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oscilloscope 10x probe, good for me?

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patroclus

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I reciently purchased an old 20MHz analog scope, and I have no probes.
I will mainly use it in 5V circuits, to measure signals in the range of 0V-5V, sometime up to 12V, and very few, up to 15 or 20V.
I have the chance of getting at good prize, but not for free, 10X probes, but no 1X probes.

10X probes may atenuate the signal too much, so If I need to measure a 5V signal, 5V will be 0.5V, and so, these probes may be not suitable for me.

I looked up the sensibility of my scope, and it says 0.5 div internal, and 0.5V external... I'm not sure about what it means. what is minimun voltage change that can be measured? By the way vertical divisions ranges from 5mV to 5V.

Can you please give me some advice??

thank you!
 
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It's the vertical divisions you need to look at, so your 5mV per division will become 50mV per division.

I would STRONGLY suggest you buy switched x1/x10 probes - they are much more versatile.
 
When I bought my oscilloscope, I bought a pair of 1X/10X switched probes on ebay - they are clearly no-brand probes, but I am perfectly happy with their quality - and I paid something like $15 apiece for them, which is way less than "name-brand" probes are. You can find them for similar prices from places like web-tronics.com if you don't like ebay.
 
The most important benefit of 10x probes is that they present a much lower capacitance to the circuit being probed, and in most cases a higher resistance as well. But it is the lower capacitance that is important. With x1 probes you are placing the entire capacitance of the probe cable as well as the input capacitance of the scope itself across the point being measured. You just can't get good bandwidth with a x1 probe for this reason also.

It is routine to use 10x probes in every scope I've ever used and I can't imagine a scope that can't tolerate use of these probes. You just divide the vertical gain dialled up on the scope by 10, that's all. You can do this in your head, or with some scopes the probe has a special pin that tells the scope to change its vertical scale.
 
patroclus said:
but, could I use 10x probes well for a while? why are they usefull?

Yes they are, just not as useful as switchable probes - as long as they are very cheap, go for it!.

Like Radioron says, they give you 1/10 of the capacitance, and ten times the impedance (so 10Meg instead of 1Meg) - you need to adjust the trimmer on the probe to match your scope, which should (WILL!) have a squarewave output on the front for this purpose. If you don't do this, then you will get wrong readings, and wrong waveforms.
 
They are not very cheap, but they seem pretty good. Tektronik and HP probes, one of them with readout (which I don't know what it is).
They cost me like $25 each, but the tektronik one costs more than 100$ new (it is a 6109 Probe, 100MHz, 10X, 10Mo, 11.8pF)
The HP probe is a 500MHz probe, 10X, 6pF, 1Mo.

It may cost a lot... onlt $25 for me.
Both for 50$.

Should I go for them??
Or get 2 cheap new 1X non-brand probes for the same price??

I really do not need bandwidth now, as my scope is a 20MHz one...But considering the high prize these probes have in the new market, it seems like a good deal.
 
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patroclus said:
They are not very cheap, but they seem pretty good. Tektronik and HP probes, one of them with readout (which I don't know what it is).
They cost me like $25 each, but the tektronik one costs more than 100$ new (it is a 6109 Probe, 100MHz, 10X, 10Mo, 11.8pF)
The HP probe is a 500MHz probe, 10X, 6pF, 1Mo.

It may cost a lot... onlt $25 for me.
Both for 50$.

Should I go for them??
Or get 2 cheap new 1X non-brand probes for the same price??

No, don't buy x1 probes - spend a little more and get switched x1/x10 probes.

I've just checked in RS Components, a x1 probe is £15, a x10 is £17, and a x1/x10 is only £18 - it makes far more sense to have switched probes.
 
so, maybe go for the 1x/10x probes and forget about these tektronik and HP ones, even though they seem quite expensive ones??
 
It's possible that the input capacitance of the old 20MHz scope may be so high that the compensation cap on the good probes he is considering buying won't have enough range to properly compensate them. They would then be useless until he gets a better scope.
 
patroclus said:
my scope's input impedance is 25pF, and 1Mohm.
Do you have the part numbers of the probes? We might be able to track down specs on them.
 
patroclus said:
sure,

Tektronix 6109 Probe
HP 10441A 500 Mhz

both 10X..

Tektronix 6109 probe, compensation range 15-35 pF. This looks fine.
HP 10441A is a 500MHz bandwidth, 1Meg, 9pF probe, and will only work on scopes that have 1Megohm and 6-9 pF inputs. This won't work on your scope, and I wouldn't buy it if I were you.
 
Thanks.. but, why would the HP probe not work with my scope? If capacitance is lower than scope's, it does not work??
 
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