Power Consumption of a 4423 scope

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Power Consumption of a 4423 scope

Postby hexibot43 » Thu Oct 23, 2014 6:07 am

I just got a new toy. I ordered a device called a PortPilot quite a while a go. Finally arrived this last Saturday. I had been having real trouble getting my 4423 to work properly, and so was looking at anything to help me diagnose what was going on. I thought it might be interesting data for people to take a look at.

PowerUsagePicoScope4423d.jpg


It is a pretty self explanatory graph. Current and Voltage recorded with the use of an inline device between my laptop, and my scope. http://portpilot.net/ If anyone is interesting in checking one out. This device has a third USB connection that can be plugged into a pc to log and view the data. I had yet another bad USB cable.( Not the Pico Cable, the data cable for my new PortPilot.) I was having mixed results with this new tool. And then suddenly it wasn't being recognized at all. The display on the unit was working but the data logging feature just wasn't working. Swapped in a new cable and threw away the old one. Problem solved.

I had some trouble getting the Scope to complete enumeration. With the PortPilot in-line the scope would hang while attempting to connecting the scope. I'm still not sure what was going on with that. It appears to be working well now. Perhaps it was my bad USB cable causing some problems.

I haven't taken any reading with just the Laptop battery and no mains connected. I'm assuming things shouldn't change though.

The graph starts out with the scope merely plugged in drawing around 50mA. No software running. Next You can see where the Voltage drops off and the Current climbs. This is where the software is started. Suddenly we are at 470mAs and our USB voltage has dropped to about 4.903 volts. The graph also shows what happened as I turned each additional channel on. The voltage would drop off, and the current draw would increase. I haven't tried to figure out what more I could do to load the USB port with the scope. But it is just barely within the upper Current draw limit of the port (But it is within). I can see where one computer might work well and another not so well.

Just thought I'd share my findings. Maybe someone else might find them helpful. I have become very aware of how critical good, make that really good, USB cables are. I must also say that my testing didn't take readings right at the scope. They were taken between the computer and the USB cable. So that cable to the scope better be really good.
Last edited by hexibot43 on Sat Oct 25, 2014 3:59 am, edited 1 time in total.
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Re: Power Consumption of a 4423 scope

Postby Steve Smith » Thu Oct 23, 2014 11:23 am

Hello Hexibot and thank you for the detailed feedback

With regards to
hexibot43 wrote:I had been having real trouble getting my 4423 to work properly,
.

Can you help here with the symptoms?

Have you experienced continual/intermittent failure of the scope to connect upon launch of the PicoScope software?
(Could you send the trace file for such an event)

Or, have you experienced issues once the scope is running during capture?
(Could you send a psdata file for such an event)

You mentioned
hexibot43 wrote:I had some trouble getting the Scope to complete enumeration. With the PortPilot in-line the scope would hang while attempting to connecting the scope. I'm still not sure what was going on with that. It appears to be working well now. Perhaps it was my bad USB cable causing some problems.


The USB cables in question, were they the Pico Blue USB cables?

If so have you had/suffered repeat failure of Pico Blue USB cables? I would be very interested to recover your Pico blue USB cable if this is the case to pass onto engineering for evaluation.

I stress the use of the Pico Blue USB cable as they are a high quality cable, contain additional strands of cable, complete with improved grounding. This ensures the integrity of the signals measured, during transfer to the PC (Low noise level) along with the power supply/ground.

What are the length of the USB cables under test?

There is a general acceptance in the field of USB 2.0 communication that the absolute maximum USB cable length that can be utilised is approximately 5 metres before the integrity of the power supply and data begins to suffer. (5 meters being the industry standard)

Given our scopes are powered via the USB we have to err on the side of caution and for this reason we have opted to manufacture a 4.5 meter USB 2.0 extension.

Many thanks Hexibot for the detailed information supplied as wht you have highlighted is the importance of the quality of USB link and how cable quality has a direct effect on performance.

Take care......Steve
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Re: Power Consumption of a 4423 scope

Postby hexibot43 » Thu Oct 23, 2014 2:17 pm

Steve et all,

My 4423 is working very well now. All my problems were from bad cabling. My new cable from PIco is working great. Seems so obvious now. But I spent many months with a scope that worked sporadically. I had plugged other devices into the same cable I was using with the Picoscope and they worked just fine. This had given me the false idea that my cabling was good.

What I am trying to show is how how critical the cabling is between the scope and the computer. The Scope is very demanding in relation to the USB standard. This is not a bad thing. It simply is. And because of this it is absolutely critical to have the best cables you can get. I can also image how a poorly designed PC could be problematic as well.

I've done a lot of reading on the subject of USB ports and power. http://electronics.stackexchange.com/questions/5498/how-to-get-more-than-100ma-from-a-usb-port Has some good insight and just barely scratch the surface of dealing with USB.

Now that I have a good way to look at the power lines of the cabling, I'd really like to have a way to look for failings of the data lines. I'm thinking it is too bad that these same cables are used with the cell phones of today. I'm guessing my most recent failed cable is probably due to one of my daughters swapping out the cable they use to charge there phone with one of my cables. Not telling me the cable is no good, or throwing it away. Just swapping it with mine so that I will pull what is left of my hair out. The cable that failed me this time was not the Blue Pico cable. It is working great. This is the cable that would plug into my new PortPilot and a second USB port on my PC for data logging of power usage.

I am going to continue my testing. All those months of frustration thinking something was wrong with my scope is still weighing on me.
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Re: Power Consumption of a 4423 scope

Postby hexibot43 » Sat Oct 25, 2014 5:07 am

This little tool has lead me to really see the weaknesses. I couldn't figure out why when I was testing at home things worked easily and when I got to work everything would have problems. My work computer was being stubborn. If I plugged the PortPilot in the Picoscope would not work with it in line most of the time. If I could get it to work it would continue to work though. I have two identical IBM ThinkPad T60s. One at work and one at home. The PortPilot would work every time at home. I pulled out a powered USB hub. I then plugged it in between my computer at work, PortPilot, and finally the Picoscope. With the Powered Hub in line I started to get consistent results. PortPilot and Picoscope both working well. I had hoped to be able to capture the issue with the PortPilot in the form of a log file, but I guess in the end I got the same result. Some weakness in the USB port of my laptop at work showed up with the little increase of current drawn by the PortPilot. At least this is my assumption. So not only did I have cable problems, but problems with one of my computers too. I ended up swapping computers. No big deal to have the USB hub on my workbench at home. But having to power my Work laptop along with a powered USB hub from mains all the time would really be annoying.

I did some logging with the PortPilot with the USB hub in line. Now I'm questioning The Power supply of the USB hub. It is working consistently as far as the devices attached to it now. But I would really like to hear what others think of the data I gathered. The voltage on the USB Power is much less consistent. Or at least it appears that way to me. Noisy? It was brought to my attention that the voltage is really only varying 20mVs which is acceptable. Although it appears noisier the range of change is small.

WorkingWithPoweredUSBHub.jpg


So many ways for the power to go wrong... I am really thinking that perhaps I should take the load off the USB port of the good computer. My other computer shows that this port is probably already weak, even though it is currently working. Maybe it is time to swap out the T60s for something with a more robust USB port. The next question is what would that be? I see the requirements of the new USB3.0 allows for current draw of 900mAs . Almost double the that of USB2.0. That should give me some breathing room, and hopefully end up not stress the port too much. Then I'll be ready when I finally break down and get the New Picoscope....
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