Lab power supply - readback accuracy (NGM202)

[hcglitte]

Hi,

I need some help to understand some datasheet parametes.

Looking at the datasheet for Rohde & Schwarz NGM202, the readback accuracy for current is:
±(% of output + offset): 10 mA range: < 0.05 % + 15 μA

The resolution in the same range is 10 nA.

I interpret this as if my load is known to be 15 uA, the readback could actually display 0uA.
What is the point of having 10 nA resolution when the offset is many orders of magnitude higher?

Using the display to read a sleep mode MCU current would also not make much sense, given that interpretation I have.

Any clarification is much appreciated, thanks.

[Kleinstein]

High resolution ADCs (e.g. 24 Bit SD type) are pretty cheap today, but the guaranteed linearity is not that great. There are also offset errors, that may not be fully adjusted. 15 µA error specs with 10 nA resolution is still pretty unusual. Much of the error is likely just an offset that may however dift somewhat. So one can likely get much better readings than that - just no specs / calibration to support this.

[exe]

Higher resolution may help with relative measurement.

I interpret this as if my load is known to be 15 uA, the readback could actually display 0uA.

You mean a "deadband" when it doesn't show apparent negative values due to offset error? I'm not sure about this. It may or may not work this way. I'd say it depends on schematic and firmware. It seems this thing can sink current, so I'd expect it knows how to deal with "negative" currents. They may also put a conservative spec "just in case". But it's best to confirm with an R&S representative if this is really important.

[hcglitte]

Hi,

No, I mean that it can show 15uA of error in both directions.
For example: 30uA load could be shown as 15uA on meter.

List price at Farnell is €4,850.00
I can get it for 3,300 Euro. Wondering if I should jump at it.
I like the logging capability and that it can sink current - as well as emulate a battery.
Still a lot of money though.
Not sure about alternatives which offers the same functionality for this price point.