Please recommend oscilloscope for robotics research

Please recommend oscilloscope for robotics research
Posted by eeguy on 02 Aug, 2016 23:21
Hello, I am considering to purchase an oscilloscope for robotics research at graduate school level. Having the ability to record the data during the experiments is nice. Good to have four channels. Any good recommendation appreciated. Thanks.

#1 Reply
Posted by ebclr on 02 Aug, 2016 23:37
Case you have a deep pocket

http://www.keysight.com/en/pdx-x201842-pn-DSOX3014A/oscilloscope-100-mhz-4-channels?cc=US&lc=eng

Case not

https://www.adafruit.com/product/2145

#2 Reply
Posted by tautech on 03 Aug, 2016 00:17
Quote from: eeguy on 02 Aug, 2016 23:21
Hello, I am considering to purchase an oscilloscope for robotics research at graduate school level. Having the ability to record the data during the experiments is nice. Good to have four channels. Any good recommendation appreciated. Thanks.
Welcome to the forum.

Yep, 4 channels are nice IF you need any HV capability for all 4, seldom you will in my experience.
A 2 channel MSO is then a viable option and offers more total channel #'s too.

In this case I would suggest a SDS1000X+ series with the MSO/LA option.
http://www.siglentamerica.com/pdxx.aspx?id=4688&T=2&tid=1

Or it's big brother, the SDS2000X series, these are available in 2 or 4 channels and MSO/LA option.
http://www.siglentamerica.com/pdxx.aspx?id=1488&T=2&tid=1

#3 Reply
Posted by Hydrawerk on 03 Aug, 2016 00:19
Consider some from Keysight DSOX2000A series. But only you decide what you really need. Yes, this scope was introduced in 2011.

#4 Reply
Posted by PartialDischarge on 03 Aug, 2016 02:22
definitively dont get an usb scope. Cost and spec wise, either get a rigol or a siglent which are 'expandable' in memory and will give you more features than you need
The forum has lots on threads about first buy scopes like these.

#5 Reply
Posted by Hydrawerk on 03 Aug, 2016 02:30
Quote from: blueskull on 03 Aug, 2016 01:29
[
2Mpts memory without segmentation is a big no go, unless you pay extra money for MEMUP and SGM options.
Mine has all options (they sell an all-in-one option pack), and even that, sometimes memory is just not enough.
Then you must consider GW Instek GDS-2000E. http://www.gwinstek.com/en-US/products/Oscilloscopes/Digital_Storage_Oscilloscopes/GDS-2000E

#6 Reply
Posted by rstofer on 03 Aug, 2016 02:31
There are a number of threads here about the Rigol DS1054Z 4 channel scope (and you do want 4 channels). I sure like mine.

#7 Reply
Posted by nctnico on 03 Aug, 2016 02:41
I'd go for a 4 channel scope and a simple (USB) logic analyser for hunting digital problems. I have an MSO on my bench but so far I have not used it. 4 channels gets me around and for real digital problems I pull out my logic analyser.

#8 Reply
Posted by rstofer on 03 Aug, 2016 04:56
Dave has done a few videos of the DS1054Z Here is he summary:

You can search YouTube for the others.

#9 Reply
Posted by lem_ix on 03 Aug, 2016 08:56
4 channels is always nice and decoding, preferably with canbus. I'd go with the instek 2000e(good value) but anything along those lines would do. Personally pretty happy with my R&S/Hameg hmo.

#10 Reply
Posted by eeguy on 03 Aug, 2016 15:46
Thanks.

I watched the video about the DS1054Z. The guy mentioned that the vertical scale of all four channels have to be the same. I guess it would be better if they could be set independently.

A potential use of the scope is to measure and record the power consumption of the motors during the experiments. For this application, should I use an oscilloscope or some other equipment?

#11 Reply
Posted by pascal_sweden on 03 Aug, 2016 15:52
You can set the vertical scale individually for each channel, but you have to use the same knob for it.
So that means that you have to select the active channel first, before you use the knob.

