Re: Wideband ammeter

On 23/03/2025 2:59 pm, Sergey Kubushyn wrote:

Bill Sloman <bill.sloman@ieee.org> wrote:

On 23/03/2025 12:49 pm, john larkin wrote:

>
How about thermal imaging a surface-mount resistor?

>
Why bother? Measuring the voltage drop across the same device is easier,
and just as fast, if not faster.

 That depends on what you actually want to measure. And "wideband" makes it
even more difficult.

But John hasn't spelled out any advantage that thermal imaging might offer.

Wideband current shunts made for AC-DC transfer are all of very special
construction and cost arm and leg.

Mainly because it's a small and specialised market. You need a resistive material whose resistance doesn't change much as it warms up and wideband means that you need something flat and compact.

If you want to measure the voltage drop
over those resistors, without making AC-DC transfer, you're up to another
challenge, measuring the AC voltage. Should start from the definition, what
IS the AC voltage? What the actual number your measurement shows means and
so on.

Measuring AC isn't - in principle - different from measuring DC. You just have to do it more frequently.

Look at e.g. not all that precise but much better than most LT1088 chip,
long obsolete. There is another one, proprietary and much better precision
inside e.g. Fluke 5790A Standard (which is a misnomer -- it is actually an
AC and DC voltmeter, 10x more precise that the venerable HP/Agilent/Keysight
3458A).

Nothing to do with thermal imaging.
--
Bill Sloman, Sydney