🚀 go-pugleaf

In article <1992Dec27.030536.1024@cmkrnl.com> jeh@cmkrnl.com writes:
>In article <BzwHA7.6y@zoo.toronto.edu>, henry@zoo.toronto.edu (Henry Spencer)
> writes:
>> In article <2B3582F9.18867@news.service.uci.edu> gkwan@balboa.eng.uci.edu
>> (Greg Kwan) writes:
>>>1. Get the best DMM you can--it's the most important test instrument.
>>>I have a Fluke 77 and have been very happy with it, but would probably
>>>go for an 87 or 79 now. You'll probably use the freq. counter since
>>>it's a pain to fire up the scope just to measure a frequency...
>> 
>> Note, though, that any frequency measurement using something other than
>> a scope relies heavily on assumptions about waveform.  When I first got
>> my current scope, I hoked up a little audio-frequency square-wave generator
>> with a 555 as an independent test signal.  I was a bit surprised to find
>> that my frequency counter read twice what the scope showed me.  
>> [...] There is no substitute for seeing exactly what's happening.
>
>I'll second this, and LOUDLY, too.  

I guess I was remembering my Hitachi V-1150 w/ its built-in frequency
counter and ``interpolated'' to the Fluke DMMs. Not quite the same, I
admit. I just hate counting hash marks or moving cursors (I'm REALLY
lazy :-). Definitely fire up the scope if there's any doubt.

>It appalls me to see frequency counters (and instruments like DMMs that include
>counters) that have no trigger level control, no input coupling selector (AC or
>DC), no edge selector (rising or falling).  You wouldn't buy a triggered-sweep
>scope without such controls; of what possible use is a counter without them? 

(I'm talking about scopes here.)
Even better, why not show the trigger level? If I'm remembering right,
the higher end Tek's (e.g. 2445, 2465, ...) show the trigger level, al-
though it's just a number (the voltage). The new Fluke 97 actually has
the trigger voltage superimposed (i.e. a line) on the signal. It doesn't
seem too difficult to add that feature and yet would help quite a bit.

One reason I don't use auto-setup buttons on scopes is that the scope
always has a different idea of what I want to see; they'll trigger on
the noise riding on a signal or something equally bizarre and leave
the volts and time scales at extremes.

>Anyone who trusts one of these counters without checking the waveform on a
>scope, if only to get in the right ballpark, is being as foolish as the person
>who thinks that a digital watch must be accurate simply because it isn't
>analog.  

I don't agree 100% here. I think counters are useful to get an idea of
what is going on in well behaved circuits. E.g. I'd use it to check AC
line frequency (60Hz [USA] is not fun to measure with analog scopes--
too much flicker) or to measure the frequency out of a signal generator
to make sure you're getting what you expect. Of course, I don't accept
as gospel every counter reading--just as I don't believe every volt
meter reading.

IMHO
greg

gkwan@balboa.eng.uci.edu