#12 Reply
Posted by eeguy on 03 Aug, 2016 21:11
Quote from: pascal_sweden on 03 Aug, 2016 15:52
You can set the vertical scale individually for each channel, but you have to use the same knob for it.
So that means that you have to select the active channel first, before you use the knob.

Thanks. Can this scope change the vertical and horizontal scales of each channel automatically?

#13 Reply
Posted by tautech on 03 Aug, 2016 21:17
Quote from: eeguy on 03 Aug, 2016 21:11
Quote from: pascal_sweden on 03 Aug, 2016 15:52
You can set the vertical scale individually for each channel, but you have to use the same knob for it.
So that means that you have to select the active channel first, before you use the knob.

Thanks. Can this scope change the vertical and horizontal scales of each channel automatically?
All DSO's have "AutoSet", a button that configures the scope based on the signal input. Primarily it's used by scope newbies as it often resets a scope to what IT thinks is best, not the user.
Auto Set is the only auto change of vertical and horizontal settings.
It can sometimes be useful however most experienced users prefer to "drive" their scopes.

#14 Reply
Posted by TAMHAN on 03 Aug, 2016 22:40
Quote from: tautech on 03 Aug, 2016 21:17
Quote from: eeguy on 03 Aug, 2016 21:11
Quote from: pascal_sweden on 03 Aug, 2016 15:52
You can set the vertical scale individually for each channel, but you have to use the same knob for it.
So that means that you have to select the active channel first, before you use the knob.

Thanks. Can this scope change the vertical and horizontal scales of each channel automatically?
All DSO's have "AutoSet", a button that configures the scope based on the signal input. Primarily it's used by scope newbies as it often resets a scope to what IT thinks is best, not the user.
Auto Set is the only auto change of vertical and horizontal settings.
It can sometimes be useful however most experienced users prefer to "drive" their scopes.

On the risk of sounding a lot like Wuerstchenhund now. I made quite odd experiences with my LC9300 series, which also deploys advanced triggers via AutoSet sometimes if it feels the need.

But yes, that would also be a recommendation for an LC9300 or one of the successors with DPO-like capabilities. I _really_ like their automatic analytics, which determine all kinds of parameters on the go. Plus, they are quite cheap on Ebay...and if you get the hard drive option, you get unlimited storage.

(Be aware that most of the FDD drives are toast, however)

#15 Reply
Posted by saturation on 04 Aug, 2016 00:10
You can use a wattmeter but the scope will allow you to view instantaneous values. This is most helpful in determining which actions consume more power.

E.g.

Place VDC across the motor on say CH1, a small value dropping resistor in series with its power line or a sensitive [ and expensive] DC current probe set on CH2. For dropping resistors you can convert CH2 to current if you can apply math function to the output, say CH2= CH2/R, were R is a constant in ohms to read output as amperes. You can then set CH3 = CH1x CH2 for instantaneous watts.

For total power integrate CH3 say set CH4= INTG(CH3).

Quote from: eeguy on 03 Aug, 2016 15:46
Thanks.

I watched the video about the DS1054Z. The guy mentioned that the vertical scale of all four channels have to be the same. I guess it would be better if they could be set independently.

A potential use of the scope is to measure and record the power consumption of the motors during the experiments. For this application, should I use an oscilloscope or some other equipment?

#16 Reply
Posted by eeguy on 04 Aug, 2016 01:14
Quote from: saturation on 04 Aug, 2016 00:10
You can use a wattmeter but the scope will allow you to view instantaneous values. This is most helpful in determining which actions consume more power.

E.g.

Place VDC across the motor on say CH1, a small value dropping resistor in series with its power line or a sensitive [ and expensive] DC current probe set on CH2. For dropping resistors you can convert CH2 to current if you can apply math function to the output, say CH2= CH2/R, were R is a constant in ohms to read output as amperes. You can then set CH3 = CH1x CH2 for instantaneous watts.

For total power integrate CH3 say set CH4= INTG(CH3).

Quote from: eeguy on 03 Aug, 2016 15:46
Thanks.

I watched the video about the DS1054Z. The guy mentioned that the vertical scale of all four channels have to be the same. I guess it would be better if they could be set independently.

