Help me pick an o-scope, $3k budget - Page 1
Forum section: electronics / testgear

author: CraftyAndy
author_rank: Newbie
timestamp: August 20, 2018, 06:38:32 pm
content: Hi there,I'm looking to purchase an oscilloscope and would like some input.Here's what I'm planning on measuring:1) Relatively high voltage (>60vdc), and high current (>200A)2) Relatively slow signals3) rs-232 or CAN decoding4) Would like 4 channelsOther considerations:1) May be used in a manufacturing environment where calibration certificates are needed2) I don't mind a headless option (PicoScope grade), as I am very comfortable using my laptop for this3) $3k (USD) budget for scope + all accessories needed for high voltage and currentMy top choice right now is shown in the attached image below, it winds up being ~$2k (USD) and I believe it accomplishes everything I want and sets me up with a nice base unit if I wind up needing more differential inputs. I'm not sure if I'll have the resolution I want with the 25:1 differential probe and a ~60vdc signal, but with the leftover money I could get another one of their probes (70/700v differential probes are available)I see a lot of people suggesting to not go the headless route, which I understand, but I'm curious given my requirements and considerations if this is my best option, or if there's another option out there that'd be better.I may be open to used, but would need it to be from a reputable source in case there are issues or calibrations that need to be redone.Thank you for any input!

author: Andreas
author_rank: Super Contributor
timestamp: August 20, 2018, 08:16:03 pm
content: Hello,If the application is automotive: why not use a PicoScope 4425 with up to +/-200V direct inputs?Probably you will not need any 10:1 or 25:1 probes.The PS4444 is more for mains voltage/motor control development.with best regardsAndreas

author: CraftyAndy
author_rank: Newbie
timestamp: August 20, 2018, 08:26:14 pm
content: Not automotive strictly, rather high power brushless motor test and development. The 4425 does look interesting, and some of the kits come with what I'd want. I didn't see the 4425 as it's down in the "automotive" section, rather than the general oscope section, thank you for the suggestion!I'd assumed there would be more people advocating for a unit with a screen.

author: fonograph
author_rank: Frequent Contributor
timestamp: August 20, 2018, 08:40:22 pm
content: I would go for used Keysight/Agilent 3000X series,the one without touchscreen.They can be hacked to unlock full bandwidth.

author: tautech
author_rank: Super Contributor
timestamp: August 20, 2018, 08:59:47 pm
content: Hmmm, your understanding of calibration tractability might need updating. Most new modern equipment comes with a Cal cert listing the equipment used, their individual SN#'s and the dates that each of their calibration's expire.Further calibration checks areverificationthat the instrument still meets either datasheet spec or the performance specification listed in the service manual. These comparatively simple checks can be done in most Cal labs with just calibrated voltage and frequency sources and a Cal verification is issued.As most modern equipment is 'closed case' calibrated/adjusted it's more important that your local Cal lab has the specifiedorequivalent equipment to undertake adjustments should any be necessary to bring an instrument back into spec.Then to be completely sure of your 'system', current and differential probes need be checked as meeting spec too.What you require doesn't appear to be demanding at all and many cheap entry level scopes could achieve your requirements and at considerable cost savings. If current measurements are required to be accurate this is where I'd be looking for improvements in choice of equipment. What are the current measurement requirements ? AC, DC or both ? Frequency ?

author: CraftyAndy
author_rank: Newbie
timestamp: August 20, 2018, 09:07:54 pm
content: Quote from: fonograph on August 20, 2018, 08:40:22 pmI googled a bit and didn't find much about this option, are you able to elaborate?Quote from: tautech on August 20, 2018, 08:59:47 pmI agree, I come from a background where calibration has not been important, and am now in a position where it is. I don't know what it is other than "calibration". I wasn't sure if this meant certificates, or actual tweaking of pot's to get the measurement to line up with reality. It sounds like it's typically more on the certificates side of things.The currents are both AC and DC (AC at motors, DC at battery). Low frequency on the AC, but will be interested in viewing transient events on the power bus.Thank you both for your input and assistance!

author: tautech
author_rank: Super Contributor
timestamp: August 20, 2018, 09:18:28 pm
content: Quote from: CraftyAndy on August 20, 2018, 09:07:54 pmSo you properly understand, there are zero physical adjustments for Cal procedures in modern equipment.Download a service manual or two and study the required procedures.QuoteThis is where you can spend your entire budget on a good AC/DC current probe and the primary reason why I say most entry level DSO's and especially those with good remote connectivity capability can save you a bundle of cash to spend on the bits that really matter to obtain accurate results.

