Re: Opinions on Oscilloscopes

mike <spamme0@xxxxxxxxxxxx> wrote in news:433C606B.6030302@xxxxxxxxxxxx:

> RR wrote:
>> Hi,
>>
>> I'm in the process of teaching myself analog electronics. I figure
>> that my understanding of components and circuits will be enhanced by
>> being able to measure and view behaviour on a CRO.
>>
>> Initially I'll be building low voltage circuits (9V, 12V) in both AC
>> and DC. But I would like to be able to measure mains (I think I just
>> a differential probe with any scope for this) later on.
>>
>> My local ebay has two CROs that seem interesting and good value to
>> me: - a McVan BWD826
>> - a Tektronix 475
>>
>> I've read elsewhere on sci.electronics good opinions about BWD824 and
>> Tek 465b.
>>
>> Opinions on the above?
>>
>> Also, my other option is to buy a real cheap new 10MHz unit from a
>> local electronics store. A problem I see with it is that its minimum
>> sensitiviy is 5mV (I notice that usually it's 1mV or less). But, I
>> guess 5mV is probably small enough for my needs.
>>
>> It's also single channel. For what I want to do, am I going to need
>> 2 channels?
>>
>> Opinions please?
>>
>> Last question: if a scope says "Trigger Max. Input Voltage: 400V
>> peak", does that mean it will handle 240VAC input (I think 240VAC RMS
>> is 400VDC)? Would it still need a differential probe for this


Scope input is rated *DC plus peak AC*.
At least that is how Tektronix specs their scopes.
Why are you going to put 250VAC into the TRIGGER input? The scope usually
has an internal trigger pickoff AFTER the attenuator,to keep trigger
signals small but useable. External trigger is used when you have a clean
reference signal to use,like H or V drive from a video generator when
looking at composite video,eliminates the need for a sync spearator..

>> purpose?
>>
>> tia,
>> RR
>>
>>
>
> It's my opinion that if you need two channels, you're not gonna be
> happy with a single channel scope.
>
> The key to buying a scope is patience.
> You can't hardly go wrong with a TEK 400 or 7000 series scope.

7313,7500 series scopes SUCK big time.and TEK-made ICs are only available
thru cannabalizing other scopes,they are out-of-production and/or stock.

> Prices run from "way too much" to "dirt cheap" depending on where/when
> you buy one. Patience...
> You can find good deals on EBAY, but you have to know the right
> questions to ask and hope the answers are honest. Anything that says,
> "can't test it" is suspect.
>
> Search out a ham radio operator. Go visit a ham club meeting.
> Those guys have spare scopes for their spare scopes in the attic.
> Ham radio swap meets are a great place to buy scopes.
>
> Take someone with you who knows how to test a scope. It's not unusual
> to find a scope can put up a green worm, but has significant problems
> when it comes to actual use. Scopes are relatively easy to fix, until
> you get to a bad part that you can't get any more. Problem is that
> you usually need a scope to fix a scope.
>
> There's no reason to EVER put 240VAC into a scope. You'll always be
> using at least a 10X probe. Worry about the probe specs, especially
> on cheap probes.
>
> I'm gonna repeat myself. Scope probes are designed to be insulating
> and safe to use. Hanging random wires on 240VAC and stuffing that
> into a scope is a recipe for DEATH. Maybe not today, but eventually.
> Just don't do it.
>
> mike
>

The worst part about inputting line voltages is the grounding;in
switchers,what you think is ground may only be "common",and potentially hot
referenced to earth ground.

--
Jim Yanik
jyanik
at
kua.net
.

Relevant Pages

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  • Re: Opinions on Oscilloscopes
    ... But I would like to be able to measure mains (I think I just a differential probe with any scope for this) later on. ... It's also single channel. ... The scope usually has an internal trigger pickoff AFTER the attenuator,to keep trigger signals small but useable. ...
    (sci.electronics.equipment)
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