A potential use of the scope is to measure and record the power consumption of the motors during the experiments. For this application, should I use an oscilloscope or some other equipment?

That is great! What suggestion do you have in the following two cases:

1. Measure and record the power consumption of the entire robot which consists of more than one motor.
2. Measure and record the power consumption of several motors of the robot at the same time.

#17 Reply
Posted by Jay_Diddy_B on 04 Aug, 2016 01:41
Hi,

To the OP you might want something that can do I2C and SPI decoding. You probably have I2C and SPI devices on the robot.

Regards,
Jay_Diddy_B

#18 Reply
Posted by saturation on 04 Aug, 2016 14:33
To measure the power consumption in toto, put a DC wattmeter in the V+ of the robot battery. This will give total power consumption. You can buy wattmeters anywhere, there are often sold in the RC hobby market; logging, non-logging, low power, very lower power, miniature etc.,

To measure power of each limb you put a wattmeter on V+ of the limbs.

Note, your choice of devices matter, DSO are only accurate to about 1-3% and DMM are far better but they do not show instantaneous power well. Also if you are using very low power, DC wattmeters, DSO and DMM have limits. Low low power power applications require low-load wattmeters that use hall effect transducers, which raise the cost of the device.

Be careful on your choice of DSO, e.g. the eevblog 'popular' Rigol 1054Z has reported bugs in its voltage readouts, and so far it may have others yet unreported. Any measurement bugs will give calculation errors even if the calculation algorithm is correct, and the waveforms appear be fine. So, buyer beware.

Enjoy.

Quote from: eeguy on 04 Aug, 2016 01:14

That is great! What suggestion do you have in the following two cases:

1. Measure and record the power consumption of the entire robot which consists of more than one motor.
2. Measure and record the power consumption of several motors of the robot at the same time.

#19 Reply
Posted by rstofer on 04 Aug, 2016 15:24
As stated, yes, the vertical V/div can be individually set. You briefly push the channel button to select the channel and then turn the knob. The scale will be shown at the bottom of the screen.

No, you can't set the time/div individually. Why would you want to? Normally, we use multi-channel scopes to view the relationship between signals and that implies the same time base.

You do power measurement by installing a shunt resistor on the + lead of the power source (battery, I assume) and then using a high side sense amplifier IC to measure the voltage drop. This results in an analog output voltage proportional to current. Another op amp will be used to scale the voltage (could use resistors) and the two signals will be sent to a uC ADC inputs where the numbers will be crunched. Pretty easy!

http://www.linear.com/products/Current_Sense_Amplifiers

Industrial shunt resistors are set to drop 50 mV at full scale, whatever it is. 1A, 100A, 1000A, they all drop 50 mV at full scale.

Decoding: So, the basic DS1054Z doesn't include decoding or the optional 100 MHz bandwidth and you have to dance with hacking the scope to get them (actually, they come with the scope with a time limit). This process is well understood. For the first time yesterday, I went live with decoding SPI with a 1 MHz clock rate. I am working with a chip that needs a LOT of SPI signaling http://www.mouser.com/ProductDetail/WIZnet/W5500 I think the scope will earn its keep before this project is over. There are limitations to the decoding because the scope only decodes what it displays, it doesn't look through the buffer. That's ok, once I get the basic transfer functions written, the rest is just details and they can be debugged in the uC using my favorite tool: printf();

#20 Reply
Posted by Assafl on 05 Aug, 2016 08:41
Not a scope - but has two channels logging DMM (at 8k sample rate) is the Mooshimeter.

As far as the story goes it was developed by engineers working on real robots (the dangerous full sized ones) so they designed it to be inexpensive, high A/D resolution, can be tie-wrap tied to a robot arm, has two channels and can be read remotely via Bluetooth.

The software and firmware still have some issues, but the developer is working hard to resolve most of them. It is becoming a rather useful device for remote monitoring and logging...

https://moosh.im/

#21 Reply
Posted by eeguy on 30 Aug, 2016 12:14
I am concerned about some of the issues mentioned in the video:

Have those issues been fixed?