author: CraftyAndy
author_rank: Newbie
timestamp: August 20, 2018, 09:37:35 pm
content: QuoteI understand that now, I knew it was a possibility previously but wasn't certain. Once I determine which scope I'll be purchasing I'll be reading the manual (and service manual) cover to cover unless you suggest it's a good practice to do prior to purchasingQuoteThat's the kind of information I'm here to gather. I'm not sure if I'm on the right track with my picoscope cart above, or if I should be considering something different. It sounds like the measurements I'm trying to make lead to a low end-scope with high end probes, is that an accurate summary in your opinion?Thanks!

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 20, 2018, 09:39:30 pm
content: Quote from: CraftyAndy on August 20, 2018, 06:38:32 pmsince you ask opinion and you havent ban me... no its not the best choice. i wouldnt waste my money on PicoScope i smell blood sucking brand there. if you are happy to carry around automotive your laptop and the usb scope and dangling wires on your rib then carry on, i'll buy hantek (or migsig?) portable/handheld dso for that purpose. i'll save most of the money in the list, even my rigol DS1054Z can do your requirement. the wisest thing on your list is just the current (or/and he differential) probe, whats not wise about them is their D9 connector.

author: tautech
author_rank: Super Contributor
timestamp: August 20, 2018, 09:51:00 pm
content: Quote from: CraftyAndy on August 20, 2018, 09:37:35 pmYep......well sort of.Current probe AC frequency requirements will dictate what you have to spend along with the resolution/accuracy required.As Mech points out more looking/research is needed.

author: CraftyAndy
author_rank: Newbie
timestamp: August 20, 2018, 09:51:51 pm
content: Quote from: Mechatrommer on August 20, 2018, 09:39:30 pmI've seen a lot of people suggest the Rigol DS1054Z, that's one of the things that caused me to pause before hitting the "buy" button and come consult some people with more knowledge than I on this subject.Thank you for your input!

author: CraftyAndy
author_rank: Newbie
timestamp: August 20, 2018, 10:07:39 pm
content: QuoteThe TA301 ammeter attachment has a 20khz frequency perhttp://www.farnell.com/datasheets/2265784.pdf?_ga=2.27976124.1645628915.1534802263-1531057897.1534802263With motor speeds in the 100Hz range this seems reasonable to view the AC into the motor, as well as transients in the DC bus.The TA301 in the 200A range setting should do fairly well for us in most all situations. Only rarely would we bump it to the 2000A range where we may be losing some resolution.Looking at Rigol accessories, they didn't appear to have probes for the 1000 series that were a great fit for my needs.Thanks again for your input!

author: TK
author_rank: Super Contributor
timestamp: August 20, 2018, 10:08:57 pm
content: The micsig TO1104 in tablet format with touch screen is a good option. It has 4 channels, 100MHz and if you buy the full option for around $500, you get the serial decode option enabled, 28Mpts memory and battery. They also manufacture the DP10013 which is a differential probe for around $150.

author: CraftyAndy
author_rank: Newbie
timestamp: August 20, 2018, 10:14:13 pm
content: Quote from: TK on August 20, 2018, 10:08:57 pmI like the looks of that DFP10013 probe, thanks for the tip! I'll look into the TO1104 more as well, much appreciated!

author: fonograph
author_rank: Frequent Contributor
timestamp: August 21, 2018, 01:06:47 am
content: If you have 3k $ budget,stay away from anything Chinese no matter what anyone suggests to you.The way they handle bugs is simply outrageous and unacceptable.Get some Rohde & Schwarz RTB 2000 or Keysight 3000X.

author: TK
author_rank: Super Contributor
timestamp: August 21, 2018, 01:14:40 am
content: $3K budget including current and high voltage probes... I think R&S and Keysight are out of range...

author: Fungus
author_rank: Super Contributor
timestamp: August 21, 2018, 09:08:52 am
content: Ignore the people who only read the title and thought "He wants a $3K oscilloscope!".With those requirements you need an entry level oscilloscope and some very fancy probes.(ie. No real bandwidth requirements, just high voltage/current)That said: At those power levels a simpleshuntwill do for looking at the current and a simple (but enclosed) voltage divider will work for the voltage.For working with those shunts you'll need something that works well in the mV ranges (or put two or three shunts in series). Maybe something with 12-bit resolution so now we're full circle back to expensive oscilloscopes.

