microcurrent for high voltage - Page 1
Forum section: electronics / testgear

author: vindoline
author_rank: Unknown
timestamp: June 21, 2014, 06:34:28 pm
content: I'd like to know what the voltage input range is for the microcurrent gold. I'm interested in characterizing the current consumption of some high voltage circuits 400 - 1200V! that consumer very low currents. Thing such as ion chambers, geiger tubes, scintillation probes, photomultiplier tubes, etc. I have a feeling that even a microamp at 1000V may let the magic smoke out!. Thanks in advance.

author: plesa
author_rank: Frequent Contributor
timestamp: June 21, 2014, 07:22:25 pm
content: Just add protection circuit to limit maximal input voltage (e.g two anti parallel low leakage diodes). You can add resistor to minimize the maximal current in case of electrical breakdown.For higher voltages you can also add gas discharge tube.See attached Keithley document.

author: Marco
author_rank: Super Contributor
timestamp: June 21, 2014, 08:45:54 pm
content: Quote from: vindoline on June 21, 2014, 06:34:28 pmIf there is 1000 voltage across the microcurrent it won't be conducting a microamp ...In normal operation nearly all the voltage will be across the ion chamber etc. The problem is that they can arc ... and when they arc the current is not a microamp either.

author: vindoline
author_rank: Unknown
timestamp: June 22, 2014, 10:08:04 am
content: Quote from: Marco on June 21, 2014, 08:45:54 pmThank you for the reply. That's basically what I'm wondering about, will there be arcing across the traces or components in the microcurrent if it's used at high voltages. I appreciate your point that there will be little voltage drop across the microcurrent. The typical type of power supply I'll be using isn't able to source very much current. It's generally less than a milliamp.

author: EEVblog
author_rank: Unknown
timestamp: June 22, 2014, 11:05:04 am
content: If the uCurrent has excessive voltage across the input shunt resistor, then you are using it wrong!

author: EEVblog
author_rank: Unknown
timestamp: June 22, 2014, 11:07:21 am
content: Quote from: vindoline on June 22, 2014, 10:08:04 amIt can't if used correctly. It is an isolated battery powered device. If there is an arc across some component then you have a physical setup problem of some sort.

author: vindoline
author_rank: Unknown
timestamp: June 22, 2014, 11:19:57 am
content: Thank you Dave. Sounds like it should be fine

author: Marco
author_rank: Super Contributor
timestamp: July 05, 2014, 12:29:22 pm
content: Quote from: vindoline on June 22, 2014, 10:08:04 amOops, missed the reply ... better late than never though :You misunderstood what I was trying to say ... you seem to believe that the high voltage makes a difference to the uCurrent in normal operation, it doesn't because your DUT takes the voltage. The problems only occur if your DUT goes low impedance, like for instance an Ion Chamber arcing or if your power supply ramps too quickly ... if it arcs the uCurrent could destruct instantaneously regardless of how much current your power supply can deliver, simply from energy stored in (stray) capacitance. Simply depends on how much energy there is, the input resistors and the protection diodes inside the opamps provide some protection.So in summation, you don't need input protection simply because you use high voltages ... you need input protection if your DUT has the potential of going low impedance. What kind of input protection depends on how much energy you can expect to dump across it.