Buying and using an oscilloscope

[Bonky]

Thanks again Mark. I believe that the 'scope comes with a Hameg P6000 probe, so the croc clips lead would be of use (I think).

BW

Richard.

[ppppenguin]

When using a scope to probe circuitry it's usual to use a 10:1 probe. This reduces the capacitance which is loading the circuit. This often matters. You will gradually learn when it matters and when it doesn't.

This is analagous to the errors caused when using a voltmeter. Sometimes the resistive loading will matter, sometimes not. Usually matters more with analogue meters such as AVOs.

[Bonky]

Thanks again. The P600 probe is a 10:1 device I believe.

Cheers,

Richard.


  tek_p6000_old.pdf (Size: 334.35 KB / Downloads: 1)

[Terry]

Any advice as to whether I should buy more probes for the Hameg?

As it is a twin channel 'scope, you should have one 10:1 probe for each channel. These are important as they reduce the resistive loading on the circuit you are measuring from (typically) 1MΩ to 10MΩ but, more importantly in most cases, the capacitive loading is also reduced from (typically) ~30pF to ~3pF which greatly  reduces detuning effects.

Some important points to remember when using 10:1 probes:

- you must check the calibration before use. Connect the probe to the scope's internal calibration signal and adjust the controls for a reasonably sized display, then adjust the trimmer in the probe for the best waveform without rounded corners or overshoots.

- the chances of both scope/input combinations being identical is unlikely, so mark the probes to ensure that they are always connected to the same input.

- check the calibration from time to time and readjust as necessary.

- remember that the Y channel markings will now be wrong by a factor of ten so that a setting of, say, 100mV/division will equate to 1V/division due to the attenuation factor of the probe.

[ppppenguin]

While the capacititive loading at the scope's input socket is often around 30pF by the time you've connected a cable then there's often 100pF or so. Enough to seriously affect many circuits. Hence the use of a 10:1 probe. This reduces the capacitance in the same ratio as the attenuation. So in a practical probe, with the scope's capacitance plus that of the cable you'll typically end up with 10pF or so at the probe tip.

[Bonky]

Thanks very much; understood!

BW

Richard

[Craig]

Tektronix for decades have produced a probe primer called ABC's of Probes. As the years have gone by they have become increasingly useless. However, in my opinion the 1990 edition is the most helpful.

http://w140.com/tek_ABCs_of_Probes_1990.pdf

[ppppenguin]

That's a very good guide to probes and probing. Goes way beyond what Bonky and many of us need but it does no harm to understand the limitations of probes under difficult conditions.

[Bonky]

Thanks; just downloaded..and yes... it looks complicated!

R

[pwdrive]

Here you go boss:

https://www.youtube.com/watch?v=SX4HGNWBe5M

The guy does lots of good videos.

Lawrence.