#22 Reply
Posted by Fungus on 30 Aug, 2016 13:39
Quote from: eeguy on 30 Aug, 2016 12:14
Have those issues been fixed?

Ummm.... some of those aren't even 'issues'. It's mostly just a Rigol-bash by somebody who didn't bother to learn to use his 'scope.

eg. The thing about "channel buttons not working"

That's totally by design. The first press is to set the active channel if it's not already active (which you can see by a huge marker on screen). He says "button didn't work" but yes it did - you can see the marker change at the bottom of the screen. The second press will then turn the channel off. This is common to many (all?) oscilloscopes which don't have a separate set of controls for each channel, not just Rigol. He needs to either learn to use his 'scope or pay for the separate controls.

The fan? Yes, some forum members have replaced the fan for a quieter one.

The vertical movement? Yes, it looks bad if you savagely yank the knob around in a Rigol-bashing video. In real life:
a) There's a little marker at the side of the screen which adjusts faster than the trace. Use it.
b) You'll quickly get the 'feel' of the knob and learn to do it.
It's not ideal, some forum members have replaced the rotary encoder knob with a fatter one (this helps a lot). Some have even replaced the encoder with a clicky one. It doesn't make it unusable.

Could it be improved? Yes. Who knows what goodies the next firmware will bring?

If you're hopelessly ham-fisted or just want something a bit more 'refined' you can go for a different brand but you'll lose out badly in terms of technical specs (bandwidth, channels, memory size, serial decoders, etc).

The next real step up from a hacked DS1054Z in terms of spec. and niceness will cost you $1200+. Your call.

#23 Reply
Posted by rstofer on 30 Aug, 2016 14:22
Quote from: eeguy on 30 Aug, 2016 12:14
I am concerned about some of the issues mentioned in the video:

Have those issues been fixed?

Everything he mentioned, with the possible exception of the scope probes, is exactly correct. These human interface issues are exactly the kind of things that should lead you to buying something else. There are many other choices that are much better behaved. Perhaps one of the GW Instek models - they are known to be perfect.

Oh, wait! I bought the DS1054Z and the first thing I did was hack the unit to get 100 MHz bandwidth and keep the decoders. Next, I replaced the rotary selector switch with one having a detent mechanism. I have the replacement fan but I haven't found the noise to be compelling enough to open the unit up again. Yes, the UI is slow under some conditions; conditions I just don't run across very often. Or, if I do, I just deal and move on.

Channel selection works exactly the way it is described in the video. And it is the ONLY way it can work if the scope doesn't have separate controls for each channel (some do). Before you can adjust a channel, you have to select the channel. Seems pretty right to me!

Trace colors: Yellow, cyan, purple and blue. Yes, the purple and blue are 'similar'. But it's a whole lot better than using red for which a high percentage of the adult male population have a vision defect. Red is a horrible color to use.

Are you going to get a multi-thousand dollar scope for $400? Probably not! But if those issues are a concern, you would be better off buying a higher dollar scope. Clearly, the GW Instek will be much better - it kind of makes you wonder why the video author bought the Rigol.

#24 Reply
Posted by Assafl on 01 Sep, 2016 07:14
Quote from: rstofer on 30 Aug, 2016 14:22
Are you going to get a multi-thousand dollar scope for $400? Probably not! But if those issues are a concern, you would be better off buying a higher dollar scope. Clearly, the GW Instek will be much better - it kind of makes you wonder why the video author bought the Rigol.

The reason he seems to use it (all the time) is that with a single channel enabled (at 1GHz sample rate) he uses the DS1054Z to measure 400MHz signals with it. Attenuated quite a bit by the input filtering for sure - but still.

He also seemed to admit in later posts he was annoyed and ranted... But he uses the scope.

A funny aspect of these types of rants and criticisms is that they result in selection/observation type biases. I never had any issues with the selection knob until I read all those who couldn't click straight. Guess what - suddenly it became a problem.... There is a psychological aspect to oscilloscopes especially on the low end where users can't afford shrinks.