Advice oscilloscope for (mainly) floating measuring

Thread Starter

Teris

Joined Nov 4, 2017
29
Hello,
I am consider to buy a oscilloscope. My needs is mainly for floating measuring maximum 50Mhz and 330Vpeak.
What of oscilloscope do you advice for that job?
I read that "difference function" from MATH of bench oscilloscope is not efficient method. This is this true?
 

dl324

Joined Mar 30, 2015
11,231
My needs is mainly for floating measuring maximum 50Mhz and 330Vpeak.
What of oscilloscope do you advice for that job?
Since you have to ask, I suggest that you use a battery powered scope.
I read that "difference function" from MATH of bench oscilloscope is not efficient method. This is this true?
Don't know why that would be the case. Can you cite some references?
 

tautech

Joined Oct 8, 2019
123
Hello,
I am consider to buy a oscilloscope. My needs is mainly for floating measuring maximum 50Mhz and 330Vpeak.
What of oscilloscope do you advice for that job?
The ordinary bench DSO of your choice plus a differential probe and the reason is better versatility and feature set than a handheld scope.
I read that "difference function" from MATH of bench oscilloscope is not efficient method. This is this true?
Yes, there are limits to the 2 probe and Math method due to issues with CMRR.
Have a read of the section on Differential Probes P17 in this Tek ABC of Probes:
http://web.mit.edu/6.101/www/reference/ABCprobes_s.pdf
 

tautech

Joined Oct 8, 2019
123
The measuring accuracy different between differential probe and Math method is visible or can be 1-2% error?
Did you even read and study the pages specified in the link i found for you ?
For your convenience I'll paste it for you, study it, especially highlighted parts.

Using two probes to make two single-ended measurements, as shown in Figure 2.4a is an often used method. It’s also usually the least desirable method of making differential measurements. Nonetheless, the method is often used because a dual-channel oscilloscope is available with two probes. Measuring both signals to ground (single-ended) and using the oscilloscope’s math functions to subtract one from the other (channel A signal minus channel B) seems like an elegant solution to obtaining the difference signal. And it can be in situations where the signals are low frequency and have enough amplitude to be above any concerns of noise. Primer 18 www.tektronix.com/accessories There are several potential problems with combining two single-ended measurements. One problem is that there are two long and separate signal paths down each probe and through each oscilloscope channel. Any delay differences between these paths results in time skewing of the two signals. On high-speed signals, this skew can result in significant amplitude and timing errors in the computed difference signal. To minimize this, matched probes should be used. Another problem with single-ended measurements is that they don’t provide adequate common-mode noise rejection. Many low-level signals, such as disk read channel signals, are transmitted and processed differentially in order to take advantage of common-mode noise rejection. Commonmode noise is noise that is impressed on both signal lines by such things as nearby clock lines or noise from external sources such as fluorescent lights. In a differential system this common-mode noise tends to be subtracted out of the differential signal. The success with which this is done is referred to as the common-mode rejection ratio (CMRR). Because of channel differences, the CMRR performance of single-ended measurements quickly declines to dismal levels with increasing frequency. This results in the signal appearing noisier than it actually would be if the common-mode rejection of the source had been maintained. A differential probe, on the other hand, uses a differential amplifier to subtract the two signals, resulting in one differential signal for measurement by one channel of the oscilloscope (Figure 2.4b). This provides substantially higher CMRR performance over a broader frequency range.

I've offered a recommendation previously as a bench DSO and differential probe/s is the best choice and offers the best versatility for accurate measurement. While we would all like the availability of cheap isolated channels DSO's with a wealth of functionality there are no such beats in existence yet some imagine a handheld DSO offers the magic bullet however unless it offers truly isolated channels and not BNC shell commoned like most are they are not the solution either.

Differential probes added to a bench scope are the most cost effective and safe solution, bar none.

Come back and tell us what you might select as a solution if you need further advice.
 

Thread Starter

Teris

Joined Nov 4, 2017
29
Thank you very much for your information. Now i understand that there is not absolute error from Math method, but is depending the frequency. About the oscilloscope i would like one from first class brands. In the case of differential probe can i trust any cheapest or worth to spend more money for first class brand? I ask this because are expensive.
 

tautech

Joined Oct 8, 2019
123
Thank you very much for your information. Now i understand that there is not absolute error from Math method, but is depending the frequency. About the oscilloscope i would like one from first class brands.
Why ? Really why ?
Specs and capability of an apples vs apples model are no better than many B brands which are somewhat cheaper and just as reliable.
An indication of your budget constraints can allow suggestion of very reasonably priced models that will fit most needs.
In the case of differential probe can i trust any cheapest or worth to spend more money for first class brand? I ask this because are expensive.
Well for this I've picked Diff probes from well know manufactures that have been making them for a good while so their datasheet spec can be trusted. There are a good few differential probe manufacturers and some supply scope manufacturers and have their products rebadged however when this happens another level of price markup is added and pushes costs upwards unnecessarily.

