Breakout Lead Risks?

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Breakout Lead Risks?

Postby Trent » Fri Jun 16, 2017 3:54 am

The description for breakout leads warns that incorrect connections could "short" my Picoscope and cause damage. It's easy for me to understand how a PCM could be fried. Please help me understand how my scope is at risk by shorting. I think I'm missing something here.

Thanks, Trent
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Re: Breakout Lead Risks?

Postby liviu2004 » Fri Jun 16, 2017 9:14 pm

With these type of connections, there is always a risk to put + on BNC ground channel A and a - on the other BNC ground on channel B, and if the scope has common connection internally between bnc grounds, there you have it, short circuit.

The latest automotive scope has isolated bnc connectors so risk is lower.
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Re: Breakout Lead Risks?

Postby ben.martins » Mon Jun 19, 2017 10:40 am

Hello and thank you for the post. Please accept my apologise for not answering this sooner.

I think it is essential here to establish the Automotive PicoScope you are using as their architecture differs somewhat depending on model. Given the close proximity of terminals within harness connectors there is always a chance of a power supply being connected to the BNC shell of your scope if you were intending to reference your signal to the ground of the sensor you are breaking into?

I know from experience how easy it is to get this wrong and would always advise every signal is referenced to chassis ground unless you are using the current 4225 or 4425 model. These scopes can be referenced to voltage + - 30 V from chassis ground. See the following link: https://www.picoauto.com/library/traini ... ing-inputs.

Either way, assuming you are using any of the Automotive PicoScope and you accidentally connect one BNC shell to +12 V when other BNC shells are connected to chassis ground, not a problem! The automotive scopes are protected internally from such events and will “trip out” the short circuit until it is removed where the scope will return to normal operation. The real concern has to be for damage to the components you are testing or the control module (e.g. PCM) responsible for their operation.

Whilst I have waffled on here about ground reference and short circuits, let’s not forget the maximum input voltage of your scope that is specified on your scope casing. The Automotive scopes are exceptionally robust when it comes to voltage spikes but if you are in any doubt about the voltage level of your input signal, use an attenuator to stay on the safe side.

To summarise here, Pico Automotive Scopes are designed for automotive use and include additional protection above and beyond that of Non-Auto Scopes.

Hopefully this helps to put your mind at ease when using PicoScope but if you have any further questions please don't hesitate to get in touch.

Kind Regards

Ben (with much thanks from Steve Smith!!)
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