LCR Meter Problem with Second Input offset adjustment

[BenjaminKe]

Hi Jean-Jacques,

On TP2 I measure a nice sinus with the correct frequencies and also the correct voltage (2.7Vpp).

But on TP1 I measure a nice sinus with the correct frequencies (100Hz, 1kHz, 10kHz) with strange voltages:
100Hz: 1Vpp
1kHz: 2Vpp
10kHz: 300mVpp

I guess the "Overflow" message which I get means that the 2Vpp are too high.

U20 Pin 14:
100Hz - sinus 2.8Vpp - ok
1kHz - sinus 5Vpp - NOT OK
10kHz - DC 1.5V - ok

U20 Pin 1:
100Hz - sinus 2.8Vpp - ok
1kHz - sinus 3Vpp - OK?
10kHz - sinus 800mVpp - OK?

It looks like I have a problem somehow with my filters here.

Best Regards
Benjamin

[snoopy_94]

Hi Benjamin,

It looks like I have a problem somehow with my filters here.

Yes!
More measures:
U20 pin 7 - LPF 11kHz, output of the first stage:
100Hz - sinusoïdal voltage (with offset of about -1.5V) --> 2.7Vpp
1kHz - sinusoïdal voltage (with offset of about -1.5V) --> 2.7Vpp
10kHz - sinusoïdal voltage (with offset of about -1.5V) --> 1.5Vpp

U20 pin 8 - LPF 1.1kHz, output of the first stage:
100Hz - sinusoïdal voltage (with offset of about -1.5V) --> 2.7Vpp
1kHz - sinusoïdal voltage (with offset of about -1.5V) --> 1.5Vpp
10kHz - DC about -1.5V

Verify the value of the resistances and capacitors!

Best Regards,
Jean-Jacques

[BenjaminKe]

Hi Jean-Jacques

First measurements:

Pin 7:
100Hz: 2.7Vpp
1kHz: 2.9Vpp
10kHz: 500mVpp

Pin 8:
100Hz: 2.7Vpp
1kHz: 2.9Vpp
10kHz: 500mVpp

I found the problem:
It looks like I had some wrong values for C57 and C5.

Now the trim passed

I have redone and finished also all other calibrations now and everything seems to work find.

Thank you so much!

Best Regards
Benjamin