LeCroy scopes vs. Tek and Agilent for a specific measurement

M

Mr.CRC

Jan 1, 1970
0
Hi:

I am trying to measure the shot-to-shot energy stability of a pulsed
optical parametric oscillator. It produces 8ns, 125mJ pulses of 460nm
light, which I measure with either a 1ns photodiode, or a pyroelectric
"joulemeter" sensor which produces a several microsecond pulse whose
peak amplitude is proportional to the laser energy.

In the PD case, I integrate the instantaneous power vs. time on a scope,
then measure the peak-peak amplitude of the integral with statistics to
get energy. In the pyro sensor case, I simply measure the amplitude
with statistics.

My Agilent MSO7054 scope can do this, but has some deficiencies:

1. It doesn't automatically compute relative standard deviation which
is the important thing, so I have to type in the std.dev. / mean every
time with my calculator to see the effect. Since the OPO average energy
might change along with the std. deviation when a change is made, I
can't just look at the absolute std. dev.. I need relative std. deviation.

2. It does accumulating rather than moving average stats., so I have to
press "reset statistics" to start a new accumulation every time I make a
change to the optics to see what the effect was.

3. Ideally I'd like a trend plot of the relative standard deviation as
well.

I've been considering three other scope models, the Agilent 9000 series,
Tek DPO7000, and Tek MSO4000.

Today I evaluated the Tek MSO4054 and Agilent 9000. The Tek can do a
moving average statistic which is an improvement. But still no relative
standard deviation. It doesn't allow one to write arbitrary expressions
using the statistical measurements, only the built-in waveform measures,
so there is no way to compute rel. std. dev. with its math expression
feature.

The Agilent 9000 (I forget precisely which model) also had no way to
compute rel. std. dev., and I couldn't figure out whether it was doing
moving ave. or accumulating stats. I didn't spend a whole lot of time
with it after being sure it wasn't an improvement over the MSO4054.

Tomorrow I will see a Tek DPO7000, but after studying the manual
tonight, I'm convinced that it will also not be able to write math
expressions using the stats. So I expect I will discover that it too
can't do what I want.

A pal at work recently bought a LeCroy 104MXi-A which costs less, has
more BW, more memory, and faster sampling than the 500MHz Tek and
Agilent scopes that are about the $limit my boss can handle. He told me it can basically do everything I want! I will call LeCroy tomorrow and request a demo. They lent him one for 5 days to eval. But many people swear "LeCroy sucks." Actually, I used one in college. It had statistical calculations at a time when this was unheard of. It made easy work of some physics research that we were doing on organic photo-refractive polymers. So while the LeCroy's might not be the best electronic debugging tools (slower waveform update rate under some circumstances) for finding glitches, etc., they do seem to be superior laboratory data acquisition and analysis platforms, for a similar price class to Tek and Agilent. I will hopefully discover the real truth in a few days. Any comments will be appreciated! Good day! J John Devereux Jan 1, 1970 0 Mr.CRC said: Hi: I am trying to measure the shot-to-shot energy stability of a pulsed optical parametric oscillator. It produces 8ns, 125mJ pulses of 460nm light, which I measure with either a 1ns photodiode, or a pyroelectric "joulemeter" sensor which produces a several microsecond pulse whose peak amplitude is proportional to the laser energy. In the PD case, I integrate the instantaneous power vs. time on a scope, then measure the peak-peak amplitude of the integral with statistics to get energy. In the pyro sensor case, I simply measure the amplitude with statistics. My Agilent MSO7054 scope can do this, but has some deficiencies: 1. It doesn't automatically compute relative standard deviation which is the important thing, so I have to type in the std.dev. / mean every time with my calculator to see the effect. Since the OPO average energy might change along with the std. deviation when a change is made, I can't just look at the absolute std. dev.. I need relative std. deviation. 2. It does accumulating rather than moving average stats., so I have to press "reset statistics" to start a new accumulation every time I make a change to the optics to see what the effect was. 3. Ideally I'd like a trend plot of the relative standard deviation as well. I've been considering three other scope models, the Agilent 9000 series, Tek DPO7000, and Tek MSO4000. Today I evaluated the Tek MSO4054 and Agilent 9000. The Tek can do a moving average statistic which is an improvement. But still no relative standard deviation. It doesn't allow one to write arbitrary expressions using the statistical measurements, only the built-in waveform measures, so there is no way to compute rel. std. dev. with its math expression feature. The Agilent 9000 (I forget precisely which model) also had no way to compute rel. std. dev., and I couldn't figure out whether it was doing moving ave. or accumulating stats. I didn't spend a whole lot of time with it after being sure it wasn't an improvement over the MSO4054. Tomorrow I will see a Tek DPO7000, but after studying the manual tonight, I'm convinced that it will also not be able to write math expressions using the stats. So I expect I will discover that it too can't do what I want. A pal at work recently bought a LeCroy 104MXi-A which costs less, has more BW, more memory, and faster sampling than the 500MHz Tek and Agilent scopes that are about the$ limit my boss can handle.

