[sdiy] Multimeter and oscilloscope probes

Harry Bissell harrybissell at wowway.com
Fri Nov 5 14:13:15 CET 2010


oooh I know <raises hand>

DO NOT consider multimeter probes suitable for an oscilloscope. They are
not useful in the least.

You need (imho, hell... in my very NON-humble o) a minimum of a 10X probe for an oscilloscope.
It may seem counter-intuitive, but a 10X (divides the signal by 10) probe is essential for
quality work. A 1X probe usually has an impedance of 1 meghom, far too low to observe circuit operation without seriously loading (changing) the circuit.  

There are switchable 1X/10X probes. They are OK. I bought a set from ProbeMasters (iirc) that had
(1) 1X, (1) 10X, and (1) 1X/10X so you could have a pair of matched probes of either 1X or 10X. This is important for making differential, pseudo-differential measurements, or just to compare two circuit points with identical response.

BE SURE to choose scope probes that match your scope's frequency response and input capacitance !
(they could be 'faster" ie 100MHz probes would usually work on a 50MHz scope, but if the capacitance is quite different, performance will suffer greatly - you won't be able to trust what you see...)

Someone on the list poined out some Chinese made probes that were like $7. I forget the link but I bought a couple of sets and they seem OK to me.

Treat the probes like gold, don't bend, twist etc. And WATCH them carefully. Do you know how they got the name "10 to 1" probes ??? Turn your back on them for a moment and the "ten to one" away...

Meter probes are usually "DC" and don't affect measurements much. The 'mini-hook' and crocodile
leads you suggest sound just fine. For DIP packages they make adapter clips that look like spring clothespins. I'd try to get some old ones as they are just about obsolete and not used much anymore, they should be easy to find in any engineering departments junk drawer or garbage can at this point...

H^) harry




----- Original Message -----
From: cheater cheater <cheater00 at gmail.com>
To: synth-diy <synth-diy at dropmix.xs4all.nl>
Sent: Fri, 05 Nov 2010 08:36:11 -0400 (EDT)
Subject: [sdiy] Multimeter and oscilloscope probes

Hi guys,
I have got a problem with selecting the right tools and I thought I
would ask the huge collective experience here what the best course of
action is :-)

I want to get more probes for my multimeters (both analog/VU and
digital ones). I would also like to get an oscilloscope at some point,
however for the purpose of synths (no gigahertz frequencies here) I am
assuming I could use the same probes with an adapter. I would also
like to be able to probe around and use the probes to listen to the
signals inside synths, on my headphones. There are several questions I
have ran into:

1. what's the best place to buy those things? After moving down to
Munich I have got most of my multimeters and repair equipment in
Conrad (except for another soldering iron and simple '813 DMM which I
got during my year in Berlin). I have a digital and an analogue
multimeter from Voltcraft that I got there.

2. What sort of leads will I find useful to have? Here's what I
thought might be useful:
a. 2x normal probes (that I have already, so no need to buy)
b. 2x super-thin probes (that I find I need already in some places I
can't reach otherwise)
c. 2x crocodile probes aka dolphin probes (no idea why??), for example
for clamping down on stuff
d. some crocodile leads (I think I have some of those already somewhere..)
e. 2x those syringe-style hook shaped probes
f. screw-down leads (screw down terminals, for example for ground)

are there any leads missing that I might need?

In addition I would like to get a BNC->4mm Banana converter, the kind
that you use with oscilloscopes. I don't have an oscilloscope here in
Germany, however here's the reasoning: i need a way to use all above
probes and convert them to 1/4" plug to plug into my mixer/preamp. I
need to be able to switch those probes around (so they can't be
soldered shut). I can't DIY because I'm unable to find plugs that I
can diy that will work with test leads where the banana plug is
surrounded by a protective sheath. However, I have found a bnc to 4mm
converter that does all that: works with the protected test leads and
is made already and only costs 4 euro. I can then make a BNC->1/4"
converter and use it that way. I can also use that later if I want to
use a scope.

3. if I get an oscilloscope, will I have good results using the
multimeter probes? It's not for debugging ddr memory busses, or for
counting jitter on an xtal, it's mostly for synth repair and/or
design. Mostly analogue, some digital design too, can't hurt to be
able to do low-frequency digital (up to say xx MHz speed uC's). So I
take those probes I have listed above, plug them into the converter,
and off I go. The bonus here is: I can mix and match, so for example I
can clamp down the GND, whereas I use a hand held probe for the +
signal. What are the negative sides of using such a converter? What
should I watch out for? What should I watch out for when buying the
test leads? I am thinking that maybe there's some sort of test leads
that I can buy for my dmm that will also be very good for the
oscilloscope, whereas if I just pay 5% less I will get something
that's still good for the DMM but very bad for the oscilloscope - I
want to prevent this mistake, and would like to get something that's
good for oscilloscopes too. What is the actual difference between
multimeter and oscilloscope probes?

4. can I get a solderable BNC plug (female) somewhere? Or is it better
to use a ready lead and just rip off one end, replacing it with a
1/4"? Or even cut it in half and have two 1/4" converters..

5. Is there anything else missing in your opinion? I am mostly unsure
about what test probes I should be getting in order to test things
like DIP packages. For example some hook style probes seemed to big
for that and it seemed like they were only made for use with
through-hole elements. I'm also thinking about some some sort of test
lead that can go under a tightly soldered capacitor and access the
leads there (it would have to be a very thin plate of some sort?)
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-- 
Harry Bissell & Nora Abdullah 4eva



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