AC and meter movements
in [Basics]
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From: Mike Cook on 9 Apr 2010 04:48 How does one use AC to actuate a D'Arsonval (Weston) meter movement? Is a single rectifier sufficient? Bridge? Movement of interest says "FS = 45.8 uA DC". Extra points for links to drive circuits. Thanks.
From: Phil Allison on 9 Apr 2010 06:07 "Mike Cook" > How does one use AC to actuate a D'Arsonval (Weston) meter movement? Is a > single rectifier sufficient? Bridge? > > Movement of interest says "FS = 45.8 uA DC". > > Extra points for links to drive circuits. ** The simplest possible AC converter circuit use two germanium diodes, one wired across and one in series with the meter. This is what most anlogue multimeters use for the AC volts ranges. However, the sky is the limit if you go for active circuits using FETs, op-amps and even special AC to DC converter ICs that compute the "true rms" value of all manner of AC waveforms. ..... Phil
From: default on 9 Apr 2010 08:36 On Fri, 9 Apr 2010 01:48:28 -0700, Mike Cook <mcham(a)NOTyahoo.com> wrote: >How does one use AC to actuate a D'Arsonval (Weston) meter movement? Is a >single rectifier sufficient? Bridge? > >Movement of interest says "FS = 45.8 uA DC". > >Extra points for links to drive circuits. > >Thanks. If you have power to power the circuit something called a "precision rectifier" works well. It uses an op amp to effectively cancel the forward voltage drop of the diodes. If you haven't got power . . . and need sensitivity, the customary way is with a "copper oxide rectifier." These are old technology but still manufactured for this purpose, (but not in your local radio shack unless it is inside a meter you purchase there.) If you are just interested in making a meter for line voltages and starting out with a 50 micro amp movement, the drop of some forward biased germanium diodes is relatively insignificant. If you want to measure a few volts, germanium isn't going to work. Can one make a copper oxide rectifier? http://books.google.com/books?id=wN8DAAAAMBAJ&pg=PA582&lpg=PA582&dq=copper+oxide+meter+rectifiers&source=bl&ots=WK6TfGc8X-&sig=nfesu5FMzb19dv6Wcz2RYJ-ey7k&hl=en&ei=Txu_S5uaOYWClAf3htnnBg&sa=X&oi=book_result&ct=result&resnum=19&ved=0CFQQ6AEwEg how to make a Cu rectifier Popular Mechanics - Oct 1935 - Google Books Result Vol. 64, No. 4 - 256 pages - Magazine Dry-contact rectifiers are of various types; however, all of them include a common junction between two dissimilar substances. Some info on Cu rectifiers along with typical Fwd V drop: http://tera-3.ul.cs.cmu.edu/NASD/4dcb85c3-9fee-4c83-9e6d-fe6ce5522b59/China/disk4/75/75-3/31006598/PDF/00000134.pdf --
From: Phil Allison on 9 Apr 2010 08:44 "default" > > If you are just interested in making a meter for line voltages and > starting out with a 50 micro amp movement, the drop of some forward > biased germanium diodes is relatively insignificant. If you want to > measure a few volts, germanium isn't going to work. ** Huh ????????? Ge diodes begin conducting at less than 100mV. Only a matter of calibrating the scale on the lowest AC range to accommodate this. Millions of analogue multimeters made since the 1930s cannot be all wrong - eg: http://www.claytonengineering.com/Training/myweb6/MElect/FM%2055-509-1%20Chptr%209%20Circuit%20Measurement_files/fig9-28.gif ..... Phil
From: default on 9 Apr 2010 10:01
On Fri, 9 Apr 2010 22:44:15 +1000, "Phil Allison" <phil_a(a)tpg.com.au> wrote: > >"default" >> >> If you are just interested in making a meter for line voltages and >> starting out with a 50 micro amp movement, the drop of some forward >> biased germanium diodes is relatively insignificant. If you want to >> measure a few volts, germanium isn't going to work. > >** Huh ????????? > >Ge diodes begin conducting at less than 100mV. > >Only a matter of calibrating the scale on the lowest AC range to accommodate >this. > >Millions of analogue multimeters made since the 1930s cannot be all wrong - >eg: > >http://www.claytonengineering.com/Training/myweb6/MElect/FM%2055-509-1%20Chptr%209%20Circuit%20Measurement_files/fig9-28.gif > > > >.... Phil Curves of semiconductor diodes: http://www.tcc.edu/faculty/webpages/AKoon/cd/ETR%20104%20Labs%20and%20Handouts/Example%20Lab%20Report.pdf Probably loads cheaper to make meters with semiconductor diodes, but they still make copper oxide rectifiers for that purpose. Please put me back on your plunk list - you are an insufferable egomaniacal idiot Phyllis dear. -- |