author: Andreas
author_rank: Super Contributor
timestamp: August 21, 2018, 09:41:15 am
content: Hmm the prices seem to have higher priority than the specs which are still not clear:- do you really want to spoil the accuracy of a normal current clamp (1%) by the gain error of a 8 bit scope (3%).- how many sample memory is necessary e.g. for measuring a complete run up phase of the motor including (parallel) CAN message sampling.- are pass/fail masks necessary for the production- is the scope only needed for viewing or is the measured data (complete or screen shots) to be stored on a PC.- is remote control for the scope needed (e.g. by remote desktop)- how often is the zoom function needed (and how easy can it be handled).with best regardsAndreas

author: Fungus
author_rank: Super Contributor
timestamp: August 21, 2018, 10:27:10 am
content: Quote from: Andreas on August 21, 2018, 09:41:15 amDo you really need to know the current of a 200A motor to 3 decimal places?You should probably be adding 50% (or more) to the power supply and wiring specifications, so 3% accuracy is plentyBuilding a shunt into the motor might be a good idea anyway, for on-site diagnosis, etc.Edit: If you want more decimal places it's probably better to buy more accurate shunt ($20) and add a $5 op-amp module to it rather then spend an extra $1000 on the oscilloscope. This setup will work on-site, too, when the maintenance guy connects up his Fluke and sets it to min-max mode.

author: mzzj
author_rank: Super Contributor
timestamp: August 21, 2018, 12:06:54 pm
content: Quote from: Fungus on August 21, 2018, 10:27:10 amOP wanted to measure current transients (20khz current clamp was also mentioned)Normal 60mV 200Amp shunt is borderline useless at 10khz because of the self-inductance. Coaxial shunt's have much better high frequency response but more tricky to mount and price/availability sucks.

author: Fungus
author_rank: Super Contributor
timestamp: August 21, 2018, 12:34:45 pm
content: Quote from: mzzj on August 21, 2018, 12:06:54 pmWon't it be background noise compared to the inductance of the motor?

author: CraftyAndy
author_rank: Newbie
timestamp: August 21, 2018, 03:24:27 pm
content: Thank you everyone for some good questions, I believe I've addressed most of them below.I'd prefer to stay away from a shunt to keep wiring easier (no need to add a shunt inline), but from a price stand point it may be worth me reconsidering this. I hadn't considered it initially so I will have to now.QuoteVery good point, I should have been more explicit in my title/OP. Thank you for pointing this out.QuoteI do want to measure transients, but I don't expect they will be in the 20khz range, rather that the clamp I'd initially looked at should be sufficient to view transients as its response is (relatively) quick.Quote from: Andreas on August 21, 2018, 09:41:15 amWould prefer to get above 8 bits if possible. The picoscope 4444 accomplishes that.Quote from: Andreas on August 21, 2018, 09:41:15 amHard to know how long of a sample is needed, longer is betterA few seconds should be sufficient.Quote from: Andreas on August 21, 2018, 09:41:15 amNo plans for this, although the fact the picoscope has it doesn't hurtQuote from: Andreas on August 21, 2018, 09:41:15 amWould like the ability to export to CSV or similar for post-processing in excelQuote from: Andreas on August 21, 2018, 09:41:15 amNo immediate needs or plans for thisQuote from: Andreas on August 21, 2018, 09:41:15 amZoom is important, I'm not sure if a knob or a mouse will be easier for me, but I'm comfortable with both.QuoteNo, to 1's place is fine in all honesty...

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 21, 2018, 05:40:14 pm
content: Quote from: CraftyAndy on August 21, 2018, 03:24:27 pmyou must have a very good reason for spending $1K+ on USB 14 bit scope, such as in audio-not-phoolery business try looking at THD, or a higher resolution FFT. probing 200A even down to mA resolution is not good enough reason, 14 bit aint going to cut it anyway, you need at least 18 bit. and there is a better way of doing that in $300 standalone (bench or handheld) scope. first you need to know what you are doing (which i suspect you dont), and then you can make a better list. why dont you just buy $300 8 bit scope (most recommended instead of something not recommended) and learn how to probe what you wanna see, or wiser ask in forum for that particular subject. a few members here are x-generation since DS1052E (upgrade to DS1054Z due to better performance) and never regret the advice from Mr Dave Jones, whose videos you need to hear from time to time.beside the $300 rigol/siglent/hantek whatever china brand recommended you are going to need current probe, since you mentioned DC, so you need hall effect type such asthisbut if you really hate china, you can get $900+thisused but then it only goes to a few Amp, iirc there is big clamp from Fluke (expect another $1K+++++) but they only do AC, and then soon you will realize what you probably are asking for a fortune on current probe alone. ymmv.

