is located 

 within a few inches of the stem, or the tip- sensi- 

 tive type, where the sensing element is within the 

 tip of the detector tube which must be pressed 

 against the material being measured. 



Above 600 degrees a platinum element is em- 

 ployed in the stem- sensitive element type. Cur- 

 rently this is the only application of this type ele- 

 ment. 



In most applications the RTD is installed in 

 thermo wells, bored and threaded to receive the 

 detector. By the use of this method the unit may 

 be removed from the measured component or 

 piping without disturbing the integrity of the com- 

 ponent. Extra protection is also afforded to the 

 element in this manner. 



DATA SCANNER SYSTEM 



Figure 25-22 is a block diagram of the Data 

 Scanner system. The inputs from the sensing de- 

 vices are placed into the scanner (block 27) as 

 analog values. The scanner is an electronic se- 

 lector governed by the Synchronous Timing Gen- 

 erator (22), the Program Contact (23) and the 

 Point Drive (26). When there are no requests for 

 the system such as the Bell Log, Alarm Log, 

 Status Log, or Display Triggers, the scanner 

 continues to check each of the inputs. K there is 

 a request present, the scanner will go directly to 

 the address requested and process that signal 

 before monitoring all of the addresses. The 

 signals are sent to the Isolation Amplifier (28) 

 from the scanner, and after amplification it pass- 

 es on to the Analog/Digital converter (29). The 



647 



