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Bimetallic  Expansion  Thermometers
Resistance Temperature Detectors

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Figure  11-13.—Distant-reading,  Bourdon-tube  thermometer. There   are   two   basic   types   of   filled-system thermometers.  One  type  has  a  Bourdon  tube  that responds primarily to changes in the volume of the filling fluid. The other type has a Bourdon tube that responds primarily to changes in the pressure of the filling  fluid. A distant-reading thermometer (fig. 11-13) consists of a hollow metal sensing bulb at one end of a small-bore capillary tube. The tube is connected to a Bourdon tube or other device that responds to volume changes or pressure changes. The system is partially or completely filled  with  a  fluid  that  expands  when  heated  and contracts  when  cooled.  The  fluid  may  be  a  gas,  an organic liquid, or a combination of liquid and vapor. PYROMETERS Pyrometers  are  used  to  measure  temperature through a wide range, generally between 300°F and 3,000°F. Aboard ship, pyrometers are used to measure temperatures  in  heat  treatment  furnaces,  the  exhaust temperatures  of  diesel  engines,  and  other  similar purposes. The pyrometer consists of a thermocouple and a meter (fig. 11- 14). The thermocouple is made of two dissimilar metals joined together at one end. It produces an electric current when heat is applied at its joined end. The  meter,  calibrated  in  degrees,  indicates  the temperature at the thermocouple. ELECTRICAL   TEMPERATURE MEASURING  DEVICES On  newer  propulsion  plants,  you  will  monitor temperature  readings  at  remote  locations.  Expansion thermometers provide indications at the machinery locations  or  on  gauge  panels  in  the  immediate thermometer  area.  To  provide  remote  indications  at  a central  location,  electrical  measuring  devices  along  with signal  conditioners  are  used.  The  devices  discussed  in this section include the resistance temperature detectors (RTDs),  resistance  temperature  elements  (RTEs),  and Figure  11-14.—Diagram  arrangement  of  a  thermocouple. 11-7






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