Need help with LM631

I received my LM yesterday from the groupbuy organized by modamag so I immediately tried it out once I got home with my Aleph 1, Wiz2 520ma.

I'm puzzled how the Peak button works. When I toggle it, "p" and "max" is displayed on the screen, but the reading jumps to 400+lux even without any light hitting the sensor. From what I understand reading the instructions, this function will display the highest reading recorded unless a new reading exceeds the present displayed value. When I measure the lux reading, it reads around 2000 lux at 1M. When I try to take a measurement again with the previous reading still displayed, the reading suddenly jumps to 3000+ lux. I'm at a total loss what to make of this behavior. It seems as if it adds the new value to the old one already displayed.

Could anyone familiar with this light meter provide some tips on how to use it properly?

Thanks.

I also have the '631. The peak function is flaky at best, and I never use it. I find it's best to rest the light on a steady stand, and slowly change the aim to find the peak, or, depending, move the sensor around too while maintaining 1M distance.

Thanks evan9162 that's my experience as well. Some have suggested otherwise, who knows perhaps theirs works properly or they aren't being that exacting. It might take me a couple minutes to be satisfied I've hit the high.

That has also been my experience for the most part. I find that the peak function does work sometimes, depending on the range and intensity of the light, but I have not done enough tests to find out when it works best.

Will

[ QUOTE ]
Billson said:
I'm puzzled how the Peak button works. When I toggle it, "p" and "max" is displayed on the screen, but the reading jumps to 400+lux even without any light hitting the sensor.

[/ QUOTE ]
I called Meterman(divsion of Fluke) a day after I recieved the LM631 from the group buy regarding this anomoly. The technical rep that I spoke to, duplicated this with the 2 other LM631 they use to troublshoot customer questions. He said that this was normal. /ubbthreads/images/graemlins/icon3.gif

He didn't even provide a possible explanation? I wonder what "normal" means to them when it's pretty obvious it's not.

I have noticed the same thing with mine.

You can have it sitting there reading 0 to 3 lux, then press the peak button, and mine will jump up to about 30 lux.
I use the peak function still, i will let the meter 0 out, or get as low as possible, press peak, then turn on the light, waving it around slowing. Remember the meter only takes a reading once a second, so wave the light around slowly.
I reset it before each reading.

I find that USSUALLY, i will get a higher reading of I dont use peak, but you have to be watching the meter close to catch your high point.

These meters arent really good for getting REAL lux readings, but they are great for comparisons.
Though, we all use it differently etc, and our results are going to vary.

Mine shows the same behaviour. The folks who built this lightmeter seem pretty incompetent to me for not noticeing this obvious flaw.

Until I saw this thread, I'd regretted spending $160 on an Ideal-Sperry Model 61-681 light meter. Except for being yellow, it looks exactly like the LM631. In fact, I had suspected that they were made by the same company. I thought the extra cost was just due to NIST certification, but maybe the electronics are a bit better. I've not had any problems with the peak feature.

I'm sorry folks are having these problems. The only reason I posted is so that, should someone researching a meter before purchasing see this thread, they would see that there's an a very similar altenative, though a bit more expensive.

I have the Extech EA30 meter.

Depending on the range selected, it does the following:

0 at 40 fc range reads 0.00 as do all of the other fc ranges

0 at 40 lux range reads 0.02
0 at 400 lux range reads 0.2
0 at 4000 lux range reads 2
0 at 40000 lux range reads 0.02 klux
0 at 400000 lux range reads 0.0 klux

I have a Min/Max function. When I select Max, I get the same readings that I get when I first turn it on. The meter does not jump up at all.

I also have a Peak function. When I select Peak, I get the following:
0 at 40 fc range reads 0.05
0 at 400 fc range reads 0.5
0 at 4000 fc range reads 5
0 at 40000 fc range reads 0.05 kFC

0 at 40 lux range reads 0.48
0 at 400 lux range reads 4.8
0 at 4000 lux range reads 48
0 at 40000 lux range reads 0.48 klux
0 at 400000 lux range reads 0.5 klux

As you can see, there is a "count" added in when the peak function is selected.

I get very good correlation between the Max mode and the Peak mode when I subtract the "count" from the Peak reading.

Fortunately, by pressing and holding the Peak button, the system does a "calibration" that eliminates the "count" and I get the same number when using the Max function or the "calibrated" Peak function.

I don't know if the LM631 allows you to zero the peak function by holding the button down, but it might be worth a try.

I was told that the system does this to "alert" you that you are in Peak mode, and it is considered a "feature."

Tom