Help getting started:: Runtime / Lux Data Logging

I am wanting to get a lux/runtime setup going soon.
I have been wanting to get a LM631 Light Meter for a long time now, sence it seems to be the most used meter here on CPF.
However, I am not sure if I will be able to data log well with it.
It does have a mV analog output, but I am not sure what it will compatable with.

i have been talking to Roy, and he has pointed out this Radio Shack DMM that has software included, that is much like his, for graphs and data logging.

Does anyone know if I would be able to use the LM631 will work with this DMM correctly?

Roy said he uses this adaptor with his DMM. web page
Would that work better?

Basically, I am wanting to display a chart, that has lux on the left,, and time on the bottom.

Any help would be great, thanks guys.

-John

Yes, that meter features "Analog output for monitoring and charting", just what you want.

As would Roy's suggestion for less $$ (but it wouldn't have it's own display, wouldn't work 'stand alone').

Doug Owen

Says HERE , that it is a 2.5mm headphone jack output,,, simple enough, I can wire that up.
Then it says 1mV = 1 Lux.... Will I be able to tell the software that?
So that it is displaying the actual Lux on the left of the chart?

I know alot of them just put a number there, that is just a representation of Lux, but not the actual Lux reaading.
I am wanting the actual Lux reading to show up on the left of the chart. And time on the bottom.

Just get the proper instrument in the first place, instead of inducing error from the lightmeter, then stacking it on top of the error in the DMM.

Same company as one of your listed ones, higher end model:
http://www.electrical-contractor.net/The_Store/EX/407026.htm

Accuracy is +/- 4% + 2 digits of full scale.

Manual here: http://www.extech.com/instrument/products/400_450/manuals/407026_UM.pdf

Works fine, I've got one.

Meterman LM631 "Total Accuracy" for CIE standard Illuminant A (2856K) is +/- 3% rdg + 10 digits.

Jar,,, I saw that one also, while it does look very nice, its quite a bit more than I wanted to spend on this. /ubbthreads/images/graemlins/frown.gif

By the time I buy the meter, and then the optional software, its about $230

Does the Meterman have different light sources? If you are using the standard tungsten (Illuminant A), the reading is in significant error.

Toss in an extra +/-0.3% + 4 digits for that radio shack meter.

The Extech I mention is 135.88, then add cost of simple RS-232 cable:
Mfr.'s Part #: 407026
Allied Stock #: 631-0041
Manufacturer: EXTECH, INSTRUMENTS
Description: Meter, Foot Candle, Lux

http://www.alliedelec.com/cart/partlookup.asp

Heavy Duty Light Meter with PC Interface

Enhance accuracy by selecting one
of four lighting types plus PC interface

% displays differential from reference point
?ZERO? Re-Calibration
Enhance accuracy by selecting lighting type Tungsten/Daylight, Fluorescent, Sodium, Mercury)
Data Hold, Min/Max/Avg readings
Built-in RS-232 PC serial interface

You can buy the Extech software and cable kit (at 69.00), or just make your own, log the data, and import into Excel. If you are savvy at Excel, you can bring it right in as it is happening, and have the graph go realtime.

Yes, that's how it works. Typically the analog output is zero to 200 mV from 0 to full scale reading on whatever range the meter is on. You set your DMM for it's .2 VDC range and bang away. The light meter, your DMM and the number sent the computer will agree within a count or so.

Given that there is a many percent error in set up and reading of a given flashlight, I wouldn't worry about possible errors less than that by not blowing the rent money on 'a fifty dollar shine on ten dollar boots'. The rig you suggest is clearly accurate enough for our needs here. If you want to get hung up in light color compensation (rather than 'what's brighter that what'), the k factor numbers are out there, correct it post data collection.

Point is, I'm sure to read a different number of Lux or Fc for exactly the same flashlight as you do, the key is to make the data set useful. Or maybe it's to stop talking about it and start collecting that data?

Doug Owen

Jar, The cheapest I can find that Light meter is HERE. For $169, then as you said, the software and cable are another $69, for a total of $238.

Now, I wouldnt be surprised if this setup is more accurate than the one I mentioned,
I do not think the LM631 has settings for light types. Here is the Data Sheet on the LM631.

As Doug said, I think the LM631 will be accurate enough for what we need it for here at CPF.
I mean, lets say its off 3 to 6 Lux... unless I am taking readings on very low power lights all the time, its not gonna matter.
And, I doubt its gonna be off that much, probably just a lux or 2.

Doug, yes, the LM631 says its one mV = one Lux, thats pretty simple.
What DMM are you using? For the most part, I think that DMM I mentioned will be fine, its basically just like Roys, and his are great.
But, do you think it will keep a log of the data, in a text file type format? Or something I can import into excel?

