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nobbyclrk

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The picoscope and HIGH voltage
Jun 5^th, 2010 at 3:48am

Is the Picoscope and equipment able to handle the voltage inputs/outputs of the motor/generators on hybrid vehicles like the Prius? I have been told that the differential voltage across the motor can reach 800volts and upto 105amps (these were measured by the guy himself).
Also, is it likely I will see a loading effect on the attenuator? One of the scopes he used did show this loading.
And does the Picoscope have a seperate internal attenuator allowing it to handle the 100v inputs? (He assumed it did)
I'm not sure what benefits these measurements have, but, if needed, I would like to know if the pico is up to the job.

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Tom Roberts

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Re: The picoscope and HIGH voltage
Reply #1 - Jun 5^th, 2010 at 6:53am

We do not recommend that you connect to any hybrid HV circuits directly with PicoScope. Damage to the equipment and/or personal injury can result. We suggest the use of the TA057 CAT III differential isolation probe found at the bottom of this page:

http://www.autonerdz.com/miscellaneous.html

This is what our hybrid guys are using who wish to see stuff on the HV side.

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nobbyclrk

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Re: The picoscope and HIGH voltage
Reply #2 - Jun 6^th, 2010 at 12:24am

Thanks Tom. At first I thought I got a wierd answer, but the I realized I had a case of foot in mouth and asked the wrong question. But from your answer, worked it out.

I had just come back from a couple of coarses on common rail diesel followed up on one which covered hybrids. We were going through doing lots of offset and differential measurements while using different types of scopes including the normal type scope, a differential and one that could except direct input of high voltages. And somehow my brain decided I had a differential scope Shocked

. That may be CATIII compliant.( It's been a long week. )

The reason I asked about the attenuators I didn't realise one of the scope's we used allowed direct high inputs and that any scope using attenuators will squew the voltages if the are high enough and fast switching. Is that right? Trying to sort out tutor scope bias from real life. It does get confusing Huh

But I did learn more about using differential measurements as another tool/technique in diagnostics. It is good to know what the equipment is capable of even though it'll be a while before I feel confident of taking any hybrid HV measurements. And it's interesting to have a bit of an understanding on how a system works.

Now I'll go off and try and get my foot out my mouth. Wink

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Tom Roberts

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Re: The picoscope and HIGH voltage
Reply #3 - Jun 6^th, 2010 at 9:56am

Hi Andy,

Sorry if I misunderstood the question.

Quote:

any scope using attenuators will squew the voltages if the are high enough and fast switching. Is that right?

No, it depends on the attenuator. The Pico attenuators do not distort the signal if the signal does not approach the rated bandwidth of 10 MHz.

Additional safety comments from the Pico attenuator page:

"Fuel injector and primary ignition signals contain short duration high voltage spikes “inductive kicks”. We therefore recommend the use of two ground connections between the oscilloscope and the vehicle under test. One ground connection is made using the measurement test lead. A second ground lead should be connected between one of the BNC connectors on the oscilloscope and a secure ground point on the vehicle such as the negative terminal of the battery. Misconfiguration and/or failure to follow these warnings may cause damage to the product and/or computer and could cause injury to yourself or others."

http://www.picoauto.com/attenuator.html

Quote:

But I did learn more about using differential measurements as another tool/technique in diagnostics.

I don't get into operational technique or strategy in the public forums. We can take this to the Picogroup area if you want more information. But briefly:

You can perform direct differential measurements, if only using one channel, but not if sampling higher voltage spikes using the attenuator. (see above). However, there is no real need to do this because we can utilize the channel math functions to calculate differentials while using a safer and more versatile hook up.

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nobbyclrk

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Re: The picoscope and HIGH voltage
Reply #4 - Jun 7^th, 2010 at 2:31am

Thanks again Tom

Thats what I was after. I enjoy the learning in these coarses. But as I said, sorting out the real truth of scope capabilities from the chaff of underhand selling technique can be frustrating at times Huh

. And funny at other times Grin

. The usual trick is software manipulation to make one scope look better or worse than the other. But I kind of now know to take the "my scope is the best because...." with a pinch of salt and do the research myself. The Nerd 1 cd got me to look more closely at the specs and wording and read between the lines. Unfortunatly alot of people do get caught out by part truths. I definatly have had no regrets about buying the pico. Good stuff and good fun. Anyway enough said.

Good point on the attenuators. I'll keep that in mind Wink

I never would of thought about using the maths channel for this type of application. A handy trick to remember. The single channel use had crossed my mind. That and your point on the attenuators has brought up another couple of questions. But I'll ask over in the picogroup area once I figure out how to say what I want to know. Cheers again!
Andy

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CW Freshman Member Picogroup Offline Posts: 38 Denver Colorado USA Gender:	Re: The picoscope and HIGH voltage Reply #5 - Feb 18^th, 2015 at 10:17pm Wait, so have I been connecting my Pico wrong all this time? When looking at injectors, I use the 20:1 attenuator, and connect a test lead (say CHA) to the injector and the ground lead of the same BNC cable (CHA) to ground. Pico recommends using an additional ground?
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Tom Roberts Autonerdz Administrator Picogroup Offline Autonerdz Founder Posts: 8,595 Olympia Washington USA Gender:	Re: The picoscope and HIGH voltage Reply #6 - Feb 19^th, 2015 at 10:02am CW wrote on Feb 18^th, 2015 at 10:17pm: Wait, so have I been connecting my Pico wrong all this time? No. Your fine. Unless you are using a 4425, all the grounds are common. Only one channel needs to be grounded and the preferred point for that is bat neg.
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CW

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Re: The picoscope and HIGH voltage
Reply #7 - Feb 19^th, 2015 at 11:34am

Tom Roberts wrote on Feb 19^th, 2015 at 10:02am:

No. Your fine. Unless you are using a 4425, all the grounds are common. Only one channel needs to be grounded and the preferred point for that is bat neg.

