Meter To Measure Current / Calculator Suggestions

I find that I very rarely need to measure current (and I've been working in electronics for over 40 years).

However, most DVMs these days will measure currents from 200 uA to 10A full scale, which should cover almost any requirement.

HP3478A will do 3 amps. Has 1uA resolution on 300mA scale. My experience has been that whenever I really, really needed ACCURATE low current measurements, there were a bunch of other issues. The meter resolution was the least of my worries.

HP calculators are nice if you have dedicated calculations and absolutely need portability. But a laptop is cheaper. Desktop cheaper still. There are some mighty nice math packages available. mike

Mike's right. How far do you ever wander from a PC?

BTW, sci.electronics is not a valid group.

Here is a circuit that looks a bit like an Instrumentation Amplifier with the property of no voltage drop. It is of course good only for small currents ----+-|+\ | ___ ___ | >- +----)-+-|___|-+-|___|-+ | +-|-/ | | | R1 | R1 | | | |/ .-. | | | === | | | | | | | GND | | | |R | | | | | '-' | | | |\ Ue=0 | | | | +-|+\ Uout | +-------+ | | | >--+----o | | | | | +-|-/ | | | .-. | | | |/ | Uout=2*R*I | | | | | | | | | | | |R | | | | | | |\ '-' | | | | | +-|-\ | | | ___ | ___ | V | >- +----+-)-|___|-+-|___|-+ o-----

How accurate is ACCURATE? What kind of resolution is acceptable? High accuracy usually means high resoultion also. The HP 428B DC Current Meter is an older vacuum tube technology instrument, but it has a clamp-on probe that will let you measure current without having to open the current path to measure. Full-scale ranges from 1ma to 10A.

I have a hung chang analogue meter that measures (dc) current from 5 mA to

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Just get a cheap meter that measures the low end. All you then need to expand the top range is a shunt resistor, you should be able to wind your own as the value will be very low for fsd readings of 5A or more.

E÷R has always done it for me, but I did use a current range checking for car battery leakage with ignition off once.

FWIW forget using the current ranges, you'll only end up wrecking the DAMN DMM

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A reasonable DMM will have an internal replaceable fuse for the current range to protect the meter.

OK, you guy's with the Harbor Freight got to me and I just completed the order for (5) of the $2.99 meters. I was going to order more and put em on Ebay. I will have some to give to other's when they ask some questions about electronics. Thanks!

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Get a DMM with current measuring capability up to 10 or 20 amps. (It seems that those are the two most common sizes for the high side of the current measuring capability.) On the low side you don't need to measure down to 1 uA. Standard for these meters seems to be 200 uA. Almost any decent DMM you buy has current measuring capability. Even the $2.99 (on sale) Harbor Freight meter that Roy mentioned measures 200 uA to 10 Amps. I think it may be on sale now. By the way, that is a great buy - it even comes with a 9V battery included. It's great for non-critical measurements, and for "kick-around" use where if it gets damaged or lost it doen't matter. And the thing is surprisingly accurate.

If you do enough messing around as a hobbyist, you will certainly run into occasions where you want to measure the current.

Ed