TA375

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tkelly
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TA375

Post by tkelly » Wed Nov 07, 2018 7:10 pm

Hello
I was wondering if the ta375 would be helpful with can or is it more so for flex-ray speeds.I have been using regular pico leads to test can signals and it seems to work fine.What i would like is to see is if there is a difference between can signals between regular leads and high bandwith leads.If anyone has comparison shots i would love to see the difference.

Thanks
Tom

Steve Smith
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Re: TA375

Post by Steve Smith » Fri Nov 09, 2018 1:56 pm

Hi Tom, thank you for the post and sorry for the late reply.

I think the best way to cover this is to present some example waveforms as you have suggested.

I will get to this on Monday and feedback ASAP.

Could I ask Tom when measuring these networks, would you normally wish to capture a single screen/buffer containing infinite detail to view/evaluate the structure of a single data packet or........

Capture a buffer full of data (E.g. 32 waveforms) allowing you to evaluate/decode multiple data packets/ messages

I guess the answer is both but if you have some desired settings for your scope for these networks just let me know and I will capture accordingly

Take care........Steve

tkelly
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Re: TA375

Post by tkelly » Sun Nov 11, 2018 11:53 am

Hi and thanks for responding.
I am more interested in looking at a full buffer of data.
My main interest is capturing and locating faults in network communication and would the ta375 supply more definition compared to standard leads.My main question is looking at the same can network with the 2 different leads would you see an obvious difference.I am new at network diagnostics and wonder if this will help me learn or would it be better to stick with the basic leads first.

Thanks Tom

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Autonerdz
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Re: TA375

Post by Autonerdz » Sun Nov 11, 2018 11:21 pm

Tom,

Your basic test leads are perfectly fine for CAN. I believe they have a 5MHz bandwidth so you would not need the higher bandwidth probe for CAN. You would for Flex Ray though.

Steve Smith
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Re: TA375

Post by Steve Smith » Tue Nov 13, 2018 10:21 pm

Hello and thank you for your patience on this one.
Please find below a comparison of the TA375 High Impendence probe https://www.picoauto.com/products/test- ... 00-mhz-bnc
against the standard Premium 3 M Test Leads included with our PicoScope kits (TA-125 - TA-128) https://www.picoauto.com/products/test- ... A125-TA128

Both leads were connected to a BMW F31 PT CAN network at 500 kbp/s and BMW F31 FlexRay network at 10 Mbp/s. The vehicle engine was running through all tests in order to subject the networks to their typical noisy environment.

All CAN measurements using the TA375 used the x1 attenuation mode, setting the test lead bandwidth to 10 MHz

CAN using standard Premium 3 M Test Leads (5 MHz Bandwidth)
TEST 1 CAN 200 MS-DIV.jpg
CAN STD LEAD
CAN using TA375 High Impendence probe set to x1 attenuation (10 MHz Bandwidth)
TEST 4 CAN TA375 200 MS DIV.jpg
CAN TA375
CAN using standard Premium 3 M Test Leads (5 MHz Bandwidth)
TEST 2 CAN 20 US DIV.jpg
CAN STD LEAD
CAN using TA375 High Impendence probe set to x1 attenuation (10 MHz Bandwidth)
TEST 5 CAN TA375 20 US DIV.jpg
CAN TA375
CAN using standard Premium 3 M Test Leads (5 MHz Bandwidth)
TEST 3  CAN  20 MS 32 BUFFER.jpg
CAN STD LEAD
CAN using TA375 High Impendence probe set to x1 attenuation (10 MHz Bandwidth)
TEST 6 CAN TA375 20 MS DIV 32 BUFFER.jpg
CAN TA375
Whilst there is no doubt the TA375 presents a superior reproduction of each CAN bit with minimal “ringing”, the standard Premium 3 M Test Leads perform exceptional well with sufficient resolution to identify anomalies and accurate decoding.

All FlexRay measurements made below using the TA375 utilise the x10 attenuation mode, setting the test lead bandwidth to 100 MHz

FlexRay using standard Premium 3 M Test Leads (5 MHz Bandwidth)
TEST 10 FLEXRAY 200 MS DIV.jpg
FLEXRAY STD LEAD
FlexRay using TA375 High Impendence probe set to x10 attenuation (100 MHz Bandwidth)
TEST 7  FLEX TA375 200 MS DIV 2.jpg
FLEXRAY TA375
FlexRay using standard Premium 3 M Test Leads (5 MHz Bandwidth)
TEST 11 FLEXRAY 5 US DIV.jpg
FLEXRAY STD LEAD
FlexRay using TA375 High Impendence probe set to x10 attenuation (100 MHz Bandwidth)
TEST 8 FLEX TA375 5 US  DIV.jpg
FLEXRAY TA375
FlexRay using standard Premium 3 M Test Leads (5 MHz Bandwidth)
TEST 12 FLEXRAY 20 MS 32 BUFFERS.jpg
FLEXRAY STD LEAD
FlexRay using TA375 High Impendence probe set to x10 attenuation (100 MHz Bandwidth)
TEST 12A FLEXRAY TA375 20 MS 32 BUFFERS DC.jpg
FLEXRAY TA375
Without doubt the bandwidth of the TA375 shines through for a true representation of high frequency FlexRay signals (Baud rate 10 Mbp/s)