He told me it can basically do everything I want! I will call LeCroy
tomorrow and request a demo. They lent him one for 5 days to eval.

But many people swear "LeCroy sucks." Actually, I used one in college.
It had statistical calculations at a time when this was unheard of. It
made easy work of some physics research that we were doing on organic
photo-refractive polymers.

So while the LeCroy's might not be the best electronic debugging tools
(slower waveform update rate under some circumstances) for finding
glitches, etc., they do seem to be superior laboratory data acquisition
and analysis platforms, for a similar price class to Tek and Agilent.

I will hopefully discover the real truth in a few days.

You could look at the higher end Rhode & Shwartz and Yokogawa offerings
too.

shrtrnd

Jan 15, 2010
3,826
I repair test and measurement instruments.
Hewlett Packard lost a lot of expertise when they became Agilent.
Tektronix had a great reputation, but has been living off it's rep for a while now.
Most everybody I know has been breaking into the LeCroy's for the reasons you list.
Cheaper, and they're turning into go-getters in capability, trying to get market share.
My comment is that LeCroy gear works remarkably well when new.
However, they sell cheaper, because they're using cheaper parts in their assemblies.
As the LeCroy instrument ages, it is more prone to circuit drift, and they're pretty tight
about giving out circuit repair information (they prefer to do their repairs themselves).
I'm not an engineer, I'm a repair tech. You oughtta get a few good years out of their
product, but as the circuits age, you will experience drift in the readings because of the
I like to think as LeCroy actually makes a name for itself (trying to steal market share from Agilent and Tektronix), that they'll up the quality of their components, to make their innovative instruments a little more stable over time.

M

Mr.CRC

Jan 1, 1970
0
BobW said:
Mr.CRC said:
Hi:

I am trying to measure the shot-to-shot energy stability of a pulsed
optical parametric oscillator. 

We recently went through a similar exercise with Lecroy, Tek, and Agilent,
except our concern was high speed data (>10Gbps) and low jitter
measurements.

Lecroy has come a long way and is certainly the best bang for the buck if
you don't need super high sampling rate, very low jitter, and very low noise
floor.

The Agilent is the best for sampling rate, jitter, and noise floor, but you
pay for it. I was not too impressed with their user interface on their
DSA91304A.

The Tek is a happy midpoint for performance and price.

With either of these scopes, you can certainly write your own processing app
or purchase it if it's available.

for 3rd party apps.

Certainly the Windows based scopes can run auxiliary apps. The Agilent
90000 and Tek 70000 class scopes are about 5x my budget range. I could
just convince by boxx to let me buy a Tek DPO7000, if it were perfect.

But today revealed that it can't do this rel. std. dev. measurement out
of the box either. Tek support indicated that it could be done via an
application written to use its programming interface.