It's entirely dependent on your location what you can access and what local sellers decide to stock.
As some example I source the Pintek range (not Pintech) from Taiwan as they're good value for money.
Hunt for them locally and you should be able to find someone stocking them.
http://www.pintek.com.tw/product_classify/landersound-tail/index.php?Product_Site_Classify_SN=17072&PHPSESSID=5ubfkn4vbbie2hnjkpk2r07am6&Company_SN=6002
 

ronsimpson

Joined Oct 7, 2019
811
I have a battery powered scope. Looks much like this one. Probably not the same. While charging or connected to a USB-PC port it can float to 3kv. All the connections and probes are double insulated so you will not get hurt by douching the scope when the ground probe is not at ground.
1596836678686.png
One of the dangers of floating a normal scope is that the knobs and probes are not at ground and can kill you. I often connect this scope to the hot side of the power line. Mine is only 20mhz but lives very well at 220vac or 440vac. Just remember that while the "ground" for a probe is not connected to ground; Probe-1 ground is connected to Probe-2 ground!
 

strantor

Joined Oct 3, 2010
5,322
Do not buy a Fluke Scopemeter based on the idea of it being a "first class brand." In multimeters, they are king. In oscilloscopes, well... it's like when an actor starts a clothing line or when a clothing designer starts a perfume/cologne line. Being good at one thing does not mean being good at something else.
 

Thread Starter

Teris

Joined Nov 4, 2017
29
An indication of your budget constraints can allow suggestion of very reasonably priced models that will fit most needs.
I am consider about 800-1000€ for oscilloscope. Keysight new DSOX1202A or used like DSOX2012A on ebay with 825€.
 

tautech

Joined Oct 8, 2019
123
I am consider about 800-1000€ for oscilloscope. Keysight new DSOX1202A or used like DSOX2012A on ebay with 825€.
Oh KS, did you know that in their class and with their capabilities they have a relatively small memory depth ?
It does not matter for some users however it limits the real power of a DSO; capture memory depth.

10+ MPts is much better if you need to capture any significant sequence of events.
In the same class is the 200 MHz SDS2202X-E which is a bit cheaper yet has some better features.
Another step up in capability and features is SDS2102X Plus or one of its 4ch brothers that gives any of the A brands a good run for their money.

We are actually spoilt for choice with DSO's today such has been the advances of the B brands in the last few years.
Good luck with your selection.
 

rsjsouza

Joined Apr 21, 2014
253
One of the dangers of floating a normal scope is that the knobs and probes are not at ground and can kill you.
Yes, 100%. Tautech's solution for a differential probe is more sensible than floating either the scope or the equipment under test.
However, unless you really need portability, the handheld models have typically lower specifications when compared to a bench oscilloscope of comparable price.

I am consider about 800-1000€ for oscilloscope. Keysight new DSOX1202A or used like DSOX2012A on ebay with 825€.
Keysight's DSOX1000 series are newer, but, unless you really need the 200MHz of bandwidth, you could try to save some money and get the DSOX1102A, perhaps?

Also, as Tautech aluded, the Keysight's offers are much less featured than the typical B brands Siglent, Rigol and GW Instek, which can be had for much less money and still with quite decent usability and reliability. I am thinking about the Siglent SDS1202X-E, the Rigol DS1202Z-E and the GW Instek GDS-1072B. Obviously all that is thrown out of the equation depending on the local availability for your region.
 

Thread Starter

Teris

Joined Nov 4, 2017
29
Almost everyone says that A class brands are less featured than cheaper brands. I always have the question why the A class brands don't upgrade their models, specifications as memory depth, and keep them lower. It's so expensive to improve them?
At this category of oscilloscopes, what is the advantage of first class brands in their oscilloscopes? There is no point that excels?
 

tautech

Joined Oct 8, 2019
123
Almost everyone says that A class brands are less featured than cheaper brands.
Features is a very wide term and one must decide what features matter to them or whether the overall feature set is of greater importance. No longer is a scope just a scope but a box full of instruments in just one case which can result in less clutter on the bench which often for the novice, even the semi-pro can mean just one spend instead of multiples.
I always have the question why the A class brands don't upgrade their models, specifications as memory depth, and keep them lower. It's so expensive to improve them?
They mostly feel they don't need to as they have a big enough followings and as always ongoing competition from their A brand peers so worry less of the B brands nipping at their heels.
Improvements take time and resources that the B brands are keener to invest to get a slice of the pie along with some novel feature developments in recent years that are rightfully turning heads so to compete on features against the A brands.
Here we need look at the scope design itself, be it ADC or ASIC based and their strategies of memory management to maintain high update rates which is where ASIC's shine with relatively low memory depths used so to not impact on update rate.
But there are other ways to skin the same cat like ADC's supported with deep memory continually refreshed history buffers and sequential memory.
The modern scope is a DSO and its strength among numerous other things is waveform capture where deep memory is most desirable to take full advantage by allowing greater analysis of the event capture. If we consider sampling rate vs mem depth we get the full picture of a scopes worth when it comes to capture length in s/div.
Todays modern scope is a complex beast that takes a full week or more to get to know properly in order to get the best from it.

