Can a multimeter measure current directly @ the diode/testload?

[LazyBeam]

So i recently found out my multimeter (analog) does not measure mV... not too helpful for using my homemade test load.
However it does measure mA with a 0-50 and 0-250 range.

Can I measure mA directly across the test load (or laser diode) terminals?
Would i have to measure the mA across the 1ohm resistor?
I don't think it would matter where I measure it but I thought I would ask to be safe.

If I can measure mA directly... I may use the test load to get my driver set "close" to desired output and fine tune it once it's connected to the actual LD.

 

[charliebruce]

Put the test meter directly in place of the 1 ohm resistor (removing the resistor - put the meter in series with the load) and it will show the current.

 

[LazyBeam]

Put the test meter directly in place of the 1 ohm resistor (removing the resistor - put the meter in series with the load) and it will show the current.

Instead of pulling the resistors off of my board can I just put the multimeter in series with the negative test driver input
Run the current through the multimeter into the unmodified test load?

I used 4X 1ohm 1w resistors (2X twin parallel resistors in series totaling 1ohm) so they can handle more power.
I'd rather not have to pull all of them off. :yabbem:

 

[CrazyMonkey]

You mentioned your meter only goes to 250ma, so don't do that unless your actually running it below 250ma. Really though, you need a cheap meter that reads mV, or at least can measure more then 250ma.

 

[LazyBeam]

For now I'm only working with a AW210 (4X bluray) so the MA will only be set to ~170-175.
It's an old radioshack multimeter I've had just about forever. Mainly just to work on my car and other stuff so for that it's fine.

I might ask someone at work if we have a nice fluke that could be borrowed...

 

[boscoj]

thread jack sortof - do they make a DC clamp ammeter?

 

[charliebruce]

thread jack sortof - do they make a DC clamp ammeter?

I doubt it, and definitely not at the high accuracy you'd need for a laser. The closest thing we have to a "nonintrusive" measurement is a shunt resistor.

 

[boscoj]

why is it they can make an AC one, more amps/cheaper device? must be the waveform or something . . .

hey Charlie ! I did my A levels in England . . . have family in Devon !!

I doubt it, and definitely not at the high accuracy you'd need for a laser. The closest thing we have to a "nonintrusive" measurement is a shunt resistor.

 

[charliebruce]

why is it they can make an AC one, more amps/cheaper device? must be the waveform or something . . .

hey Charlie ! I did my A levels in England . . . have family in Devon !!

Simple current clamps use the transformer/motor effect to measure, which has to take a "rotating"/shifting field to work properly. Hall Effect sensors use a different principle to measure current, and are more expensive but can measure DC (and lower currents) too.

I just did GCSEs, now moving onto the A-levels. How did you find them?

 

[LazyBeam]

I don't think hall sensors can "measure"... I believe they either "on" or "off".
At least that's how I've always seen them used... on/off sensors.

 

[BShanahan14rulz]

Just buy a dmm. I have a cheap used "craftsman" brand one from the local surplus electronics store for $10. Sure, I did have to calibrate it myself, but it's better than the analog radioshack multimeter I had before.

If you work with electronics, you just might want to save up for a better one. This one works in a pinch, though, for my hobby-grade electronics projects.

 

[charliebruce]

I don't think hall sensors can "measure"... I believe they either "on" or "off".
At least that's how I've always seen them used... on/off sensors.

I know for a fact that hall sensors can measure currents.

Hall effect sensor - Wikipedia, the free encyclopedia

Electricity carried through a conductor will produce a magnetic field that varies with current, and a Hall sensor can be used to measure the current without interrupting the circuit. Typically, the sensor is integrated with a wound core or permanent magnet that surrounds the conductor to be measured.
Frequently, a Hall sensor is combined with circuitry that allows the device to act in a digital (on/off) mode, and may be called a switch in this configuration.