| Electronics > Beginners |
| Should I float a scope on a car |
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| tggzzz:
--- Quote from: Seamus16 on August 04, 2018, 10:12:28 am ---Thanks to all who have replied and the warnings are well noted. I suppose to satisfy yourself that you are in a safe environment would be to connect a multimeter between the scope chassis and the car earth. --- End quote --- Until something happens after you've measured that voltage. The circuit changes, or misplaced probe, etc etc. These problems aren't new, and companies have developed products to address the issues safely. Use the proper type of probe for the problem; see some references in https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/ There are, I believe, scopes specifically designed for automotive market, but I know nothing about them. |
| Brutte:
I did the single ended measurement on my car yesterday. The scope was properly earth grounded and the car was floating on its tyres. Then I connected the probe's shield to +12V battery connection making a car chasis float at around -12V below ground. No issues, measurement done (starting current). No smoke escaped. Although I must admit that I stripped all other shielded crocodile clips from other probes because in case one of those touched the chasis then most likely :-BROKE |
| Seamus16:
--- Quote from: Brutte on August 04, 2018, 10:36:20 am ---I did the single ended measurement on my car yesterday. The scope was properly earth grounded and the car was floating on its tyres. Then I connected the probe's shield to +12V battery connection making a car chasis float at around -12V below ground. No issues, measurement done (starting current). No smoke escaped. Although I must admit that I stripped all other shielded crocodile clips from other probes because in case one of those touched the chasis then most likely :-BROKE --- End quote --- I think a point should be added that both feet should be inside the car. I have habit of sitting in it with my feet on the ground. |
| Seamus16:
--- Quote from: tggzzz on August 04, 2018, 10:33:38 am --- --- Quote from: Seamus16 on August 04, 2018, 10:12:28 am ---Thanks to all who have replied and the warnings are well noted. I suppose to satisfy yourself that you are in a safe environment would be to connect a multimeter between the scope chassis and the car earth. --- End quote --- There are, I believe, scopes specifically designed for automotive market, but I know nothing about them. --- End quote --- That is correct and have several interfaces but none of them are managing to connect, hence I want to check the K Line to see if there is a signal on the line, but it is only giving a basic voltage of 10v which I think implies there is a problem existing somewhere. Thanks anyway I can now forget about any 240v issues and continue scratching my head https://www.eevblog.com/forum/Smileys/default/smiley.gif |
| Brutte:
--- Quote from: Seamus16 on August 04, 2018, 12:16:47 pm ---I think a point should be added that both feet should be inside the car. I have habit of sitting in it with my feet on the ground. --- End quote --- Why is that so? The chasis is just -12V (below earth gnd) so no significant currents expected to flow even when you keep one leg outside of the car. It is like touching a battery ( + ) terminal while standing on the ground. It is safe and as probe shield has very low impedance - that touching won't jam the measurements. Although making differential measurement is safer.. The starter is wired through copper wire directly to battery ( + ) so it is easy to measure current that way by clipping scope on both ends of that wire. Such measurement is impossible with negative wire as there are several paths of negative current. I would not recommend sensing K-line with serial2USB adapter tied to laptop that is powered from cigarette lighter socket. Been there, done that - it won't work. The laptop's GND jumps like crazy w.r.t. car's GND as laptop draws significant currents. |
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