help with multimeter.

[Mohrenberg]

How exactly do i measure mw?
do i need a different multimeter or is there a mathematical equation i need to use to figure it out?
all my multimeter shows are ohm, ma, ac 10v, and dB -20 to +22

(it's a cheap $10 multimeter i got in the automotive section at wal-mart)

 

[phoenix77]

dB same thing as mW's

 

[Mohrenberg]

well if this thing only reads to 22 mw i'm kinda screwed then aren't i?

 

[lasersbee]

You can't measure mW with a standard DMM or for that matter an analog VOM.
I presume you are talking about measuring lasers...
You need some type of interface or a Laser Power Meter or at least a calibrated
Laser Sensor head.

If you want to, inexpensively, measure green and red lasers (tooting my own
horn)   you can have a look on eBay:-

http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&rd=1&item=150298384566&ssPageName=STRK:MESE:IT&ih=005

This item will give you a good idea of your laser's power up to 120mW.

It is no where as accurate as this Item on our web site:-

http://www.bauer-electron.com/eby/eby1wlpm.htm

Or... you can try to get a used LPM here on LPF. If you're lucky enough
to get a hold of a Kenometer... these.. I've heard are very good as well.

If you want a lab quality meter like "Electron" (a member here on LPF)
purchased recently then you'll need to fork out about $3,700.00.

It seems that quantity of money is in direct relation to quality of Laser Power Meter.

 

[phoenix77]

: : : : : : : : : : : : : : : : : : : : : : : : : : : You get what you pay for. Good lesson to be learned here

 

[phoenix77]

You can measure ELECTRICAL mW's with that meter, but as lasersbee pointed out, you can't measure mW out-put of a laser without somekind of interface

 

[lasersbee]

You can measure ELECTRICAL mW's with that meter, but as lasersbee pointed out, you can't measure mW out-put of a laser without somekind of interface

Yeah... before designing any Laser Power Meters.............. :
Believe me I tried. ;D ;D ;D ;D

 

[Mohrenberg]

no, i need it to measure the mw output on the test load, not the mw output of the laser itself

 

[lasersbee]

A test load is normally measured in milliamps (ma) or millivolts (mv)
if we are talking Laser Diode drivers??

Or are you trying to measure Electrical Power like Watts??

What exactly are you measuring?? What does the circuit under test do??

 

[Cyparagon]

mW = mA x V

 

[Mohrenberg]

it's just the test load that you use to set the driver, it's for my sony 16x diode.
because they say whatever the test load reads in mw is what your driver is set at for ma.

 

[lasersbee]

No offence intended... but... IMHO you are mistaken... I believe it probably reads:-

"they say whatever the test load reads in[highlight] mV [/highlight]is what your driver is set at for ma. "

That is the normal way to set ma using a 1 Ohm load resistor.... by measuring
the voltage drop across the load resistor (therefore mV=ma).
You just put the Multi Meter on the Millivolt scale.

 

[Mohrenberg]

ah your right...

Voltage for Red laser diodes (~2.7V) or 405nm (both Blu-Ray, and HD DVD diodes) voltage (~4.7V). Driver output current is measurable via onboard 1ohm resistor where 1mV is equivalent to 1mA output. Also features automatic output capacitor discharge resistor (defeatable).

i realise i'm just making myself look stupid now (maybe i am)

but how do i read it in mV on my multimeter?

 

[lasersbee]

You place your 2 meter probes... one on each end of the 1 Ohm load resistor.
If you were adjusting for... let's say... 190ma max... then you would put the
meter to the lowest scale that could read that max value (ie the 200mv scale).
If you were adjusting for... let's say... 1000ma max... then you would put the
meter on the lowest scale that could read that max value (ie the 2000mv or 2volt scale).

Every mV you read on the meter is the actual ma that are passing in your circuit.

 

[Mohrenberg]

my meter doesn't read in mv....
theres V- (with the three dots under the -) also V~, mA, BATT., and ohm.

 

[Things]

Usually multimeters have a Dc side, and a AC side. On mine, it has 2m on the DC side, which means mv I believe.