PMZ-11 Help!

[Stef]

Hallo everybody,
First, excuse me for the language, but I am not from Poland.
But I'm in big need of a little support, to understand how to use correct
this appliance - Klerfaktormeter PMZ 11.
I have German and Polish manuals, but this languages doesn't work for me
So, my only hope is in you!
If someone is familiar with this PMZ, and have time and will, to help me to understand
some basic rules for work.
Thank you, before!

[Einherjer]

Hi, I have this piece of equipment, but Polish version. I'll try to write a short manual for you tomorrow. Could you add photo of front panel of your PMZ? I have no idea how switches and knobs are named in German version.

[Stef]

Thank You!!!
Don't worry about the pictures. I have all, and will show front panel later.
Also and schemes, if necessary.

But let me first introduce you in my problems with this appliance.
I got it from our stock at work, scrapped.
Of course, it didn't work.
When I hoked oscilloscope at the output, sine-wave was bad damaged. and frequency meter didn't work.
But I discovered the problem. It was a zener diode.

Now, when I try to measure, and push the right white button, the sine is much better, and frequency meter works.
But still, wave is not completely clean. There is a step at th top half. And changing frequency, the step moves to the top of sine.
My attention now is on WZ plate.

But, please, tell me first.
What should I see at the output?
Clean sine wave, or damaged because of distortions of measured appliance.
Now I measure just my wave generator.
When I calibrate, the sine wave is perfect.

[Stef]

Marry Xmas!

And one more thing to ad.
When press measure button, the amplitude of the sine decrease at the output, about 4 times.
But this is not all.
It decrease then slowly a little more.
If we watching the pointer, first it going to 0.25% and then slowly to 0.1%. to say.
Is this normal behavior?

[Einherjer]

Output is input signal after notch filter, that is distortion residual without base frequency. In ideal world if you connect distortion less generator to PMZ you should see nothing at output. Behaviour of your PMZ is normal, you see that notch filter is tuning. However, I'm not sure if it's properly calibrated --- sine wave should be attenuated much more. Before you press measure, you should adjust potentiometer on front board that pointer indicates 100%, do you do this? Do you know declared THD of your sine generator?

[Stef]

Fine!
Thanks.
I don't know the THD of this generator. It's some old American brand. Will check in the net.

I don't know what the manual says.
But try to calibrate my PMZ, as watch the pointer to rich the right side of the scale, or 0 db.
Right?

Let me, yet, post the shots of oscilloscope.
The first is when calibrate.
The second, when press measure.
The last, 15 sec. after pressing button.

And an English version, of front panel, of the PMZ-11, not mine.

[Einherjer]

But try to calibrate my PMZ, as watch the pointer to rich the right side of the scale, or 0 db.
Right?

Right. Then switch "distortion" to 100% and press measure. As the pointer rich left side of the scale change change distortion range to lower until it stabilises. It takes some time. If your sine generator have reasonable specifications reading should be below 0.1%

[Stef]

Well, now is coming the next question.
When we move down to -10, or to -50 Dbs,
must we again calibrate with the left potentiometer?
And, when pointer stabilizes, to say, with the -10, or -20 Db. pressed button, what the pointer shows?
The actual %-level of THD, or we must recalculate something ?

[ciasteczkowypotwor]

Hello,
Service manual, and user manual: http://bee.mif.pg.gda.pl/ciasteczkowypo ... 0mierniki/

[Einherjer]

Maybe I'll explain you how this kind of THD meter works. It has automatically tuned notch filter and AC voltmeter and input amplifier/attenuator. When you press "calibrate" voltmeter is directly connected to input amplifier. It measures "whole" signal, so this is your 100%, and that's why you must change range to 100% and adjust potentiometer that pointer indicates 1. After this you press "measure". Now voltmeter measures signal at the output of notch filter. Filter automatically tunes to base frequency and removes it from the signal --- residual is distortion. Now switching range buttons change just range of voltmeter, so you should not adjust left potentiometer. In the 100%, 10% 1% ranges read upper scale. For example if range is 10% and pointer indicates 0,6 it means 6%. If range is 30%, 3% or 0,3% use bottom scale, for example if range is 0,3% and pointer indicates 1 it means 0,1%.

[Stef]

Pretty clear. Very good explained. Thanks.
Now is time for real test measurements.
First I measured the sine-generator.
PMZ shows about 9 % THD.
This is too much, but because the generator is unknown device, lets accept it.
Next, I measured my DAC output, signal sours was laptop with Spectralab software.
Again very high THD, in neighborhood of 8%.
Sine wave, in measure position of the button, is very clear, but is not straight line, as should be.
Should be, because this DAC - Behringer SRC2496(moded), is measured, and has 0.00...% THD.
I show it down.
Why is so ?
May be, the notch doesn't remove completely the base frequency ?
On which PCB is the notch, if must to check it? And how?

[Einherjer]

I have same problem with my PMZ. Notch filter is not tuning completely. Unfortunately I don't have time to repair it and I haven't been searching how to do this yet.

[Stef]

Yes, but just if You are able to tell me which scheme in the manual is it, to take a look, and think.
What are that, so called Wien - bridges or so?
May be I must to translate and read this? : viewtopic.php?f=5&t=11202&hilit=pmz+11

[Stef]

I have same problem with my PMZ. Notch filter is not tuning completely. Unfortunately I don't have time to repair it and I haven't been searching how to do this yet.

May be win.
Tried some adjustments.
Try You, too. It's easy and fast.
After removing the side cover, I have access to the WZ-plate.
I use my laptop and DAC, like referent source -1Khz.
Connect the two scope-probes to the points 27/28 and 13, at the bottom of WZ.
Calibrate and push measure button. Watch the 2 sine-waves.
With trimer R24 on WZ try to equal them.
Next, replace one probe to the output of the PMZ device.
With the 2 screws on the "balck box" - box wit the 2 photo-resistors and a bulb, adjust the line on the scope screen, as close to the straight line, as possible. In the same time, check the pointer on the scale, to rich as close to the minimum, as possible.
If we accept the DAC has 0.00..% THD, the device is calibrated.
In my case, it shows just 0,04% THD, what is close to the reality.
The line on scope, is with 50mV amplitude, pressed -0,3% button PMZ-scale.

Next I measured my sine-generator.
Now it shows 2,4% THD.
I know, it is no good, but we have something interesting on the scope, hanged to the output.
Now I have some kind of saw wave, with small steps on it.
The frequency of the wave is 2K, not 1K as generator gives.
I think, now we see, the second harmonic-wave, and the higher order harmonics on it.

P.s. the 2 screws are very sensitive to touch and vibration. After adjustment, I fixed them with molten candle.