author: CraftyAndy
author_rank: Newbie
timestamp: August 21, 2018, 06:48:54 pm
content: Quote from: Mechatrommer on August 21, 2018, 05:40:14 pmHi there,Thank you for your input. I'm not sure why you feel I don't know what I'm doing, I feel that my responses to the questions thus far have been informed and addressing the point.The tektronix probe you linked below is the style I used at my last job. I have fairly extensive oscilloscope usage experience, but I've never had the pleasure (or pain) of picking one out and buying it. That part I'm very new to, and is why I've spent time researching it and asking questions about my proposed shopping cart.If you have any input on the proposed cart and its ability to accomplish what I've mentioned I'd appreciate the input.Thanks,

author: 2N3055
author_rank: Super Contributor
timestamp: August 21, 2018, 07:52:46 pm
content: For your stated requirements that Picoscope cart will serve you quite well.Picoscope is good equipment, and if you don't expect it to be full replacement for a scope with buttons and screen they are excellent.That scope, in addition to high res, has fully differential inputs.I have both Picoscope (not that model) and standard scope, and I use Pico quite often. No button-twiddling scope has 24" screen...It also have advanced math etc etc...

author: tautech
author_rank: Super Contributor
timestamp: August 21, 2018, 08:25:10 pm
content: All of what Andy wantscanbe bought quite cheaply in brands other than Pico excepting for their well priced current probe which TBH makes their package attractive.I did a bit of an exercise yesterday and put together a package from Siglent where by a long way their 3rd party current probes were the biggest value item in the package but none are scope powered like the Pico in this price bracket.To get it down a bit, a Dif probe like Pintek DP-25 and a Pintek current probe could pull $500 from the total price and then we'd get under the Pico cart price with a higher BW 100 MHz 4ch DSO.Two things that nag me about the Pico (and maybe someone knows better) are the apparently low voltage rated inputs and I couldn't find accuracy specs for their current probe.I enjoy brain teasers like this...........

author: 2N3055
author_rank: Super Contributor
timestamp: August 21, 2018, 09:02:32 pm
content: 12/14 bit scope with 256 MS memory, 4CH and fully differential inputs.....Advanced arbitrary math, 1M point FFT.....Yeah, gazillion of those around...This is scope custom made for exactly this type of work.Low voltage what?Input ranges (full scale) ±10 mV, ±20 mV, ±50 mV, ±100 mV, ±200 mV, ±500 mV,±1 V, ±2 V, ±5 V, ±10 V, ±20 V, ±50 V ±2.5 V, ±5 V, ±12.5 V, ±25 V, ±50 V, ±125 V, ±250 V, ±500 V, ±1000 VInput common mode range ±5 V on ±10 mV to ±500 mV ranges±50 V on ±1 V to ±50 V ranges ±125 V on ±2.5 V to ±12.5 V ranges±1000 V on ±25 V to ±1000 V rangesAs for current probe, you could or couldn't find specs?Accuracy (0 to 200/1500 A)±1% of reading ± 100 mA, ± 500 mAAccuracy (1500 to 1800 A) ±3% of readingAccuracy (1800 to 2000 A) ±6% of reading

author: tautech
author_rank: Super Contributor
timestamp: August 21, 2018, 09:08:42 pm
content: Quote from: 2N3055 on August 21, 2018, 09:02:32 pmScope input spec:±100 V DC + AC peak (any differential input to ground)±100 V DC + AC peak (between differential inputs)QuoteThanks, didn't find that.

