Using a scope

[Tom Cloud]

Fred .... this reminds me of the good ole boys line "I'm just
an old country boy" .... thir voices always go up about 1/8
note in pitch and I immediately grab for my wallet (to be sure
it's still there) ..... so, you don't really expect me to
fall for this "I'm just a poor ole boy what don't know
nothin" line, do ya  ??    8^)

At 09:29 AM 6/24/97 -0400, Frederic Breitwieser wrote:
>My scope has two seperate leads, one with an alligator clip, one with a 
>sharp point (mine's kinda flattened out actually), and putting across 
>anything automotive so far hasn't resulted in anything exploding, smoking, 
>or making sizzling sounds.  I do have a 100ma fuse in series with the 
>ground lead, which has popped on occasion.  Maybe my scope's input not be 
>grounded?  Or maybe its high impedence?  Maybe its just broken?  Its 
>certainly an old scope....

unless you've got an old Dumont or such that has a "Sync" instead
of a trigger (i.e. all vacuum tubes .... and still old even for
those days), the scope ground lead is connected to the AC line
ground -- check it with your ohmmeter.  There's normally
no problem since bench power supplies (and your car) are
isolated from the AC mains (unless the bench supply has
one of the outputs grounded or some other piece of equipment
hooked into the circuit is connected to the AC ground).

The 100 mA fuse should *never* blow -- after all, the
scope's input Z = 1 megohm (not counting the shield/ground
being connected to the chassis).

>>At 11:42 AM 6/23/97 -0400, Frederic Breitwieser wrote:
>>
>>>Fear not Mr. Mechanical <smile>, most 'scopes have a high enough impedance 
>>>(loading capacity) that you can snoop around circuits without causing
>>>issues, and you can directly attach your 'scope to the injector, and view
>>>the pulses directly.
>>
>>Fred .... remember that the scope probe ground clip is attached
>>directly to the scope chassis and then to the AC ground.  Care
>>needs to be taken where it's attached in a circuit -- it's
>>NOT high Z


Tom Cloud <cloud at peaches.ph.utexas.edu>