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| Device for nA Measurements ? |
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| mawyatt:
--- Quote from: Performa01 on January 03, 2023, 03:26:33 pm ---Most DMMs with 10 Mohms input impedance can be used for this in principle. Just use the voltage range, e.g. 200 mV instead of the current ranges. This becomes a 20 nA range and you can measure down to 10 pA with a 20000 count meter. Some (especially true bench) meters have an unexpected high input current up to 1 nA. You can detect this by measuring the open circuit voltage with 10 Mohm input impedance; thus the meters own input current. If this is anywhere above 50 pA (= 0.5 mV), then the meter isn't usable for this purpose. Of course, the "correct" way to do this is using an electrometer; this allows you to measure down to the femtoamperes... --- End quote --- There's another good way to measure the DMM Input Bias current if the DMM has the usual High Z Input (10G) feature on lower voltage ranges. Us a small 1nF or 10nF quality low leakage film cap (Polypropylene, Polystyrene), place the cap across the DMM inputs and short the cap. Remove the short and time the voltage ramp to a voltage within the range of the DMM setting. The input bias is calculated as Ibias = C dV/dT, where C is the used Cap, dV is the delta voltage reading and dT is the delta time to reach said voltage. We use this simple method to periodically check our various DMMs to "see" if the input has been damaged (dramatic increase in bias current). Just did so recently with three KS34465A, DMM6500 , AG34401A, HP34401A and SDM3065X, results were (11, 5, 4), 8, 25, 5 & 71pa respectively using a 10nF Polystyrene Cap. Best, |
| DavidKo:
Even with most Benchtop Multimeters it is not possible. Have you checked the tables in the pinned topic? Other thing is that nowadays they want to pay you premium. Old meters had uA ranges and that UniT have the same 10nA resolution as HP 34401A (please do not comment this sh.t ;) ). Below you can see comparison between old tech HP 3457A and newer tech HP 34401A. HP/Agilent 34401A is a downgrade in this case HP 3457A (you can see 10pA through GPIB) |
| tooki:
--- Quote from: Nicole01 on January 03, 2023, 03:44:10 pm ---I mainly want to Measure Voltages in the 1-30 Volt Range. I have also seen that you can install a Resistor in the Circuit and then Measure the Value. I don't want this, i want to Buy a finished Device. You're right, there are many different Devices. With many, however you also Pay for the Name of the Manufacturer. That's why I'm asking if there might be a Manufacturer who isn't that well known and the Price is okay :-// --- End quote --- This type of instrument isn’t exactly super-common. You’re not just “paying for the name”, you’re paying for the expertise in designing these high-accuracy, low-sales-volume items. If you want one cheap, get a used one. That’s a fantastic way to save money on quality test gear. I’ll choose an old Keithley over a new no-name any day. |
| Nicole01:
DavidKo thank You for the topic Link :-+ I think I didn't phrase myself correctly. You are right, many Multimeters can Measure in the µA and nA Range. But not very far down. I want to Measure at least to 1 nA. Many Multimeters only Measure 2 Digits after the decimal Point. If I now want to Measure 1 nA, this cannot be Displayed. The Price is not that Important, the main thing is that I have correct Results. |
| Someone:
--- Quote from: Nicole01 on January 03, 2023, 09:21:14 pm ---I want to Measure at least to 1 nA. The Price is not that Important, the main thing is that I have correct Results. --- End quote --- So where is the confusion? Look through data sheets to find devices that will meet your accuracy specification. DMM6500 is probably the cheapest thing in that space. From there it is off into SMUs and Picoammeters. All those devices have limitations that may be "no go" for your unspecified end use (and other functions that may be value add) so it is almost impossible to provide any suggestions. |
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