Hello from a John Deere mechanic

[mechanichayfarmer]

My name is Aaron. I am a mobile mechanic who works for John Deere AG. I live in Michigan, USA. I work on all types of equipment but most of my time is spent on off road equipment. I have several manufactures of scopes that I use. This is my first pico. I have used scopes for several years and now am trying learn how to use a waveform generator and a scope to test controllers.

[ben.martins]

Hi Aaron,

Great to see more ag technicians looking to see how a PicoScope can help with their diagnosis.

Out of interest which Pico did you go for?

The forum is packed with information. Given the types of machinery you find yourself working on I would suggest checking out the HD and OH section - forum483.html.

We're all here to help and assist and look forward to seeing some interesting applications for scope in your industry.

Kind regards

Ben

[David Sinclair]

Hi i have been using a pico 4425 within my automotive workshop for many years now and its a brilliant tool for me, i am constantly using & training with it to keep my technical brain working..
I am actually looking for an answer from a Steve Smith tutorial recently on the Data log video. The tutorial from Steve was brilliant as i actually seem to get lots of parasitic vehicle drains from my customers as well as other garages. I made the 100 watt resistor with the 0.1 ohm and i have used a good 10 times since the recent video...
My question is when i connect up the unit ready to connect it already shows about 15 mA before connection and i am unsure if there is a way that i can zero this ? That said i am today carrying out the test on a 2010 Toyota IQ and yet after the car has gone to sleep i am only showing between 17-21 mA and i find it hard to believe that it is only using 5mA as a draw, so basically do you think the scope is zeroing upon connection ?????
I hope i have made sense and that somebody has the answer, ideally if Steve Smith reads this...
Many thanks for reading this...
David...

[ben.martins]

Hi David,

I know Steve will be in touch as well as we both try to check in with the forum.

You can zero the test lead in the software by performing a zero offset in the software which involves shorting the leads together by connecting the two ends.

The other thing to bear in mind is where you're measuring across the resistor. Try to make sure your as close to the terminals on the resistor as possible to avoid any unwanted resistance which may be introduced by the additional wiring.

Just a couple of pointers and I'm sure Steve will add anything else.

Kind regards

Ben

[Steve Smith]

Hi David, I hope you are well? Thank you for the post and thank you Ben too

I guess my question is, are you using PicoLog or PicoScope in the scenario where you have 15 mA before connection?

If PicoScope, Ben has described the zero offset feature that will hopefully resolve the concern and I can now add an attachment to help with interpretation (Attachments were not loading recently)

Given we are measuring tiny voltages; 1.5 mV in the case of your 15 mA “zero value” (0.015 A * 0.1 R = 0.0015 V or 1.5 mV) we need to ensure we do all we can to minimize the impact of environmental noise as just waving the probe in free air with no connection to the vehicle may acquire more than a 1.5 mV in ambient noise.

With channel A options panel open choose the relevant voltage range for your resister.

Image 1

Remember, approx. 3.1 V drop across the resister would be the maximum for a 100-Watt resister (3.1 V / 0.1 R = 31 A) therefore (3.1 V * 31 A = 96.1 Watts)

Next, select “Zero channel offsets” and join channel A test lead signal wire to ground wire (join 4mm banana connectors together) as instructed below

Image 2

Select “Continue” and wait for the scope to perform the zero offset. Finally, select Bandwidth limit to “On” to remove any high frequency noise from your measurement process.

You may also choose to lower the sample rate as typically we are do not require a high sample rate to capture parasitic drain.

A final tip is to keep test leads/resister away from sources of noise as this will once again affect your average parasitic drain value if we are not at true zero

Moving onto PicoLog, if you are using this App then zero offset is not included and so we need to be sure you can zero channel A as described above (using PicoScope)

If zero offset is functioning in PicoScope, we know our measurement hardware and software are functioning correctly. If however after zero offset in PicoScope you still have an offset then we need to investigate further (i.e., try another channel)

Given PicoLog utilizes a very slow sample rate (1 S/s) this has the beneficial side effect of removing noise; note, the same rules still apply regrading keeping test leads/resister away from sources of noise

I am going to raise a New Feature Request for the software team to consider zero offset within PicoLog and hopefully resolve your concern in a future build

I hope this helps, take care…….Steve