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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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About them 'scope probes
Finally last night I was able to sit down and figure out the probe
adjustment. I have 5 probes. One 10x Tek probe, one 20x Tek probe, one Probemaster 1x & 10x probe, and two other 1x & 10x probes from China. The 10x Tek and the Probemaster probes are 100 MHz rated and made in the USA. The Tek 20x probe is 200Mhz rated and USA made. The Chinese probes are 100MHz rated. I realized the probes need to be adjusted only in the 10x mode. I didn't know that. That for sure was part of the problem. Looking at signals from my function generator it seemed that the voltage was off. Then I realized that my meter displays the RMS value of the AC signal and the 'scope displays the peak values. I got all the probes to display a nice square wave in the 10x setting. I don't know why I got really weird results before but it may be because I was in my machine shop with CNC machines running. At home with everything quiet all the probes behaved like they were supposed to. At the 10x setting. But with the probes set at 1x the square wave isn't quite square. The 3 probes that have the 1x setting all act the same, with the square wave being slightly distorted. It didn't seem to matter if the 'scope was set to AC or DC coupling. It also didn't matter if the signal being measured came from the 'scope or from the function generator. Is this normal, for the square wave displayed to be perfect in the 10X setting and slightly distorted in the 1X setting? The 'scope is a Tek465B. The 20X probe is a TEK model P5120 The 10X probe is a Tek model P6053B The Probmaster is model 3901-2 The Chinese probes only have a model number-P6100 So, as near as I can tell, the probes are all right, at least they all act the same. But what causes the distorted square wave at the 1x setting? Thanks, Eric |
#2
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About them 'scope probes
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#3
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About them 'scope probes
On Thu, 14 Feb 2019 11:25:53 -0800, wrote:
So, as near as I can tell, the probes are all right, at least they all act the same. But what causes the distorted square wave at the 1x setting? It's caused by the lack of high frequency response (i.e. rise time) in X1 mode. For a typical X10/X1 switchable problem, the frequency response is MUCH higher in X10 than in X1. For example: https://www.tiepie.com/en/usb-oscilloscope/accessories/oscilloscope-probe-250mhz-x1-x10 Notice that the bandwidth is 250MHz in X10 but only 6MHz in X1. This one is closer to what I think you bought: https://www.tiepie.com/en/usb-oscilloscope/accessories/oscilloscope-probe-60mhz-x1-x10 60MHz bandwidth in X10 and 6MHz bandwidth in X1. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#4
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About them 'scope probes
wrote:
So, as near as I can tell, the probes are all right, at least they all act the same. But what causes the distorted square wave at the 1x setting? ** What frequency is your test wave ? About 1kHz is usual. .... Phil |
#6
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About them 'scope probes
On Thursday, February 14, 2019 at 2:17:31 PM UTC-5, wrote:
Finally last night I was able to sit down and figure out the probe adjustment. I have 5 probes. One 10x Tek probe, one 20x Tek probe, one Probemaster 1x & 10x probe, and two other 1x & 10x probes from China. The 10x Tek and the Probemaster probes are 100 MHz rated and made in the USA. The Tek 20x probe is 200Mhz rated and USA made. The Chinese probes are 100MHz rated. I realized the probes need to be adjusted only in the 10x mode. I didn't know that. That for sure was part of the problem. Looking at signals from my function generator it seemed that the voltage was off. Then I realized that my meter displays the RMS value of the AC signal and the 'scope displays the peak values. I got all the probes to display a nice square wave in the 10x setting. I don't know why I got really weird results before but it may be because I was in my machine shop with CNC machines running. At home with everything quiet all the probes behaved like they were supposed to. At the 10x setting. But with the probes set at 1x the square wave isn't quite square. The 3 probes that have the 1x setting all act the same, with the square wave being slightly distorted. It didn't seem to matter if the 'scope was set to AC or DC coupling. It also didn't matter if the signal being measured came from the 'scope or from the function generator. Is this normal, for the square wave displayed to be perfect in the 10X setting and slightly distorted in the 1X