Products > Test Equipment
Is 10x more accurate than 1x?
tggzzz:
--- Quote from: schmitt trigger on October 30, 2023, 02:47:39 am ---Also, it goes without saying, that probing a hi-Z circuit node with a 1X probe will load it much more (and therefore have a larger error) than probing it with a 10X probe.
--- End quote ---
What's the tip impedance of a 10Mohm//15pF probe at 250MHz?
What's the tip impedance of a 50ohm *1 Z0 probe at 250MHz?
Hint: the high impedance probe isn't high impedance!
tggzzz:
--- Quote from: rg2113 on October 30, 2023, 02:19:55 am --- I can see jitter with the probe set to 10x versus the 1x probe.
--- End quote ---
Ringing, not jitter.
To understand what's happening, see https://entertaininghacks.wordpress.com/2016/09/17/scope-probe-accessory-higher-frequency-results/
To learn more about probes and how they interact with the UUT, see the references at https://entertaininghacks.wordpress.com/scope-probe-reference-material/
schmitt trigger:
--- Quote from: tggzzz on October 30, 2023, 08:52:13 pm ---
--- Quote from: schmitt trigger on October 30, 2023, 02:47:39 am ---Also, it goes without saying, that probing a hi-Z circuit node with a 1X probe will load it much more (and therefore have a larger error) than probing it with a 10X probe.
--- End quote ---
What's the tip impedance of a 10Mohm//15pF probe at 250MHz?
What's the tip impedance of a 50ohm *1 Z0 probe at 250MHz?
Hint: the high impedance probe isn't high impedance!
--- End quote ---
The TS is obviously asking a newbie question, which MOST likely means a performance comparison between the ubiquitous 10X/1X probes. He wasn’t never asking for a performance comparison to a 50 ohm probe or any other types of probes.
Since a 10X probe is typically (10M || 15p) and a 1X probe is (1M || 60p or more) my answer is still valid.
tggzzz:
--- Quote from: schmitt trigger on October 31, 2023, 01:37:50 am ---
--- Quote from: tggzzz on October 30, 2023, 08:52:13 pm ---
--- Quote from: schmitt trigger on October 30, 2023, 02:47:39 am ---Also, it goes without saying, that probing a hi-Z circuit node with a 1X probe will load it much more (and therefore have a larger error) than probing it with a 10X probe.
--- End quote ---
What's the tip impedance of a 10Mohm//15pF probe at 250MHz?
What's the tip impedance of a 50ohm *1 Z0 probe at 250MHz?
Hint: the high impedance probe isn't high impedance!
--- End quote ---
The TS is obviously asking a newbie question, which MOST likely means a performance comparison between the ubiquitous 10X/1X probes. He wasn’t never asking for a performance comparison to a 50 ohm probe or any other types of probes.
Since a 10X probe is typically (10M || 15p) and a 1X probe is (1M || 60p or more) my answer is still valid.
--- End quote ---
The newbie almost certainly doesn't realise that the tip impedance of one of his "high" impedance probes is ~40ohms at 250MHz.
If he is interested in "accuracy" then he should start to think about how that probe will affect the UUT.
Once he thinks about that, he would probably want to find ways of reducing the problem, and a Z0 probe is a quick and easy way of doing it. All you need are a couple of resistors and a piece of coax. Easy to make at home, unlike a "high" impedance probe.
magic:
Most likely neither of the results you have shown is correct.
1x mode is definitely too slow for this signal.
10x mode has overshoot and ringing which were likely caused by improper grounding of the probe. The bundled alligator clip cable is too long for fast signals, you need to remove the hook tip hood, attach a short wire to the ground contact on the probe and ground it to the board very close to the signal you are probing.
These probes are a pain to use properly to their full potential. IME 100x are much more forgiving of sloppy grounding.
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