Electrostatic Interference

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theo2 Active Contributor Join Date: Feb 2012 Posts: 13	Electrostatic Interference 02/10/2012 5:45 PM
	Here is another question i have studied long and hard and think i have the correct answer for it,,,,, Electrostatic interference can be nullified by, A: connecting the thermocouple ground to the positive side of the junction. B: twisting and grounding the thermocouple wires. C: shielding and grounding the signal leads. I believe the correct answer is C ,,, any comments?
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tonykuphaldt Power-User Join Date: Sep 2011 Location: Bellingham, WA Posts: 191 Good Answers: 46	#1 Re: Electrostatic Interference 02/10/2012 7:15 PM
	To be honest, all three answers look wrong to me. The only thing you should ground to guard against interference is the shield conductor of the cable (never the signal wires, which are the same as the thermocouple wires for a thermocouple circuit), and only at one end of the cable at that. For more information on how and why, check out the section in this book called "Electric Field (capacitive) De-Coupling": http://www.openbookproject.net/books/socratic/sinst/book/liii.pdf __________________ They call me "lightning" when wielding a hammer, because I never strike twice in the same place
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theo2 Active Contributor Join Date: Feb 2012 Posts: 13	#2 Re: Electrostatic Interference 02/10/2012 7:29 PM
	Thanks again for the reply! I think answer " C " ( Shielding and grounding the signal leads ) means make sure your wire is shielded and grounded, not actually grounding the signal leads,, Would that make it right?
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tonykuphaldt Power-User Join Date: Sep 2011 Location: Bellingham, WA Posts: 191 Good Answers: 46	#4 In reply to #2 Re: Electrostatic Interference 02/10/2012 8:24 PM
	Connecting the cable's shield wire to ground (at one end only) is the correct way to guard against electrostatic interference. I double-checked the link, and it works fine for me. It links you to a large PDF file (48 MB, so give it time to load! __________________ They call me "lightning" when wielding a hammer, because I never strike twice in the same place
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theo2 Active Contributor Join Date: Feb 2012 Posts: 13	#3 Re: Electrostatic Interference 02/10/2012 7:47 PM
	I cannot get the link to work for me
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dkwarner Guru Join Date: May 2006 Location: Placerville, CA (38° 45N, 120° 47'W) Posts: 6215 Good Answers: 248	#7 In reply to #3 Re: Electrostatic Interference 02/12/2012 12:29 PM
	It worked for me; about 2.5 minutes at around 300kB/sec. You may have to look wherever your download files go... __________________ Teaching is a great experience, but there is no better teacher than experience.
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rcapper Guru Join Date: Dec 2005 Location: Etats Unis Posts: 1871 Good Answers: 45	#5 Re: Electrostatic Interference 02/12/2012 2:23 AM
	It's C. B is for AC electromagnetic interference and A is just a bad idea. Although not commonly discussed, a high DC fields can cause errors due to hall effect. Then you need magnetic shielding, assuming you can't solve the problem the best way by avoiding proximity. __________________ The hardest thing to overcome, is not knowing that you don't know.
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Wal Guru Join Date: Jun 2011 Location: Phnom Penh Posts: 4019 Good Answers: 102	#6 Re: Electrostatic Interference 02/12/2012 7:29 AM
	This is starting to sound like the instrumentation School of the Air The question stated electroSTATIC interference. ie stray voltage. B; is obviously wrong as it renders the thermocouple inoperative. Its voltage will always be zero. C; is good installation practice to eliminate electromagnetic interference (EMI) A; provides a discharge path for any static charge and eliminates induced step voltages HOWEVER you want to be darned sure that the thermocouple will work in an unbalanced configuration and that there are no differential grounding potentials. Ask your tutor if the question really meant electromagnetic and not electrostatic. Are the terms interchangeable or I am just being an ornery cuss? What does your text book say? __________________ Difficulty is not an obstacle it is merely an attribute.
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theo2 Active Contributor Join Date: Feb 2012 Posts: 13	#8 Re: Electrostatic Interference 02/14/2012 7:55 PM
	This answer was also " C " ,,,,, I want to Thank You all again for all your input and advice on this question,,Thank You All !!
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dkwarner (1); rcapper (1); theo2 (3); tonykuphaldt (2); Wal (1)

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