setting? The 'scope is a Tek465B. The 20X probe is a TEK model P5120 The 10X probe is a Tek model P6053B The Probmaster is model 3901-2 The Chinese probes only have a model number-P6100 So, as near as I can tell, the probes are all right, at least they all act the same. But what causes the distorted square wave at the 1x setting? Thanks, Eric Cool. Hey Eric, I just want to say that one reason I enjoy sharing whatever small amount of knowledge I have with you, is that you'll always follow up and tell me how it turned out. I wish I had more customers like that. They send me a problem... I send them off a few potential solutions, and then ~1/2 the time I don't hear back. I assume something worked... but I don't which of the three solutions it was, or they made some bone head mistake and are embarrassed. Oh, here's a machinist question for you. When tapping holes in an easy metal, Al 6061 say, with a through hole I've got these 'gun'* taps that shoot the chip out the bottom of the hole. If I'm doing a blind hole is there a tap that shoots the chip back up the tap. (chip may not be the right word.) I tap mostly small stuff 4-40, 6-32, 2-56... in approximate order of usage George H. *gun taps is what I call them, there is a GN on the stem. |
#7
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About them 'scope probes
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#8
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About them 'scope probes
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#9
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About them 'scope probes
On Thu, 14 Feb 2019 13:47:40 -0600, Fox's Mercantile
wrote: On 2/14/19 1:25 PM, wrote: The Chinese probes only have a model number-P6100 That alleges they are clones of the Tek P6100 So, as near as I can tell, the probes are all right, at least they all act the same. But what causes the distorted square wave at the 1x setting? All scopes have a basic input impedance. For a 1:1 probe to "look right" the probe has to match that. Mostly it's a matter of the scopes input stage being properly compensated for the probe's cable. Can this basic input impedence be adjusted? Should it be? Eric |
#11
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About them 'scope probes
On Thu, 14 Feb 2019 16:30:11 -0800, Mike wrote:
On 2/14/2019 11:25 AM, wrote: But with the probes set at 1x the square wave isn't quite square. The 3 probes that have the 1x setting all act the same, with the square wave being slightly distorted. If you emailed your doctor and said, "I feel slightly bad," what diagnostic would you expect? At least describe it in such a way that one could draw an accurate picture from your description. And yes, the time dimension is relevant. What's the output impedance of your function generator? What do you see when you plug the function generator directly into the scope, via what kind of cable? I forgot to write the frequency. The frequency being used was 1KHz at 300 MV, from both the 'scope and the function generator. I only have 1 cable that connects to the function generator, it has a BNC connector at one end and alligator clips at the other end. So at this time I cannot directly connect it to the 'scope, I must use the probes. But the probes are what I was testing and I got the same results no matter where the signal was coming from, as I stated in my original post. The output impedence of the function generator is 50 ohms. If I was able to connect the function generator directly to the 'scope with the proper cable what would this tell me? I guess if the square wave shape was still distorted the same way and the same amount then it would be the 'scope that has the problem? And if the square wave was perfect then it would be the probes causing the distortion. Look, I try to post a question with adequate information. It seems like I'm always leaving something out though. It's not because I'm being lazy or trolling. It's because I miss ****, just like eveyone else. And I don't mind being asked for more info, especially if the reasons for the requested info are listed. This helps me to be more accurate in my replies. And helps me learn, which is why I post questions in the first place. Thanks, Eric |
#12
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About them 'scope probes
In article ,
wrote: Can this basic input impedence be adjusted? Should it be? Sometimes, but that's usually a "service adjustment and repair" sort of thing, not something that one is usually expected to do during normal use. In a lot of scopes there's no adjustment that doesn't require e.g. unsoldering parts. There's enough variation between types of scope, that it's probably most common to have a set of probes for each scope. Pick (and if necessary adjust) the probes to match the input characteristics of the scope, and then don't fiddle with 'em. |
