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JohnBee

Can the Discovery 2 be calibrated?

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I noticed the wave shape with our Discovery is slightly deformed(on the edges) and wondered if there was a way to trim or calibrate this with the unit itself?

I tried with different leads(rated for 150Mhz) and compared to another scope, and found the signal distortion was consistent.at lower frequencies(>1Khz). 

 

JohnB

Edited by JohnBee

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Can you post a picture of what you are describing?  You description suggests that the device might be clipping, and looking at a picture of the waveform would help to diagnose it.

Dan

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It appears as though my unit cannot be calibrated (error) on voltage. 
I tried calibrating it several times to try and get it to display wave-forms properly, but the calibration fails on the second portion of the scope as a result of the offset being to far out of spec. 

Given the rash or issues I've been having with this unit since we received it, I'm beginning to think it's malfunctioning and should be returned for further inspection.
Needless to say, I can't help but feel as though we've gone in the wrong direction with this purchasing instead of getting a physical scope. :/

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Hi JohnBee,

What edition of Waveforms 2015 do you have? I know for editions 3.3.3 and earlier there was a known problem with the calibration where it would fail as you described, but I believe in the most recent edition (3.3.5) this issue was corrected, although I have not gotten to opportunity to confirm this for myself.

Thanks,
JColvin

Edited by JColvin

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Hi JColvin,

I'm currently using v3.3.5. Though I think I may have made headway in that it appears as though my issues may be due in-part with the BNC adapter module. And so I'm going to run a few more tests this evening in hopes of pin-pointing the issue. 
 

 

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Success, I was able to calibrate the unit without the BNC module attached to it. Though when I attach it, I cannot calibrate it(error). 
Does this mean the module is defective or is this a normal consequence to having the module attached?

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Hello,

The calibration should work with the BNC adapter too, just make sure to have on Scope DC coupling and 1X probe, and 0 Ohm for AWG.

On Analog Discovery (1&2) the Scope input compensation can be adjusted using the 4 trimmers on the board. Using the wire kit the process looks like this:
Using square waveform of 2-5kHz, 2V amplitude, select auto synchronization, and in scope have 20-100us/div, 500mV/div range, trigger on Wavegen 1.

1. Connect the W1 to Scope 1+ and 2+, connect 1- and 2- to ground.
Adjust 2nd (1+) and 3rd (2+) trimmers to have a good square wave.
C1 right and C2 overcompensated:i1.png

2. Connect the W1 to 1+, 1-, 2+ and 2-, and reduce ranges.
Adjust 1st (1-) and 4th (2-) trimmers to have straight line.
C1 right and C2 overcompensated:i2.png

On the BNC adapter the 1- and 2- are tied to ground. 
The probe 10X compensation can be adjusted with the probe trimmer based on a 1-2kHz square wave, see: 

 

The Network Analyzer can also be used for tuning. With this you can see the resulting spectral characteristics.

a. Single ended adjustment for Scope channel 1
Connect 1+ to AWG1 and 1- to GND, tune the 2nd trimmer.
Yellow tuned and red untuned.
image.png.ef43c6d0cf26bd97776cd3aaac9ee926.png

b. Differential adjustment for Scope channel 1.
Connect 1+ and 1- to AWG1, tune the 1st trimmer:
image.png.4f053bd492d49c7d5a93e3931c731f7e.png

To tune Scope channel 2:
c. Connect 2+ to AWG1 and 2- to GND, tune the 3rd trimmer.
d. Connect 2+ and 2- to AWG1, tune the 4th trimmer

Edited by attila

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7 hours ago, attila said:

Hello,

The calibration should work with the BNC adapter too, just make sure to have on Scope DC coupling and 1X probe, and 0 Ohm for AWG.

On Analog Discovery (1&2) the Scope input compensation can be adjusted using the 4 trimmers on the board. Using the wire kit the process looks like this:
Using square waveform of 2-5kHz, 2V amplitude, select auto synchronization, and in scope have 20-100us/div, 500mV/div range, trigger on Wavegen 1.

1. Connect the W1 to Scope 1+ and 2+, connect 1- and 2- to ground.
Adjust 2nd (1+) and 3rd (2+) trimmers to have a good square wave.
C1 right and C2 overcompensated:

2. Connect the W1 to 1+, 1-, 2+ and 2-, and reduce ranges.
Adjust 1st (1-) and 4th (2-) trimmers to have straight line.
C1 right and C2 overcompensated:

On the BNC adapter the 1- and 2- are tied to ground. 
The probe 10X compensation can be adjusted with the probe trimmer based on a 1-2kHz square wave.

Awesome info yet again!
I'll give it a try just as soon as I get in today. - Fingers crossed 

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The devices are calibrated during the build test.
Recalibration is only needed in case it gets altered by time... but there are no components on the device that could weaken... or you want even better precision.

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Okay so I had another go at it and found the same error;

 

Check the connections!!
The measured voltage on Oscilloscope Channel 1 is between: 2.244575 V and 2.245164 V
But it should be around: 5 V

It might be that the Arbitrary Waveform Generator 1 Offset is not calibrated correctly.

 

That said, are the break-out leads on the BNC modules working in the same way as they would be directly from the unit? 

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The AWG1 got wrongly calibrated or the Scope 1+ and 2+ are not connected to AWG1

No. On the BNC module the Scope and AWG signals are not connected. These are marker with NC.

I would recommend to the Load Factory calibration and use the device with this.

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NC = No Connectivity?

As it turns out, this was my issue all along. As I was trying to use the leads(ether Waveform Gen(1,2) and the Oscilloscope(P,N) to calibrate with.
To which I'd add, I did not see the pin-out assignment changes in the BNC documentation :/

That said, I'm happy to report that the unit is now calibrated and the waves and behavior looks much better than it did before.  
Too bad it took this long to figure out the problem though. 

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On 6/28/2016 at 2:09 PM, JohnBee said:

Check the connections!!
The measured voltage on Oscilloscope Channel 1 is between: 2.244575 V and 2.245164 V
But it should be around: 5 V

attila, I have the same problem as JohnBee (above) but I've calibrated AWG1 several times and have made sure that 1+ and 2+ are both connected to AWG1 (with 1- and 2- both connected to ground). I can calibrate every other part of the AD2 except the scope. Any ideas what could be preventing me from doing that?

I'm using an AD2 with Waveforms 3.8.2 on Linux.

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Hi @nathancharlesjones

Make sure in the first step of the oscilloscope calibration you connect 1+/2+ to ground and only for the second step connect the 1+/2+ to AWG 1.

Please provide more detail about the failure, like screenshot with the measurements listed in the lower textbox of the wizard. 

image.png.9541d0c553f9674e67fe65149c4fb443.png

 

With WaveForms beta you can also perform quick offset calibration in the oscilloscope.
https://forum.digilentinc.com/topic/8908-waveforms-beta-download/

image.png.6a46b6bc4d3160bfdf0ebfbb093527f5.png

 

image.png.01607ab6816831a33eb9c8f69d6c917a.png

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