[Test-Equipment] Question regarding antique LCR bridge

[Barry]

Not quite.  Are you saying that I should be able to measure wirewounds more effectively with the bridge than other types of resistors?  I haven't tried a wirewound but will do that and see.  Carbon comps were common at that time so if it wasn't designed to work with those, wouldn't it have stated so in the manual?

Thanks,
Barry - N4BUQ


 On Tue 10/04/12  1:37 PM , rbethman at comcast.net sent:
> Barry,
> 
> As you noted, 'Designed in 1960'.
> 
> Therefore, it was built 'that' way to account for the wire-wound
> resistors of its time.  All of those, with the exception of
> non-inductive, i.e., Globar types, had both a capacitive *and*
> inductive component.
> 
> Now you are trying to measure today's components, whether carbon
> film, metal film, or others, even carbon composition types.
> Your bridge doesn't understand that those are what is currently used
> and purchased.
> 
> Make sense?
> 
> Bob - N0DGN
> -------------------------
> FROM: "Barry" 
> TO: test-equipment at mailman.qth.net [2]
> SENT: Tuesday, April 10, 2012 10:06:49 AM
> SUBJECT: [Test-Equipment] Question regarding antique LCR bridge
> 
> I have a Marconi TF1313 LCR bridge (designed in 1960).  When
> measuring L or C, the bridge is fed with an AC signal (1KHz or
> 10KHz).  The output goest to a couple of amplifiers and the detected
> signal is fed to a meter.  When the bridge approaches balance, the
> detected signal approaches zero and the meter indicates a null. 
> Standard stuff for a bridge.
> When measuring R, though, a DC (full-wave rectified, unfiltered)
> signal is fed to the bridge and the output is connected to the input
> of the first amplifier through a chopper (old fashioned vibrator). 
> Amplification and detection is the same process as for L and C.
> 
> My question is why it is necessery to change the configuration of the
> bridge for R measurement?  Why wouldn't it work with an AC input for R
> the same as for L and C and eliminate the chopper?  Wouldn't a
> balanced bridge made entirely of R produce a minimum signal at the
> output and allow for null detection?
> I know the answer is probably simple but I don't see why this is done
> this way.
> 
> Thanks,
> Barry - N4BUQ
> 
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