#13
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About them 'scope probes
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#14
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About them 'scope probes
On 2/15/2019 11:34 AM, wrote:
On Thu, 14 Feb 2019 16:30:11 -0800, Mike wrote: On 2/14/2019 11:25 AM, wrote: But with the probes set at 1x the square wave isn't quite square. The 3 probes that have the 1x setting all act the same, with the square wave being slightly distorted. If you emailed your doctor and said, "I feel slightly bad," what diagnostic would you expect? At least describe it in such a way that one could draw an accurate picture from your description. And yes, the time dimension is relevant. What's the output impedance of your function generator? What do you see when you plug the function generator directly into the scope, via what kind of cable? I forgot to write the frequency. The frequency being used was 1KHz at 300 MV, from both the 'scope and the function generator. I only have 1 cable that connects to the function generator, it has a BNC connector at one end and alligator clips at the other end. So at this time I cannot directly connect it to the 'scope, I must use the probes. But the probes are what I was testing and I got the same results no matter where the signal was coming from, as I stated in my original post. The output impedence of the function generator is 50 ohms. If I was able to connect the function generator directly to the 'scope with the proper cable what would this tell me? I guess if the square wave shape was still distorted the same way and the same amount then it would be the 'scope that has the problem? And if the square wave was perfect then it would be the probes causing the distortion. Look, I try to post a question with adequate information. It seems like I'm always leaving something out though. It's not because I'm being lazy or trolling. It's because I miss ****, just like eveyone else. And I don't mind being asked for more info, especially if the reasons for the requested info are listed. This helps me to be more accurate in my replies. And helps me learn, which is why I post questions in the first place. Thanks, Eric And yet, the best description you can give for the observed waveform is "distorted". How can you expect a solution to a problem you won't disclose? At the risk of repeating myself... At least describe it in such a way that one could draw an accurate picture from your description. And yes, the time dimension is relevant. |
#15
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About them 'scope probes
Mike wrote:
At the risk of repeating myself... At least describe it in such a way that one could draw an accurate picture from your description. And yes, the time dimension is relevant. ** Ask "et" to describe a match box. Bet he will struggle and make no sense. ..... Phil |
#16
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About them 'scope probes
SNIP
And yet, the best description you can give for the observed waveform is "distorted". How can you expect a solution to a problem you won't disclose? At the risk of repeating myself... At least describe it in such a way that one could draw an accurate picture from your description. And yes, the time dimension is relevant. Whoops! It looks like the wave is over compensated. So it looks like at the beginning of the flat waveform it has a little peak that then drops down to form a flat line for the rest of the wave. This of course repeats but in the negative direction for the negative part of the wave. I thought you meant frequency for the time dimension but now I think what you mean is how long does it take for the waveform to become flat. It looks like it takes .1 mS. And the overshoot is about 30mV Eric |
#17
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About them 'scope probes
wrote:
But with the probes set at 1x the square wave isn't quite square. The 3 probes that have the 1x setting all act the same, with the square wave being slightly distorted. It didn't seem to matter if the 'scope was set to AC or DC coupling. It also didn't matter if the signal being measured came from the 'scope or from the function generator. ** Now that you have finally DESCRIBED the "distortion" ( a 10% overshoot) the answer is obvious. The 465 scope is the culprit, the vertical attenuator needs frequency adjustment. With the various probes in 10:1 setting, the trim cap allows you to compensate for the error in the scope. ..... Phil |
#18
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About them 'scope probes
On Fri, 15 Feb 2019 11:07:18 -0800, wrote:
