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From: zben@umd5.UUCP
Newsgroups: net.analog
Subject: Re: AC current monitor
Message-ID: <447@umd5.UUCP>
Date: Sun, 24-Mar-85 17:49:50 EST
Article-I.D.: umd5.447
Posted: Sun Mar 24 17:49:50 1985
Date-Received: Thu, 28-Mar-85 00:07:11 EST
References: <5139@fortune.UUCP> <445@umd5.UUCP> <446@umd5.UUCP>
Reply-To: zben@umd5.UUCP (Ben Cranston)
Distribution: net
Organization: U of Md, CSC, College Park, Md
Lines: 28
Summary: Synthesis of two previous ideas 

-----+--------/\/\/\/\/\/\/\/\---------+--------
Line |             R1                  |    Load
     |                                 |
     +--\/\/\/\/\/-----()()()()()()----+
           R2          ============  Isolation transformer
                       ()()()()()()
                       |          |  -------       R3           |\
                       |          +--| ~ + |--+--/\/\/\/\--+----| >-- TTL out
                       |             |     |  |            |    |/
                       |             |     | --- +       \---\  Schmitt trigger
                       |             |     | --- C1    Z1 / \   Gate (74??)
                       |             |     |  |           ---       
                       |             |     |  |            |
                       +-------------| ~ - |--+------------+ 
                                     -------
                                     Full wave
                                      Bridge

This circuit has the advantage that the impedance to the load can never be
greater than the value of R1.  R2 limits the fraction of the load current
that goes thru the isolation transformer.  The bridge rectifies and C1
filters the 60 cycle.  R3 limits the current thru the zener diode Z1.  The
zener diode Z1 (~4v) ensures that the input to the gate can never get
higher than the +5 supply rail.

Gosh, I wonder if it would really work.... :-)
-- 
Ben Cranston  ...{seismo!umcp-cs,ihnp4!rlgvax}!cvl!umd5!zben  zben@umd2.ARPA