At this category of oscilloscopes, what is the advantage of first class brands in their oscilloscopes? There is no point that excels?
Some say support others say reliability however from where I sit B brands offer good value for your spend.
 

rsjsouza

Joined Apr 21, 2014
253
Tautech's points are very sensible, with a few additional clarifications:
- the only ASIC-based oscilloscope in the entry level is the Keysight. All others are based on FPGAs, which grants more flexibility to add several features including the amount of built-in high speed storage memory - an important aspect if you feel that you may need to capture a long sequence of waveforms to detect a problem (could also be called a "history" of your measurement) and you need to "Zoom In" and still be able to see its details. Typically, the longer the storage memory, the better. In this important feature alone, the Keysight loses to the other brands by a factor of about 10x, although it can partially compensate by other means. Additional details about acquisition systems can be found at:
https://www.testandmeasurementtips.com/memory-depth-and-sampling-rate-in-oscilloscopes/

- as he mentioned, oscilloscopes aggregate several functions to ease the process of performing wave analysis, such as addition and subtraction operations (to remove noise, for example) and frequency domain analysis (FFT, to see how "pure" a sinusoidal is, among other things) and plain numerical measurements (average, RMS, amplitude, peak-to-peak, etc). Of these, the oscilloscopes differ the most in the function that demands the most of its internal processor: the accuracy/sharpness of the FFT, described as the number of "points" or "bins".
- another aggregated function that differs across the board is regarding to digital serial protocol decoding. That does not seem to be a concern for you but the B brands tend to have more protocols available. Given this is a function that demands a lot from the built-in processor, it tends to be better implemented on newer models and A brands.

Some say support others say reliability however from where I sit B brands offer good value for your spend.
At this price point, the A brands do not offer much more than B brands, thus the lines are much more blurred.
 

tautech

Joined Oct 8, 2019
123
Tautech's points are very sensible, with a few additional clarifications:
- the only ASIC-based oscilloscope in the entry level is the Keysight.
There's another but in the upper entry level class.
To date the MSO5000 seems to suffer from processing latency of the deep memory it offers. Maybe they'll get on top of this but after nearly 2 years since release it's not obvious they will.
 

rsjsouza

Joined Apr 21, 2014
253
There's another but in the upper entry level class.
To date the MSO5000 seems to suffer from processing latency of the deep memory it offers. Maybe they'll get on top of this but after nearly 2 years since release it's not obvious they will.
Yeah, I was trying to avoid getting to the DS5000 series as it is a tick above entry level.
 
Hi all. I'm not even a newbie, more of a sub-newbie, an older guy who has decided to take on the venture of learning something about electronics - I'm taking a class. Anyhow, I'm definitely not in the market for an osc yet (not even certain how one works completely) I'm still learning to use my MM a little better, but I've been window shopping a bit lately and maybe down the road I'll grab one when/if I decide it might be a useful (justifying the cost) tool. I've been reading this thread trying to gain a little education on the subject and just wanted to say thanks.

I guess I'm planning on tinkering a bit in my shop and maybe doing some light repairs eventually and thought a scope might be a nice tool to have (and a fun toy). I'm older and by no means wealthy or anything but I do have a little play money and once I know a little more what I'm doing I may get one down the road. I figure another reason for it, if the woman comes into the shop to pester me about trivial matters like mowing the lawn, fixing the gutters, etc., instead of thinking I'm just doing my silly little electronics stuff, if she sees this fancy-looking high tech gadget with a sine wave and asks what I'm doing, and I can give a reply like "I'm running a circuit test on the second frequency trying to determine if this capacitor is compatible with the rectifier, or do I have to override it with a step-down transformer. It's going to be a while, what's up"? Maybe she'll be less-likely to interrupt me to take out the trash... so that's an added bonus.

Anyhow, I've been looking a little on Amazon and saw a Siglent with some good reviews. I don't want to spend 360 on a scope and down the road wished I'd spent the 500 so I'm still looking and will be for some time. I'll keep reading some threads, etc., and once I know a little more I'll decide if and what... I don't want a "beginner" model and have to upgrade later, but I also don't want to blow up a $500 piece of equipment on my first outing either. Either way, at this point, I'm just looking.

Just wanted to say thanks and after reading a few threads on this site, that you all are some smart, knowledgeable dudes - a great resource here.

Take care,
Tim
 

strantor

Joined Oct 3, 2010
5,322
I have a tektronix 2430A scope that I haven't used in years. It worked fine last i used it. I took it out a few days ago for a demonstration, plugged it in and it puked a capacitor. It shows some failed self tests now. You can have it if you want to pay for shipping. It would be a good first scope and a good exercise in circuit repair. I wont be offended if you decline. I might decline myself, thinking I would need a working scope to troubleshoot a broken one. But as far as I know, there's only a bad cap and it should be obvious which one, once you get it open (I havent opened it)

I have no idea why this post is in italics
 
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