On Thu, 14 Feb 2019 13:09:32 -0800, Jeff Liebermann wrote: On Thu, 14 Feb 2019 11:25:53 -0800, wrote: So, as near as I can tell, the probes are all right, at least they all act the same. But what causes the distorted square wave at the 1x setting? It's caused by the lack of high frequency response (i.e. rise time) in X1 mode. For a typical X10/X1 switchable problem, the frequency response is MUCH higher in X10 than in X1. For example: https://www.tiepie.com/en/usb-oscilloscope/accessories/oscilloscope-probe-250mhz-x1-x10 Notice that the bandwidth is 250MHz in X10 but only 6MHz in X1. This one is closer to what I think you bought: https://www.tiepie.com/en/usb-oscilloscope/accessories/oscilloscope-probe-60mhz-x1-x10 60MHz bandwidth in X10 and 6MHz bandwidth in X1. The frequency I was using was 1KHz. That's what the 'scope puts out and what the function generator was set at. With a 100MHz probe shouldn't a 1 KHz signal be low enough to avoid the rise time issue? No. The rise time and bandwidth are not related to the frequency of the input waveform. Basically: Bandwidth * RiseTime = 0.35 https://www.tek.com/support/faqs/how-bandwidth-related-rise-time-oscilloscopes If the rise time of the 1KHz waveform is very small, you will need a probe and scope with a high bandwidth in order to see it. If these are lacking, the scope will display a much slower rise time than what the 1KHz generator is actually producing. For the two scope probes I mentioned above, both probes have 6MHz bandwidth. RiseTime = 0.35 / Bandwidth = 0.35 / 6*10^6 = 0.058 * 10^-6 = 58 * 10^-9 = 58 nsec rise time with an X1 probe. You can also mangle the waveform by setting the vertical amplifier set to AC instead of DC. That will cause the top and bottom of the square wave to sag like a capacitor charge/discharge curve. I can't tell which of these is the problem because your description of the waveform as "really weird results" and "slightly distorted" isn't really sufficient. I didn't even know about the difference in the frequency response. Now, you know. There should be something on the web that covers all this. Search for: https://www.google.com/search?q=analog+oscilloscope+basics EEVblog #453 - Mysteries of x1 Oscilloscope Probes Revealed https://www.youtube.com/watch?v=OiAmER1OJh4 (29:48) ABCs of Probes https://download.tek.com/document/02_ABCs%20of%20Probes%20Primer.pdf See Pg 8, 35-37. Is this one of the reasons that people recommend using the 10X setting unless the 1x setting is needed? Yep. That the only time the 1X setting is used is when the signal needs to be measured un-attenuated? Nope. There are plenty of uses for an X1 probe. If the signal is very low amplitude, it's easier to see using either a direct connection to the scope input or an X1 problem. If the frequency is low enough that you don't care about bandwidth, then X1 is just fine. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#19
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About them 'scope probes
On Fri, 15 Feb 2019 14:56:25 -0800, Jeff Liebermann
wrote: On Fri, 15 Feb 2019 11:07:18 -0800, wrote: On Thu, 14 Feb 2019 13:09:32 -0800, Jeff Liebermann wrote: On Thu, 14 Feb 2019 11:25:53 -0800, wrote: So, as near as I can tell, the probes are all right, at least they all act the same. But what causes the distorted square wave at the 1x setting? It's caused by the lack of high frequency response (i.e. rise time) in X1 mode. For a typical X10/X1 switchable problem, the frequency response is MUCH higher in X10 than in X1. For example: https://www.tiepie.com/en/usb-oscilloscope/accessories/oscilloscope-probe-250mhz-x1-x10 Notice that the bandwidth is 250MHz in X10 but only 6MHz in X1. This one is closer to what I think you bought: https://www.tiepie.com/en/usb-oscilloscope/accessories/oscilloscope-probe-60mhz-x1-x10 60MHz bandwidth in X10 and 6MHz bandwidth in X1. The frequency I was using was 1KHz. That's what the 'scope puts out and what the function generator was set at. With a 100MHz probe shouldn't a 1 KHz signal be low enough to avoid the rise time issue? No. The rise time and bandwidth are not related to the frequency of the input waveform. Basically: Bandwidth * RiseTime = 0.35 https://www.tek.com/support/faqs/how-bandwidth-related-rise-time-oscilloscopes If the rise time of the 1KHz waveform is very small, you will need a probe and scope with a high bandwidth in order to see it. If these are lacking, the scope will display a much slower rise time than what the 1KHz generator is actually producing. For the two scope probes I mentioned above, both probes have 6MHz bandwidth. RiseTime = 0.35 / Bandwidth = 0.35 / 6*10^6 = 0.058 * 10^-6 = 58 * 10^-9 = 58 nsec rise time with an X1 probe. You can also mangle the waveform by setting the vertical amplifier set to AC instead of DC. That will cause the top and bottom of the square wave to sag like a capacitor charge/discharge curve. I can't tell which of these is the problem because your description