Got ya! I knew all the grounds were in common for the 4423, which is why I thought it was recommended to only connect 1 ground, regardless of how many leads/channels used. I did not realize the 4425 uses separate grounds for each channel. That would make sense why Pico recommends connecting each channel to a ground. Has this been discussed before? As to why they made that change?

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Re: The picoscope and HIGH voltage
Reply #8 - Feb 19^th, 2015 at 1:18pm

CW wrote on Feb 19^th, 2015 at 11:34am:

I did not realize the 4425 uses separate grounds for each channel

New design. Pico calls it floating inputs. Each channel must have a ground reference and the grounds for the channels can have up to a 30 volts difference.

These 4425 scopes have been discussed in the public areas here:

http://www.autonerdz.com/cgi/yabb2/YaBB.pl?num=1410881365

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haydenw

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Re: The picoscope and HIGH voltage
Reply #9 - May 2^nd, 2015 at 1:06pm

Tom Roberts wrote on Jun 6^th, 2010 at 9:56am:

Hi Andy,

No, it depends on the attenuator. The Pico attenuators do not distort the signal if the signal does not approach the rated bandwidth of 10 MHz.

Additional safety comments from the Pico attenuator page:

"Fuel injector and primary ignition signals contain short duration high voltage spikes “inductive kicks”. We therefore recommend the use of two ground connections between the oscilloscope and the vehicle under test. One ground connection is made using the measurement test lead. A second ground lead should be connected between one of the BNC connectors on the oscilloscope and a secure ground point on the vehicle such as the negative terminal of the battery. Misconfiguration and/or failure to follow these warnings may cause damage to the product and/or computer and could cause injury to yourself or others."

http://www.picoauto.com/attenuator.html

So is this just the case with the 4425 and you are only using one channel? because of the floating grounds, say Channel A on a primary coil circuit with positive lead from bnc on the trigger side and the negative lead to battery earth then they would like Channel B or C or D earth to go to battery earth also? Or is it just if you have the leads from channel A BNC differentially across the coil say positive lead on coil positive and channel A earth to coil negative then u need a second channel earth to go to battery ground?

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Re: The picoscope and HIGH voltage
Reply #10 - May 2^nd, 2015 at 5:47pm

haydenw wrote on May 2^nd, 2015 at 1:06pm:

Or is it just if you have the leads from channel A BNC differentially across the coil say positive lead on coil positive and channel A earth to coil negative then u need a second channel earth to go to battery ground?

You would never want to hook up a scope that way. You are exposing the ground to 400+ V kicks. This is way over the 30V limit for the 4425. Plus there is no reason to hook up this way. It would provide no useful information over hooking up properly.

haydenw wrote on May 2^nd, 2015 at 1:06pm:

Channel A on a primary coil circuit with positive lead from bnc on the trigger side and the negative lead to battery earth then they would like Channel B or C or D earth to go to battery earth also?

That would be proper hook up for A. The other channel grounds could also be on bat neg. Or, in the case of a 4425, be located elsewhere, if desired, as long as the ground difference is less than 30V between channel grounds. Using a 4425, all channel grounds must be attached somewhere. When using a 4423, only one channel ground is needed since all channel grounds are common.

If you would like do discuss this in more detail, please make a post in the Picogroup area boards.

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haydenw

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Re: The picoscope and HIGH voltage
Reply #11 - May 2^nd, 2015 at 9:33pm

Tom Roberts wrote on May 2^nd, 2015 at 5:47pm:

haydenw wrote on May 2^nd, 2015 at 1:06pm:

Or is it just if you have the leads from channel A BNC differentially across the coil say positive lead on coil positive and channel A earth to coil negative then u need a second channel earth to go to battery ground?

You would never want to hook up a scope that way. You are exposing the ground to 400+ V kicks. This is way over the 30V limit for the 4425. Plus there is no reason to hook up this way. It would provide no useful information over hooking up properly.

haydenw wrote on May 2^nd, 2015 at 1:06pm:

Channel A on a primary coil circuit with positive lead from bnc on the trigger side and the negative lead to battery earth then they would like Channel B or C or D earth to go to battery earth also?

That would be proper hook up for A. The other channel grounds could also be on bat neg. Or, in the case of a 4425, be located elsewhere, if desired, as long as the ground difference is less than 30V between channel grounds. Using a 4425, all channel grounds must be attached somewhere. When using a 4423, only one channel ground is needed since all channel grounds are common.

If you would like do discuss this in more detail, please make a post in the Picogroup area boards.

Ok thanks tom

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Tom Roberts Autonerdz Administrator Picogroup Offline Autonerdz Founder Posts: 8,595 Olympia Washington USA Gender:	Re: The picoscope and HIGH voltage Reply #12 - May 3^rd, 2015 at 8:34am You're welcome. Hope that made sense. Basically, when using the 4425, I would reserve placing a channel ground on anything but bat neg unless you understand the circuit and what you are trying to accomplish.
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