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I need a good data logging DMM -- 1.5kV Range

  1. May 28, 2016 #1
    Hello everybody,

    I am currently working on a research project and need to record the IV curve of a plasma discharge. Our current setup is pretty cool. We just have a web camera setup and using python+OpenCV we make meter reading inferences based off true/false statements based around what segments of a 7 segment display are on. The problem is that sometimes the program confuses 0 and 8, 5 and 6, etc. We added statistical corrections but even then the hysteresis/lag between when I control the PS to the plasma discharge to the DMM's is too high.

    I need 2 meters (or 1 if possible) that can record and save the values I'm measuring either wirelessly, USB, etc. One to measure voltage that can reach up to 3kV (up to 1.5kV is manageable though) and one to measure current in the microamp range (as low as 10 uA).The current meters I have is a Fluke 116 for current measurement and a BK survivor 2860A which ironically busted a cap and died today. Anything around the spec level of those is okay. In terms of price I cant see my department paying over $1,000. Less than $500 is ideal. I'd prefer a vendor that gives educational institutions a discount.

    I've been searching for a while and I like the fluke Connect brand especially the FC 3000 but they dont seem to have a line whose voltage range is above 1,000V

    Any help is appreciated I looked at the excel sheet but didnt find a model with a voltage range
     
  2. jcsd
  3. May 28, 2016 #2

    johnnyrev

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    What is the maximum current you would be dealing with? If the current remains low enough you can use a high voltage probe, like those used with CRT high voltage sections, to allow for the use of any 1 KV limit DMM with the standard 10 MOhm internal resistance, since those probes usually measure up to about 40 KV. You could pick up one of those and a couple of new meters well within your $500 budget, if the option would work for you.

    EDIT?: Nidum originally posted "potential divider," but his post vaporized. I suggested his solution would be right for you rather than laying out more money, and said to just get some good inexpensive data loggers. Like I said earlier you can get a couple that will save many points of data with USB connections for under $500. It all depends on the plasma circuit, whether that will work or if using a voltage divider will kill your setup until it is removed. The probe mentioned above will have a high enough inductive reactance to keep that from happening, as long as the current isn't too high for it to handle. Fluke makes one, their data sheet should tell you what it will handle.
     
    Last edited: May 28, 2016
  4. May 28, 2016 #3

    jim hardy

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    Today's digital scopes have communication - might the answer be already in your test equipment locker? A high voltage probe shouldn't be too expensive.

    Tektronix used to sell an active pass-through current probe DC to 50mhz. I dont remember its lowest range, but i do remember winding a multi-turn coil to extend it.

    For a brief transient might an ordinary AC pass thru current probe work ? Integrate voltage and you have current.
     
  5. May 29, 2016 #4
    Oh a voltage prob I might actually have one laying around, but do you know of any products that where instead of a prob its leads that can plug into the banana portion of a bnc to banana converter. I don't have a schematic on hand but I'm measuring the current between the power supply and sample contain the sample discharge. The current shouldn't exceed 5mA. It usually hovers around 10-400uA unless there's a spark from a bad sample. My biggest concern right now is safely connecting the probe and finding an amp meter. For whatever reason some amp meters (maybe due to internal resistance?) effects the circuit in a way that I cant get discharge. Now that I think about it though they my have just been broken.
     
  6. May 29, 2016 #5

    johnnyrev

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    Ammeters get blown all the time through carelessness. Jim's scope recommendation would have BNC connections.
     
  7. Jun 13, 2016 #6
    Any other high voltage scope recommendation the one recommended is $1,000. I don't have access to that type of budget.
     
  8. Jun 13, 2016 #7

    jim hardy

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    to measure 1500 volts, or to measure current carried by a wire that's at 1500 volts ?
     
  9. Jun 16, 2016 #8

    johnnyrev

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    ^ With 1.5kV, use the voltage probe. It depends on whether there was a scope in your locker as Jim suggested. You may be able to afford a DMM with a scope readout. But since the project is probably time sensitive, you might be needing local help soon!
     
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