of the waveform as "really weird results" and "slightly distorted" isn't really sufficient. I didn't even know about the difference in the frequency response. Now, you know. There should be something on the web that covers all this. Search for: https://www.google.com/search?q=analog+oscilloscope+basics EEVblog #453 - Mysteries of x1 Oscilloscope Probes Revealed https://www.youtube.com/watch?v=OiAmER1OJh4 (29:48) ABCs of Probes https://download.tek.com/document/02_ABCs%20of%20Probes%20Primer.pdf See Pg 8, 35-37. Is this one of the reasons that people recommend using the 10X setting unless the 1x setting is needed? Yep. That the only time the 1X setting is used is when the signal needs to be measured un-attenuated? Nope. There are plenty of uses for an X1 probe. If the signal is very low amplitude, it's easier to see using either a direct connection to the scope input or an X1 problem. If the frequency is low enough that you don't care about bandwidth, then X1 is just fine. Thanks Jeff, Below is an answer I gave to Mike about the wave shape and other features. The description should give you a better idea of what I am seeing. At least I hope it does. "Whoops! It looks like the wave is over compensated. So it looks like at the beginning of the flat waveform it has a little peak that then drops down to form a flat line for the rest of the wave. This of course repeats but in the negative direction for the negative part of the wave. I thought you meant frequency for the time dimension but now I think what you mean is how long does it take for the waveform to become flat. It looks like it takes .1 mS. And the overshoot is about 30mV Eric" Thanks Again, Eric |
#20
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About them 'scope probes
Jeff Liebermann wrote:
You can also mangle the waveform by setting the vertical amplifier set to AC instead of DC. That will cause the top and bottom of the square wave to sag like a capacitor charge/discharge curve. ** No sign of that will be seen with a 1kHz square wave. I can't tell which of these is the problem because your description of the waveform as "really weird results" and "slightly distorted" isn't really sufficient. ** That info was posted by the OP 3 or 4 hours ago. You must read all the posts in a thread before posting replies with dumb error like that. ..... Phil |
#21
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About them 'scope probes
On Fri, 15 Feb 2019 15:33:01 -0800, wrote:
Below is an answer I gave to Mike about the wave shape and other features. The description should give you a better idea of what I am seeing. At least I hope it does. "Whoops! It looks like the wave is over compensated. So it looks like at the beginning of the flat waveform it has a little peak that then drops down to form a flat line for the rest of the wave. Under compensated or too little capacitance. The overshoot of the rising part of the square wave means you have too much high frequency response. This of course repeats but in the negative direction for the negative part of the wave. Yep. If the negative going part of the waveform were not identical, then your input square is not symmetrical. I thought you meant frequency for the time dimension but now I think what you mean is how long does it take for the waveform to become flat. No. The flat part of the waveform is the low frequency component, which is independent of the rise time. If the flat part sags, then you are capacitor coupling (AC coupling) somewhere, probably the AC/DC switch on the vertical input. It looks like it takes .1 mS. And the overshoot is about 30mV I can't tell if that means that it sags 0.1msec or the overshoot lasts 0.1msec. Perhaps a posting photo of the screen would be helpful. More reading: "The Secret World of Oscilloscope Probes" http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf The link in the video to EEVblog doesn't work. This does: "EEVblog #453 - Mysteries of x1 Oscilloscope Probes Revealed" http://www.eevblog.com/forum/blog/eevblog-453-mysteries-of-x1-oscilloscope-probes-revealed/?all -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#22
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About them 'scope probes
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#23
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About them 'scope probes
On 2/15/2019 4:15 PM, Phil Allison wrote:
