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

Reply to
etpm
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That alleges they are clones of the Tek P6100

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.

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Jeff-1.0 
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Reply to
Fox's Mercantile

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: Notice that the bandwidth is 250MHz in X10 but only 6MHz in X1. This one is closer to what I think you bought:

60MHz bandwidth in X10 and 6MHz bandwidth in X1.
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Jeff Liebermann     jeffl@cruzio.com 
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Reply to
Jeff Liebermann

** What frequency is your test wave ?

About 1kHz is usual.

... Phil

Reply to
Phil Allison

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?

Reply to
Mike

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.
Reply to
ggherold

GN for Gun Nose.

You want a spiral flute tap, see pictures here:

Clifford Heath.

Reply to
Clifford Heath

The taps that direct the chips back out of the hole are called high spiral taps. Spiral point taps, AKA gun taps, eject the chips ahead of the tap. I use high spiral taps a lot but I don't like them. They are weaker than spiral point taps. I know, the terminology is confusing, especially since the high spiral taps are actually high helix taps. For blind holes in ductile materials, such as wrought aluminum and mild steel, I like to use roll form taps, AKA form taps, AKA roll taps. In fact, I use roll taps whenever I can because of the stronger thread and because no chips are generated. These taps require a larger hole and hole size must be controlled well because the tap just displaces the metal. With a roll tap you can tap right down to the bottom of a hole because there are no chips generated. Because form taps displace the material the thread is stronger than a cut thread. Virtually all the fasteners you will find in your local hardware store will have formed threads. Materials that can be roll or form tapped include all the wrought aluminum alloys, such as 6061, 6063, 5052, etc. Mild steel, 1144 steel (stressproof), 12L14 steel (leadloy) and 303 stainless steel also tap well with form taps. 304 and 316 can be form tapped but great care must be taken to avoid broken taps. Tap life will also be short in 304 and 316. But if you need threads all the way to the bottom and want to do it in one pass roll taps can work. Materials that should not be formed tapped are the cast aluminum alloys, half hard brass, cast iron, and the like. This is because the material is not ductile and the resulting thread will have tiny fractures, resulting in a weak thread. I have tapped thousands of holes with 2-56 form taps. Always use cutting oil when drilling and tapping holes, never motor oil. Using motor oil leads to broken taps and bad finishes and poor tool life. Hope that helped. Eric

Reply to
etpm

Can this basic input impedence be adjusted? Should it be? Eric

Reply to
etpm

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? I didn't even know about the difference in the frequency response. Is this one of the reasons that people recommend using the 10X setting unless the 1x setting is needed? That the only time the 1X setting is used is when the signal needs to be measured un-attenuated? Thanks, Eric

Reply to
etpm

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 shit, 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

Reply to
etpm

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.

Reply to
Dave Platt

Helped yes.. thanks. I don't do much tapping.. and all of that by hand on the mill. (with starter drill in the chuck, centering the hand tap.) I looked at those spiral taps and thought.. 'dang I'm just going to bust on of those.' I never heard of form taps, but I'll look into them.

Thanks again, George

Reply to
ggherold

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.

Reply to
Mike

** Ask "et" to describe a match box.

Bet he will struggle and make no sense.

.... Phil

Reply to
Phil Allison

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
Reply to
etpm

** 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

Reply to
Phil Allison

No. The rise time and bandwidth are not related to the frequency of the input waveform. Basically: Bandwidth * RiseTime = 0.35 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.

Now, you know. There should be something on the web that covers all this. Search for:

EEVblog #453 - Mysteries of x1 Oscilloscope Probes Revealed (29:48)

ABCs of Probes See Pg 8, 35-37.

Yep.

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.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

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

Reply to
etpm

** No sign of that will be seen with a 1kHz square wave.

** 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

Reply to
Phil Allison

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