Good day!

M

Mr.CRC

Jan 1, 1970
0
Michael said:
Mr.CRC said:
Hi:

I am trying to measure the shot-to-shot energy stability of a pulsed
optical parametric oscillator.

I have a Lecroy 44Mxi which offers the facility of linking measured data
very directly to your own processing in MATLAB (or some other things)
running on the scope itself. I think the model you mention has the same
feature. I have had no problems with mine.

Michael Kellett

Thanks for the input.

MATLAB integration is interesting, and is also offered on Agilent 9000
series and probably higher models. LeCroy also seems to integrate
MathCAD. Too bad it's not Mathematica, which I know. I have MATLAB,
but haven't had time to work with it much. My company would be happy to
send me to a quick course on it if I wanted.

My co-worker get part way through a demo of the 104Mxi-A today, but I
had to run to a seminar with an interviewee.

I think it may be possible to do what I want with the LeCroy out of the
box, and even in more ways than one.

I have a borrowed Tek MSO4000 now, to evaluate whether to keep the one
in the unopened box.

My boss has the attitude that if the one we just received is generally
useful in our laboratories, then it might be easiest to just keep it,
and get something else later it necessary.

If I'm lucky I'll wind up with one of each of Agilent 7000B, Tek
MSO4000, and a LeCroy 104Mxi-A!

Good day!

M

Mr.CRC

Jan 1, 1970
0
John said:
Hi:

I am trying to measure the shot-to-shot energy stability of a pulsed
optical parametric oscillator.

Why not use the scope as an acquisition front-end and export waveforms
into a PC? That gives you a lot of cheap options for doing analysis.

John

John, this is certainly a workable approach. It would be preferable to
do it out of the box though. Also, if I can see a numeric value, as
well as a trend line, it would be peachy.

PC apps aren't my specialty, though I could figure it out given some
time. I prefer to program bare silicon. In that regard it might be
more fun and expedient for me to hack a gadget that combines a peak
detector with a micro to compute relative std. deviation, and spit it
out as an analog value to plot on a scope in strip chart mode, as well
as show on a meter.

This would be relatively easy to do with the rather slow pyroelectric
sensor signal.

We have a contractor programmer who does most of our data acquisition
software. He could possibly do it, but he's a bit overloaded these
days. As it seems are most of us who are still employed.

Perhaps I should also be looking into whether or not the laser power
meter readouts can produce this statistic (when in energy meter mode).
And if not, why not?

Good day!

M

Mr.CRC

Jan 1, 1970
0
Paul said:
With photodiodes, you can back-bias them, then feed the output into a
capacitor to ground, paralleled with a suitably high valued resistor,
and digitize the output with a high-impedance instrument. You no longer
need a fast instrument since the capacitor does the integrating. Size
the resistor so that the charge decays back to zero between pulses.

Paul Probert

Yes, that will give me a signal similar to what is produced by the
pyroelectric sensor.

Speed isn't the problem, lack of sophisticated built-in statistics is.

Good day!

joel_woodward

Nov 13, 2010
1
Agilent 9000 has a "UDF User-definable Function" applications. You can write your own analysis function in Matlab, and then the scope will import the .m file. You now have whatever math/statistics/analysis that you want integreted in the scope menu that runs in real-time. So, you no longer need to rely on the vendor to create the analysis/math/function....you now have access to any math/analysis/function that you want. The 9000 has a 60 day free trial of all applications including this one.

rickyrockrat

Dec 12, 2010
1
Lockup reboot....Did the signal not happen or did I lockup again

The most irritating thing about the LeCroys is Windows locking up. We had a high end one and I'll never forget the lockups on it. It was hard to tell if Windows had gone south (again) or the signal just never triggered.

I think anyone is nuts to build a piece of test equipment around windows. In another life, I programmed at the win32 level (painful, but compatible with all 32 bit versions of windows), and I know why it's so buggy.
Cheers.

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