Crash course in unit conversions please!

Ask for and share advice on using the PicoScope kit to fix vehicles here.
Technician
TwoWaves
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Crash course in unit conversions please!

Post by Technician »

OK I'm new to the PicoScope and learning everyday, but I see many examples from more experienced professionals using volts in place of amps with reference to the vertical scales of the scope, so my question is this;

If I don't know how many mV or Volts equate to ma or amps how has the comparison been done!

I can't use P = V x I so what has been used in its place!

Thanks :?

speck
TwoWaves
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Re: Crash course in unit conversions please!

Post by speck »

I haven't seen many that use Volt instead of Amps, but this could help you.
Attachments
custom_probes.pdf
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Technician
TwoWaves
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Re: Crash course in unit conversions please!

Post by Technician »

thanks speck ill give that info a read through

speck
TwoWaves
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Re: Crash course in unit conversions please!

Post by speck »

Hi, forgot to tell you that you have the pico connected to your pc to create your own probes.

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TwoWaves
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Re: Crash course in unit conversions please!

Post by Technician »

Thanks Speck I'm reading through the custom probes guide taking it in. :)

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TwoWaves
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Re: Crash course in unit conversions please!

Post by Technician »

I don't know how true this statement is but I have just learned today from a uTube video that 'amps' on the vertical axis of PicoScope are actually volts!

Unless somebody believes differently I understand this to be true;

100 mV = 1 A
500 mV = 1/2 V = 5 A
1000 mV = 1 V = 10 A

volrem
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Re: Crash course in unit conversions please!

Post by volrem »

Oh boy. This proves to be a challenge but let's try.

Am I correct saying that you did get that from Frank Massey videos?


Your Picoscope will only measure voltage and therefore will only display voltage (in y-axis) against time (in x-axis).

Your Picoscope is unable to measure current, pressure and other non-voltage things directly.

To measure current you use for example current clamp (or current probe in some areas of world). Current doesn't flow to your scope but this current clamp measures current passing through and converts it to voltage. Same thing with pressure transducers. Pressure is measured and converted to voltage and this voltage can then be measured by your scope.

To make your life easier Picoscope software can convert this voltage back to current. And not really make current out of voltage but instead display it to you in easy readable way.

If you don't like using custom probes and let Pico do the maths for you rather than calculating yourself you can always stay in voltage mode. I prefer Pico to calculate for me.

If you use Pico current clamp TA018 (20A/60A) then current vs voltage output is: 1 mV/10 mA (100 mV = 1 A) for 20A range and 1 mV/100 mA (10 mV = 1 A) for 60A range.

So when measuring 18A in 20A range you get 1800mV in your Pico screen (when using standard voltage measurements and not selecting probe from menu). Same 18A in 60A range will produce 180mV.

When using 200A/2000A TA167 current clamp then outputs are 10 mV/A for 200A range and 1 mV/A for 2000A range. So 18A would output 180mV and 18mV respectively.

Every measurement device that converts measurement to voltage has conversion specifications written onto device or in user manual. To stay with voltage display in Pico you just have to know that information and do calculations in your head. I prefer using Pico to do that for me.

I maybe way off answering your question. Feel free to let me know when you did think about something else and show us a video that you got that information. I still feel that I didn't understand what you really meant.

Statement that
100 mV = 1 A
500 mV = 1/2 V = 5 A
1000 mV = 1 V = 10 A
is always true is not correct. But for some correct clamps it is like that.

And if you measure real voltage (not being output by current clamp) like car battery then this still remains still voltage and cannot be converted to current. You can measure voltage drop and calculate current/resistace and other things if you know needed parameters and how to do that but thatstoo high tech at the moment.

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TwoWaves
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Re: Crash course in unit conversions please!

Post by Technician »

Thanks Volrem for your time and effort there, the information is very much appreciated. I'll print a copy and keep on file for later use, the scope is very much a new learning curve for me.

The video was not Frank Massey, it was Scanner Danner scope basics part 1.

I think maybe the best way forwards for me here is to use the settings in the scope and just remember that the scope displaying amps is actually volts. I'm only confused when others using the scope display amps in volts mode and I wonder what the correct amps then actually are. Later I'll post an example pico file for you to look at.

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TwoWaves
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Re: Crash course in unit conversions please!

Post by Technician »

This is the closest example I can get to what I mean at the moment.
inj voltage current piezio peugeot 307.psdata
(416.11 KiB) Downloaded 480 times
If you read the vertical scales they are all in voltage, the red voltage I take to be the current and it reads 120 V, the injector voltage is 120 V also, The injectors switching on and off are around 8 amp and 4 amp I think without looking back. Unless I'm reading something wrong that red trace if current is high!

Sorry I might be reading this scope data incorrectly, the switching current on and off looks like 6 amp looking back on it, the voltage is initially 160 V dropping to 120 V, but am unsure what the red trace is! Is it the injector on time?

volrem
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Re: Crash course in unit conversions please!

Post by volrem »

Blue - Injector voltage negative side
Red - Injector voltage positive side
Green - Injector current
Yellow - Stays at 0V so probably not connected.


This file is great example of bad practice.

First there is no channel labels about what is measured or same info provided in notes.
No information about what current clamp was used on green channel or information about tool output. So you cannot convert voltage to amps if you don't have that information. Well actually you can but you don't know if it's 5,7 / 57a or any other result.

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