author: mzzj
author_rank: Super Contributor
timestamp: August 21, 2018, 09:13:27 pm
content: Quote from: Fungus on August 21, 2018, 12:34:45 pmUmm..no.Electronics 101: Your AC current measurement results go haywire if the shunt impedance is 0.25 milliohms instead of assumed 0.1milliohm.It doesn't take much inductance even at "low" frequency like 10khz if the shunt resistance is very small (like high current shunts are)For example 0.3mOhm shunt resistor with 10nH series inductance has 10% error at around 2 khz.(and if you are measuring watts/power thing get 10 times worse because phase shift error starts to show at about 200hz with the aforementioned shunt values)(there is also another added error from skin depth )

author: 2N3055
author_rank: Super Contributor
timestamp: August 21, 2018, 09:17:45 pm
content: Quote from: tautech on August 21, 2018, 09:08:42 pmYes, you are right about that. They are not as robust in that regard. That is their weakness.Not a problem with high voltage probe (±1000 V DC + AC peak in that case), which is something you would use for it anyways...

author: tautech
author_rank: Super Contributor
timestamp: August 21, 2018, 09:26:38 pm
content: Quote from: 2N3055 on August 21, 2018, 09:17:45 pmWhich is not ideal when a 1:1 connection for greater sensitivity is required.SHS1000 isolated ch HH spec:CATII1000V and CATIII600V between two channels references，between channels reference and earth groundCATII600V and CATIII300V between channels reference and Multimeter input referenceCATII300V and CATIII150V input directCATII1000V and CATIII600V input with 10:1 probe

author: 2N3055
author_rank: Super Contributor
timestamp: August 21, 2018, 10:03:54 pm
content: Those isolated scopes are very useful. For other purposes. Very nice machines.If you need better detail, you have 12/14 Bit resolution. That is 16x/64x more vertical pixels. Which virtually enhances your vertical range that much times.So on a 8bit scope on 1V/div and 12bit 12V/div and 14bit 64V/div you have same vertical resolution.... It is fascinating how much more detail you can get...

author: nctnico
author_rank: Super Contributor
timestamp: August 22, 2018, 08:17:09 am
content: Quote from: tautech on August 21, 2018, 09:26:38 pmBut it has 200x attenuation and only 1MHz bandwidth IIRC so not very useful. Better get a differential probe. MicSig has a very good differential probe for a reasonable price. And then there is always the Pintek DP-25.

author: tautech
author_rank: Super Contributor
timestamp: August 22, 2018, 09:33:27 am
content: Quote from: nctnico on August 22, 2018, 08:17:09 am<Sigh.>You IIRC badly.Standard supplied SHS1k probes are 250MHz, 10x and 1kV CATII rated. Pt# PB925. They are special high insulation probes and a little bulkier than std probes.The SHS1k HH scopes are 60 or 100 MHz with 2Mpts memory.The SHS800 series have models from 60 to 200 MHz and use std scope probes.

author: nctnico
author_rank: Super Contributor
timestamp: August 22, 2018, 10:10:08 pm
content: Quote from: tautech on August 22, 2018, 09:33:27 amSince the topic moved to differential probes I was thinking about the isolation 'amplifier' box from Siglent and not a portable oscilloscope. My bad.

author: tautech
author_rank: Super Contributor
timestamp: August 22, 2018, 10:16:57 pm
content: Quote from: nctnico on August 22, 2018, 10:10:08 pmAh yes, the ISFEhttps://www.siglentamerica.com/accessory/isolated-channel-optional-accessories%EF%BC%88isfe%EF%BC%89/The Pintek DP-25 outperforms it.ISFE's only benefits are physical size, direct coupling to DSO inputs and powered from USB.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 26, 2018, 09:02:28 pm
content: Hi,IMHO your package should work if you dont mind the limited precision and frequency range (you have seen the datasheet) of your current probe.Current probes tend to be *noisy*, too. This can be a real nuisance in the low current ranges.It could make a lot of sense to measure smaller currents with a different probe.Standard 1:10 voltage probes should work, too.I would suggest that you make an extensive try before buy for your complete setup.

author: Rohde_TestWalker
author_rank: Newbie
timestamp: September 18, 2018, 05:15:11 pm
content: Hey CraftyAndy,There are a few other options to consider, like leasing or buying used. Is it for long-term use or a single project? Leasing is good for shorter term (and the leasing conpany take care of all the maintenance and calibration). If you opt for used equipment, you can get a good deal, but make sure you calibrate it before using.There's a third option: wait for a major player to have special deals. I'll email you off-line about a special deal coming up from a "well known vendor of high-quality equipment." I can let the broader forum know about it when it goes more public. Standby for a direct email...Good luck! And standby for that incoming email.Rohde_TestWalker