Which probe to get?

[zachtheterrible]

I just bought this oscilloscope: **broken link removed**

It does not come with a probe, so i am wondering what kind of probe to get?

 

[David Bridgen]

You have, basically, two choices. A x1 or a x10 probe.

A x1 probe is effectively just a screened wire, so when you connect it to some point in a circuit you will be connecting the 'scope's input impedance (usually 1M) between that point and the circuit 0V (ground.)

A x10 probe presents an impedance of 10M to the circuit, at the expense of the signal to the 'scope being attenuated by a factor of 10 too.

What you buy will depend on your available funds of course, but a list of my preferences in ascending order of expense would be:

1. A x10 probe.

2. One each x1 and x10 probes.

3. Two x10 and one x1 probe.

4. Two of each.

 

[chemelec]

Alternately they make probes with a Switchable 1 or 10 factor.

 

[David Bridgen]

Of course, I forgot that Gary !

 

[Nigel Goodwin]

As David Bridgen said, a x1 probe is just a piece of screened wire, but it is fairly special wire, it's of very low capacitance (which is important).

A x10 probe includes a 9M resistor in series with the inner core, with a trimmer capacitor across it. The 9M resistor acts as a potential divider in conjunction with the 1M input impedance of the scope. The trimmer is adjusted to compensate for the input capacitance of the scope (including the probes cable) - whereas the resistor has to be 9x the input impedance, the capacitance has to be 1/9th of it's input capacitance.

Scopes commonly (always?) have a probe adjustment terminal on the front, you set the probe to x10 (if it's switchable) and clip it to the terminal. You 'should' get a nice squarewave on the scope, you adjust the trimmer capacitor until you do - it's VERY easy to do, and totally obvious where the correct point is.

Incidently, adjusting the capacitor is essentially a 'treble' control, just like on your HiFi - and gives exactly the same effect, which is why squarewaves are often used for testing amplifiers.

 

[David Bridgen]

The wire of the better x1 probes is also a bit resistive to attenuate reflections on the line.

 

[zachtheterrible]

So something like this would be sufficient: **broken link removed**

Thank you for all the information :lol:

 

[Nigel Goodwin]

So something like this would be sufficient: **broken link removed**

Yes, that's fine, scope probes are generally pretty standard things.

 

[Dean Huster]

I've spent 12 years in metrology (test & measurement), 6 of those with Tektronix, a total of 30 years in the hobby/industry. It is rare that a 1X probe will be useful for anything other than audio work.

The biggest problem with any probe, especially the 1X probe, is not the resistance presented to the circuit under test, but the capacitive reactance. In the case of the 1X probe, you can easily load down a circuit with just a couple of hundred ohms of Xc which will kill the signal, even with frequencies in the tens of kilohertz, let alone those that are higher. Any advantage in sensitivity you gain often is destroyed by the loading factor. So my advice is always for th 10X probe over the 1X if you have to decide upon just one.

The switchable probes are cute, but have lots of problems: (1) you often forget the switch setting and mess up an amplitude measurement; (2) switchable probes are always less reliable than single-factor probes; (3) the 1X setting of a switchable probe nearly always has significantly-less bandwidth capability than a single-factor 1X probe. The first problem is no problem if you have an probe with encoding and a scope with a probe-decoding ring around its BNC connector ... that usually limits you to a Tektronix scope. Even Tek's high-end P6063A switchable probe with 200MHz+ bandwidth in the 10X position had horrid bandwidth in the X1 position.

Dean

 

[zevon8]

Nothing wrong with that probe, have some very similar at work, TPI brand, etc.

there is one listed now on EBay:

**broken link removed**

Only issue I have ever had was the switch getting faulty. Mostly the probes were left on 10X anyways though. We got these probes for use in, shall we say, rough conditions where possible damage due to heat from hot components, etc during long testing cycles.

If you buy a used probe, say a TEK, make sure it comes with the proper (matching) cable and ALL the bits and pieces, like hook tip, etc.

 

[zachtheterrible]

The switchable probes are cute, but have lots of problems: (1) you often forget the switch setting and mess up an amplitude measurement; (2) switchable probes are always less reliable than single-factor probes; (3) the 1X setting of a switchable probe nearly always has significantly-less bandwidth capability than a single-factor 1X probe. The first problem is no problem if you have an probe with encoding and a scope with a probe-decoding ring around its BNC connector ... that usually limits you to a Tektronix scope. Even Tek's high-end P6063A switchable probe with 200MHz+ bandwidth in the 10X position had horrid bandwidth in the X1 position.

I dont plan on doing much RF work with this scope, its only 20MHZ, and there is not really anything that i would be doing down that low. Itll mainly be for audio work, possibly some digital if i get into that.
Its too late anyway, i already bid on it when i got to goahead from nigel :lol:

ah well, if it craps out on me, dropping another couple bucks wont kill me :lol:

 

[evandude]

I have these probes:

**broken link removed**

cheap, and they have a switch for x1/x10, and all the normal goodies, like a screw-on hook clip. I've been using them for months and they work just fine.

 

[Nigel Goodwin]

I've spent 12 years in metrology (test & measurement), 6 of those with Tektronix, a total of 30 years in the hobby/industry. It is rare that a 1X probe will be useful for anything other than audio work.

For service work a x1 probe is probably more often used than a x10, and I would recommend switched ones to be more versatile. I've been using switched probes for 35 years, and never seen a problem with them (except for the odd occasions they break down when being subjected to excessive voltage abuse!).

Probes generally are rated at 300-500V, I commonly use them on 1000V pulse - line output stage collector on TV's.