wrote: But with the probes set at 1x the square wave isn't quite square. The 3 probes that have the 1x setting all act the same, with the square wave being slightly distorted. It didn't seem to matter if the 'scope was set to AC or DC coupling. It also didn't matter if the signal being measured came from the 'scope or from the function generator. ** Now that you have finally DESCRIBED the "distortion" ( a 10% overshoot) the answer is obvious. The 465 scope is the culprit, the vertical attenuator needs frequency adjustment. With the various probes in 10:1 setting, the trim cap allows you to compensate for the error in the scope. .... Phil Anyone wanting to store this list of TEKtronix probe characteristics should do it now. The link is no longer functional, I went to the Wayback Machine to locate it. https://web.archive.org/web/20180104...age_probes.asp It has info on about 100 different TEK probes. Mikek |
#24
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About them 'scope probes
On Fri, 15 Feb 2019 19:02:44 -0800, Jeff Liebermann
wrote: On Fri, 15 Feb 2019 15:33:01 -0800, wrote: Below is an answer I gave to Mike about the wave shape and other features. The description should give you a better idea of what I am seeing. At least I hope it does. "Whoops! It looks like the wave is over compensated. So it looks like at the beginning of the flat waveform it has a little peak that then drops down to form a flat line for the rest of the wave. Under compensated or too little capacitance. The overshoot of the rising part of the square wave means you have too much high frequency response. This of course repeats but in the negative direction for the negative part of the wave. Yep. If the negative going part of the waveform were not identical, then your input square is not symmetrical. I thought you meant frequency for the time dimension but now I think what you mean is how long does it take for the waveform to become flat. No. The flat part of the waveform is the low frequency component, which is independent of the rise time. If the flat part sags, then you are capacitor coupling (AC coupling) somewhere, probably the AC/DC switch on the vertical input. It looks like it takes .1 mS. And the overshoot is about 30mV I can't tell if that means that it sags 0.1msec or the overshoot lasts 0.1msec. Perhaps a posting photo of the screen would be helpful. More reading: "The Secret World of Oscilloscope Probes" http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf The link in the video to EEVblog doesn't work. This does: "EEVblog #453 - Mysteries of x1 Oscilloscope Probes Revealed" http://www.eevblog.com/forum/blog/eevblog-453-mysteries-of-x1-oscilloscope-probes-revealed/?all Thanks again Jeff. I have watched EEVblog several times and haven't had time yet to check out completely the episode mentioned. I looked for it and just got it started when the dryer belt broke. Anyway, when I spoke above about .1mS I meant that the overshoot lasts that long. So there is a peak at the beginning of the square wave and then the trace curves down to become flat. And the time it takes to become flat is about .1 mS. The computer I am posting from is running XP and so I can't use Dropbox. I should look for another easy to post to picture site. Eric |
#25
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About them 'scope probes
On Fri, 15 Feb 2019 19:02:44 -0800, Jeff Liebermann
wrote: On Fri, 15 Feb 2019 15:33:01 -0800, wrote: Below is an answer I gave to Mike about the wave shape and other features. The description should give you a better idea of what I am seeing. At least I hope it does. "Whoops! It looks like the wave is over compensated. So it looks like at the beginning of the flat waveform it has a little peak that then drops down to form a flat line for the rest of the wave. Under compensated or too little capacitance. The overshoot of the rising part of the square wave means you have too much high frequency response. This of course repeats but in the negative direction for the negative part of the wave. Yep. If the negative going part of the waveform were not identical, then your input square is not symmetrical. I thought you meant frequency for the time dimension but now I think what you mean is how long does it take for the waveform to become flat. No. The flat part of the waveform is the low frequency component, which is independent of the rise time. If the flat part sags, then you are capacitor coupling (AC coupling) somewhere, probably the AC/DC switch on the vertical input. It looks like it takes .1 mS. And the overshoot is about 30mV I can't tell if that means that it sags 0.1msec or the overshoot lasts 0.1msec. Perhaps a posting photo of the screen would be helpful. More reading: "The Secret World of Oscilloscope Probes" http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf The link in the video to EEVblog doesn't work. This does: "EEVblog #453 - Mysteries of x1 Oscilloscope Probes Revealed" http://www.eevblog.com/forum/blog/eevblog-453-mysteries-of-x1-oscilloscope-probes-revealed/?all Greetings Jeff, Well, I watched that video you mentioned plus another two, one put out by Tektronix. I now understand WAY better what's going on. Thanks for the link and suggestions. I know it shouldn't matter but the EEVblog guy's voice bugs me. But his explanation was clear. And the pdf you posted a link to was also very educational. Thanks, Eric |