The errors present within the FlexRay decode for both test leads is under review and I will feedback ASAP

Follow up 03/04/19

Regrding the FlexRay decode I mentioned how the decode feature for FlexRay was not successful. This was “Pilot Error” on my behalf as you are required to “invert” either the differential voltages (A-B) or the signal captured on Channel A (Channel B does not require inverting for a successful decode) This is a little confusing I know and I will dig deeper as to why.
FLEXRAY DECODE.png
FlexRay Decode
I hope this helps, take care……Steve

tkelly
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Re: TA375

Post by tkelly » Wed Nov 14, 2018 4:00 pm

I want to thank you for taking the time to put that together.I was having trouble picturing how much of a difference the higher bandwith probe would show.It seems that even can networks can benefit from using this probe.
Thanks
Tom

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Steve Michener
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Re: TA375

Post by Steve Michener » Wed Dec 19, 2018 3:38 am

Hi Steve Smith
Thanks for the sample traces of the CAN and FlexRay. I have a question about the Bandwidth of the scope and probes. You used a 4425 scope with a bandwidth of 20Mhz while using two channels which I assume resulted in only 10Mhz per channel. Is that correct?
The general rule is that the scope have a bandwidth 5x the fastest signal. FlexRay is stated at 10Mbp/s so that would require a 50Mhz scope. How did the trace look so good with such a low bandwidth scope?

Thanks much

Steve Smith
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Re: TA375

Post by Steve Smith » Fri Dec 21, 2018 2:56 pm

Hello Steve and thank you for the feedback, sorry for the late reply.

The Bandwidth of the 4425 PicoScope is only affected by the Bandwidth limit feature (Hardware filter) https://www.picoauto.com/library/training/filtering ,
the style of probe connected to the scope, and using +- 50 mV range (on this input range the bandwidth is 10 MHz)

The number of active channels does not affect bandwidth however it does affect sample rate!

The maximum sample rate is 400 MS/s for a single active channel and 200 MS/s for 2 active channels etc. Sample rate will also change relative to the number of samples requested and the time span across the screen.

We can see this in Test 8 at 5 us/div where the sample rate is 200 MS/s yet Test 12A at 20 ms/div we have 5 MS/s. With that said, the effect on the resolution is quite dramatic between these captures (Test 8 200 MS/s v Test 12A 5 MS/s)

FlexRay at 10 Mbps is a 5 MHz clock and so a 20 MHz scope is fine as you can sample much faster than this.

I hope this helps and please feedback for any clarification.

Take care…..Steve

victor2k
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Re: TA375

Post by victor2k » Sat Dec 22, 2018 6:53 am

Hello,
We can't use TA125-128 for CAN FD or FlexRay measurements.It has a huge capacity compared to MI007(I don't have TA375 ),from my measurements it's four-seven times higher(depending by the compensation capacitor).If the input capacity of CAN FD transceivers is 5-10pF,for FlexRay Bus differential input capacitance is 5 pF then using some probes with hundreds of pF is useless and can interfere with the captured signal.
Also for coaxial cables we have the capacitance(pF/ft or m) so a shorter cable has a small capacity:use the shorter cable what you have.
Here you will find an example about the impact of different capacitive load on the dominant bit-time(fig.5)
45a96f795e0786cf8430736cda9946f4.pdf
(2.14 MiB) Downloaded 43 times
According to the specs.the scope input have 24pF//1Mohm,also TA125 have 330-340 pF(measured value,not specified in datasheet) and MI007 only 58-102 pF(measured,specified in datasheet is 46 pF)without attenuation ,with x10 attenuation I can't measure.A twisted pair of wires will have 25-30pF/meter,so I use this for CAN measurements but the capacity will be more than 50 pF(scope+ 1m of cable).
The rising/falling time of the diferrential bus voltage of FlexRay transceiver is 6-18ns and the sampling interval must be 5 ns what is the limit of my 4425 using 2 channels with 20 ms/div:(
Best regards

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Steve Michener
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Re: TA375

Post by Steve Michener » Fri Dec 28, 2018 6:26 pm

Hi Steve Smith
Thanks for the clarification on Bandwidth. Not sure where I got my information from, have any of the older PICO scopes reduced the bandwidth when channels were added?

Would it be a true that no matter how fast the sample rate was, if the speed of the input signal is close to the bandwidth of the scope there will be significant loss of data?

I am curious how the flexRay clock is 5Mhz yet it can transmit at 10Mbp/s, but that is probably a discussion more suited for an multi page paper then this form. Even so, if the flexray signal can change at 10M times a second, scope recommendations, as I understand them, state the scope should be 5x the fastest signal. Even if the signal is changing at 5Mhz [which is confusing if it can communicate at 10Mbp/s] would require a 25MHz scope. It would seem the 5x recommendation is a touch over stated, or maybe in reality there is a loss of data? If the flexray was sampled with a 50Mhz scope and the TA375 probe, would it look any different?

Thanks

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