I have two such DMMs, their software outputs spreadsheets (excell). To make a run you need to have light meter, DMM and computer all running, the DMM doesn't store it up.

Doug Owen

eBay is your friend: extech

I own a LM631 purchased from eBay for about $40

Pablo

The software tht came wilth my RadioShack 22-805 DMM does two things.....does the plots you see on CPF and creates a text file of the all the collected data. If you look in the upper right of the plots you will see the file name (which you have to create prior to plotting) the data is stored under. I'm no spreadsheet expert, but you might be able to import the text file into a spreadsheet and make your own plots.

My logging and plotting software ONLY reads the DMM and thus the vertical axis of the plot will always be in units of volts or amps and never Fc or LUX. Thus I always add a statement that 1mV is eauivalent to 1Fc. And since I measure at one foot then 1Fc@1Ft = 1LUX@1M.

By the way.....there is a model fo the Extech Light Adapter that is calibvrated in LUX. Thus if you measured at one meter, then you'd have 1LUX@1M = 1Fc@1Ft

You guys have been utilizing the LM631 CIE Illuminant A (2856 Kelvin temp) meter to measure white LEDs with?

You do know most white LEDs are over 5600K color temp, right?

So much for incandescent comparisions to white LEDs.

Ack!

I asked this question to a Wavetech rep about LM631:

I use the LM631 for personal testing of flashlights, spotlights, etc, utilizing led, xenon, and halogen emiters or bulbs. Are the readings for led lights confusing the LM631's sensor for the CIE photopic curve? Can I add or subtract lux, or fc for halogen, xenon, and led readings? Thanks,

Bill Rees
CPF #3606

and got this answer:

As long as the wavelength is within the visible spectrum, the source (LED, halogen, etc.) doesn't matter.



-----Original Message-----
From: [email protected] [mailto:[email protected]]
Sent: Sunday, July 11, 2004 2:53 PM
To: [email protected]
Subject: LM631 testing led lights

PEU, thanks for the Ebay link.
That is a meter that Newbie pointed out to me the other night, he has that one.

I emailed the seller, to see if the software is included, if it is, thats a great deal, and I will get it.
He mentions the software, but I dont know if he ment it is included..
Hopefully he answers, sellers seem to never answer my emails. /ubbthreads/images/graemlins/frown.gif

[ QUOTE ]
jtice said:
For $169, then as you said, the software and cable are another $69, for a total of $238.


[/ QUOTE ]

Man, don't waste $69 on the cable! You can get the 1/8" plug for the MeterMan at Radio Shack, and any old speaker wire will work for the cable. Add a 1 mega-ohm resistor across the input wires to eliminate noise as the input impedence of the Volt meter is so high. The software comes free with the Radio Shack meter..

Lambda,,,

The cable AND software, are $65.

I have decided to go with, the Meterman LM631, and the USB Labjack data logger.
I have already ordered the LM631, I will get the logger next month.

I really didnt want to spend $120 just on the logger, but, it will be worth it in the long run, so I can log multiple inputs with it.

Thanks to all of you, for your help.

-John

[ QUOTE ]
jtice said:
Lambda,,,

The cable AND software, are $65.

I have decided to go with, the Meterman LM631, and the USB Labjack data logger.
I have already ordered the LM631, I will get the logger next month.

I really didnt want to spend $120 just on the logger, but, it will be worth it in the long run, so I can log multiple inputs with it.

Thanks to all of you, for your help.

-John

[/ QUOTE ]
John:

I have a LM-631 and have used it with a Fluke 189 DMM which does data logging but that really doesn't matter. Any DMM will show that analog output of 1mV=1 lux or 10mV=1 fc doesn't hold true for all scales. It's not a big problem once you know what's going on, the manual is just wrong. I don't remember which scales are wrong but for instance: 100 lux should output 100mV but it doesn't, it may read 10mV or 1000mV. Before somebody mentions the X10 scale, it wasn't the highest X10 scale, I think that it was the full scale, no decimal point that was wrong, now that I think about it!

I called Meterman about this and it took forever them to understand what I was seeing on the meter. After finally getting my point across, they said that since they actually don't make the model, a third party does, they doubt if it will ever be looked at. If you look at EXTECH light meters, you find a meter that looks just like the LM-631 with a different colored case and costs much more!

I got mine here with a free cheap DMM: http://www.circuitspecialists.com/prod.itml/icOid/3401

You all just wander down to your nearest RadioShack and pick up the RadShack #22-812 auto-ranging multimeter that works alone or through the computers RS-232 port. It happens to be on sale for $59.99 until 7/29/04.

Then you buy a Extech 401021 light adapter and believe it or not with the software that is included with the RS multimeter you are in the light testing business real cheap.

The setup works really nice.