#26
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About them 'scope probes
On Tue, 26 Feb 2019 12:16:27 -0800, wrote:
On Fri, 15 Feb 2019 19:02:44 -0800, Jeff Liebermann wrote: More reading: "The Secret World of Oscilloscope Probes" http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf The link in the video to EEVblog doesn't work. This does: "EEVblog #453 - Mysteries of x1 Oscilloscope Probes Revealed" http://www.eevblog.com/forum/blog/eevblog-453-mysteries-of-x1-oscilloscope-probes-revealed/?all Well, I watched that video you mentioned plus another two, one put out by Tektronix. I now understand WAY better what's going on. Thanks for the link and suggestions. I know it shouldn't matter but the EEVblog guy's voice bugs me. But his explanation was clear. And the pdf you posted a link to was also very educational. Thanks, Eric Y'er welcome. There's also a mess of magic (and confusion) with high voltage probes, where the frequency response varies with the applied voltage. See graph on Pg 1-12: https://download.tek.com/manual/070822305.pdf Also active probes that work at GHz frequencies with input loading around 1M and 1pf. You can really get spoiled with those working around RF. "Active probes: why they are worth buying" https://www.eetimes.com/document.asp?doc_id=1279659# I have the same problem with Dave Jones of EEVblog. Recently, he's made an attempt to shorten his videos and clean up his presentation, but it's still difficult viewing. Here's a clue: https://www.youtube.com/user/EEVblog "No Script, No Fear, All Opinions" Methinks a script and an editor might help. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#27
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About them 'scope probes
On 2/26/2019 1:29 PM, Jeff Liebermann wrote:
On Tue, 26 Feb 2019 12:16:27 -0800, wrote: On Fri, 15 Feb 2019 19:02:44 -0800, Jeff Liebermann wrote: More reading: "The Secret World of Oscilloscope Probes" http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf The link in the video to EEVblog doesn't work. This does: "EEVblog #453 - Mysteries of x1 Oscilloscope Probes Revealed" http://www.eevblog.com/forum/blog/eevblog-453-mysteries-of-x1-oscilloscope-probes-revealed/?all Well, I watched that video you mentioned plus another two, one put out by Tektronix. I now understand WAY better what's going on. Thanks for the link and suggestions. I know it shouldn't matter but the EEVblog guy's voice bugs me. But his explanation was clear. And the pdf you posted a link to was also very educational. Thanks, Eric Y'er welcome. There's also a mess of magic (and confusion) with high voltage probes, where the frequency response varies with the applied voltage. See graph on Pg 1-12: https://download.tek.com/manual/070822305.pdf That has nothing to do with the frequency response. Probes are VOLTAGE derated with frequency. Think about it... At infinite frequency, all the caps look like shorts and it lets the smoke out. Also active probes that work at GHz frequencies with input loading around 1M and 1pf. You can really get spoiled with those working around RF. "Active probes: why they are worth buying" https://www.eetimes.com/document.asp?doc_id=1279659# I have the same problem with Dave Jones of EEVblog. Recently, he's made an attempt to shorten his videos and clean up his presentation, but it's still difficult viewing. Here's a clue: https://www.youtube.com/user/EEVblog "No Script, No Fear, All Opinions" Methinks a script and an editor might help. |
#28
Posted to sci.electronics.repair
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About them 'scope probes
wrote:
I got all the probes to display a nice square wave in the 10x setting. But with the probes set at 1x the square wave isn't quite square. You got lots of answers in this 1.5 year old thread, but the group seems to have missed one explanation that might make sense to you. Someone posted the bandwidth of two different probes in 1x mode, and that bandwidth was 6Mhz. A square wave can be represented as an infinite sum of sine waves, one sine wave at the base frequency, and every odd harmonic of that base sine wave up to infinity. See: https://en.wikipedia.org/wiki/Square...urier_analysis Your probes, when in 1x mode, are acting as low pass filters, with a -3db point at the 6Mhz bandwidth of the probe. So for the input square wave, consisting of an infinite sum of odd harmonics, the 1x probe is filtering away most of the harmonics above 6Mhz. When you low pass filter away most of the higher frequency harmonics that sum to create a square wave, what you have left is a *distorted* square wave. |
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