Reading a Machine tas summer 2006


Download 515 b.
Sana01.04.2018
Hajmi515 b.


Reading a Machine TAS Summer 2006 Carol Wenk Email: cwenk@westfieldnjk12.org


Bimetallic Switch: How does it work?

  • Metals expand when heated

  • A strip of 2 different metals that are connected (coil is more sensitive)

  • Metals will have different rates of expansion

  • If metal on inside of coil expands more when heated, coil will unwind



Thermostat: How does it work?

  • Temperature lever attached to center of bimetallic coil.

  • Mercury tilt switch attached to end of coil. When mercury contacts wires, a circuit is closed. (Need to mount level)



Mercury Use

  • Hg barometer: Toricelli 1643

  • Hg thermometer: Fahrenheit 1714

  • Hollerith tabulating machine & sorter 1890



Thermostat: How does it work?

  • Heat anticipator (resistor): Based on setting, current travels through resistor. Generates heat, which warms coil. Shuts off heat before room heat actually reaches thermostat.



Variations: Digital Thermostats

  • Thermistor: Electrical resistance changes with temperature. Converts resistance to temperature.

  • Programmable thermostats



Bimetallic Switch: History

  • Invented by English carpenter & clockmaker John Harrison in 18th century (1739-1749).

  • Developed precise marine clocks (chronometer) to calculate longitude. Bimetallic strip compensated for temperature changes in the balance spring.

  • When receiving Copley Gold Medal, referred to invention as Harrison’s “new metalline thermometer”.

  • Memorial in Westminster Abbey, England in 2006.



Harrison’s Temperature Compensation



Bimetallic Switch: Applications

  • Bimetallic strip thermometers: Johann Lambert & David Rittenhouse in 1767 in Philadelphia; James Crichton in 1803 in Scotland.

  • Meat & candy thermometers. Uses a helical bimetallic strip to turn needle, or uses gears like in a watch.



Bimetallic Switch: Applications

  • Toasters:

  • 1st electric (no controls): Frank Shailor of GE in 1909

  • Toastmaster pop-up by Charles Strite in 1919

  • Late 1920s use bimetallic strips

  • Sunbeam in 1940s improved bimetal (based on bread, not heating element)



Bimetallic Switch: Applications

  • Automatic Coffeepot: Russell Hobbs in 1952; bimetallic strip stops device when coffee is perked.

  • Waffle irons: Manning-Bowman Twin-O-Matic with thermostat & thermometer using bimetallic strips in 1939 by Alan M. Young.

  • Aneroid barometer (non-mercury): 1st idea by Leibniz in 1700; Lucien Vidie in 1843.

  • Hair dryer safety cut-off switch (1st dryers 1925; safety 1970s)

  • Circuit breakers: strip bends to open circuit; 1904



References

  • Howstuffworks.com/home-thermostat.htm

  • virginia.edu/supplements/thermometers_and_thermostats.pdf; John Wiley & Sons, Section 6.6 Thermometers & Thermostats, 2001.

  • En.wikipedia.org/wiki/bimetallic_strip; John_Harrison

  • William J.H. Andrewes, The Quest for Longitude (Cambridge, MA: Collection of Scientific Historical Instruments, Harvard University, 1996).

  • Dava Sobel & William J.H. Andrewes, The Illustrated Longitude (New York: Walker and Co., 1995).

  • www.madehow.com/Volume-7/Hair-Dryer.html; Aneroid-Barometer.html; Toaster.html

  • www.madehow.com/Volume-4/Mercury.html

  • www.bookrags.com/sciences/sciencehistory/thermostat-woi.html

  • Trove Reference & Education: Science in Scotland: findarticles.com/p/articles/mi_rlg4413/is_SLGG0003/ai_n15607125

  • www.greatachievements.org/?id=3768

  • 199.249.170.176/europastar/watch_tech/nicolet6.jsp

  • eo.ucar.edu/skymath/tmp2.html

  • www.americanheritage.com/articles/magazine/it/2005/2/2005_2_6.shtml

  • www.nmm.ac.uk/server/show/conWebDoc.355/setPaginate/No

  • www.ce.berkeley.edu/Courses/E77/lecturenotes/1intro.pdf

  • hyperphysics.phy-astr.gsu.edu/hbase/thermo/bimet.html

  • www.jitterbuzz.com/indirn.html; waftrip.html

  • www.madehow.com/Volume-6/Clothes-Iron.html

  • www.columbia.edu/acis/history/census-process.jpg

  • www.facstaff.bucknell.edu/mastascu/elessonshtml/Sensors/TempThermCpl.html

  • www4.tsl.uu.se/~Atlas/DCS/DCSIL/therm.html



Download 515 b.

Do'stlaringiz bilan baham:




Ma'lumotlar bazasi mualliflik huquqi bilan himoyalangan ©fayllar.org 2020
ma'muriyatiga murojaat qiling