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Camarillo

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    Why does the amplitude at low frequencies drops in the Analog Discovery 2?

    in Test and Measurement

    Posted · Edited by Camarillo

    Hi, just got back from the lab and I think i don´t understand this that well......

     

    This is the actual 100uS signal that I want to measure. Please note that the amplitude is 20 mV/div.

    The signal should be around 55 or 57 mV.

    The frequency of such signal is 25 Hz (with a pulse width of 100uS).

    299029869_SignalImage1.thumb.png.eb38ec636e202b3ea19d1e028baa7c07.png

     

     

    This is a closer look at the signal.

    Please note the change in the peak values. The normal signal hovers around 60 mV, and now the AD2 shows peaks of 100 mV. Still, the width is still around 100uS and the plateau is near that 60 mV value.

    739327105_SignalImage2.thumb.png.ffdc7ca447e2f52c9a96c07c084270f7.png

     

    If I try to measure the signal for a longer time, the voltage is not what is suppose to be. Please note the value drop to about 10 mV instead of the 60 mV.

    This is the same 100uS width at around 60 mV pulse as the first image.

     

    1211867536_SignalImage3.thumb.png.6853415065ac4360f680a086e521c989.png

     

     

    The actual signal that I want to measure is 10 seconds long (looks like the next one). Since I want to incorporate the AD2 in LabVIEW with another sensor, I first want to know if the AD2 can measure the actual voltaje. 

    315751346_SignalImage4.thumb.png.7fa907ea2b5414990823f7c04a875bf4.png

     

    Maybe my measuring skills are wrong and I need to go back to school.

     

    Can you provide some insight @attilain this regard?

     

    Thanks a lot.

     

     

     

    PS:

    I found this post but still can´t get the grasp on the concept:

     

    Why does the amplitude at low frequencies drops in the Analog Discovery 2?

    in Test and Measurement

    Posted

    Hello.

     

    First some context:

    I´m doing a measurement of a signal that has a 10 second period. It is comprised of several 100 us signals, all in that period. Such signal has a maximum 50 mV amplitude.

     

    This might be a very basic question but I´ll ask it anyway:

    If I zoom in to the 100us signal, I can see the correct amplitude.

    If I zoom out such as to capture the 10 second period, the amplitude decreases drastically (about 75% of the original value).

     

    Is there something that I´m doing wrong?

     

     

    Thanks in advance.

    I think it's broken

    in Test and Measurement

    Posted

    Two more things:

     

    1. I will now just measure +-40 volts. Can I use the differential measurement for that (Channel 1 and 2).
    2. Will try to revive the waveform generator in the near future.

     

    I think #1 is a given since here:

     

     

    and here:

    https://reference.digilentinc.com/test-and-measurement/analog-discovery-2/reference-manual?redirect=1#scope_input_divider_and_gain_selection

     

    states that the maximum input can be +-50 volts using differential measurement.

     

     

    Thanks in advance... and sorry for the super late reply.

     

     

    I think it's broken

    in Test and Measurement

    Posted

    On 2/19/2020 at 12:38 AM, attila said:

    Hi @Camarillo

    Probably some high voltage transient input or accidentally having the probe at 1x with high voltage damaged the ADG612.

    It appears I can´t post more pictures. I can´t delete the ones in the post above (don´t know how).

     

    Well, just to your point, it probably was that faulty switch that caused all of this.

    I think it's broken

    in Test and Measurement

    Posted

    Hello again. Almost a year and a half later.

     

    After reparing the oscilloscope (with your help, of course), I did use it for some other low level measurements and the digital side as well.

     

    Had to do some other measurements and was surprised by something:

    On 2/19/2020 at 12:38 AM, attila said:

    Hi @Camarillo

    Probably some high voltage transient input or accidentally having the probe at 1x with high voltage damaged the ADG612.

     

    One of my probes has a faulty switch for the x1 and x10 range. I started using a bench oscilloscope and that is where i found out.

    This is odd since they were bought with the BNC PCB for the AD2.

     

     

     

     

    IMG_20210804_130312550.jpg

    IMG_20210804_130317163.jpg

    IMG_20210804_130321058.jpg

    I think it's broken

    in Test and Measurement

    Posted

    Hi again......

     

    I think I broke it for sure now.

     

     

    This image is with the wave generator #1 with its output at 5 volts with no offset.

    image.thumb.png.c24917eff8826b7a3413d590f3bf2994.png

     

     

     

    After resoldering the ADG612, Channel two was able to mirror the information in channel one.

    image.thumb.png.29e523d33dcd2d8e2ffd2a7efd02da6a.png

     

     

     

    Here are both channels at the same time.

    image.thumb.png.313d71c3562581754677ab2efa994da9.png

     

     

     

    It´s strange because Channel one was not failing. Maybe it´s because my soldering skills with SMD is not that good. I just soldered the IC.

    Maybe I broke it for sure now.

     

     

    Did a device calibration setup and the first  two steps generate -5.05 volts. (it says demo mode but the measurements were made before disconnecting the device)

    image.thumb.png.ac53cb08fc6359dff374e08720beaa5e.png

     

     

     

    Right now I don´t have access to my AD1. Next week I´ll have access to it and will use it as a reference to measure analog signals.

     

    Can you provide some insight?

     

     

    Thanks.

     

     

    I think it's broken

    in Test and Measurement

    Posted

    On 2/27/2020 at 1:30 AM, attila said:

    Hi @Camarillo

    It is most probably the C2 ADG612 damaged, the first IC in the input path. 

    Hello. 

    Thanks for the info. 

     

    Just one question, and this might be very transparent for everyone but me:

    Which of the two ADG612 is the channel 2?

     

    I have all the intention to do that repair in this week. Good thing I have the AD1 for testing. 

    I think it's broken

    in Test and Measurement

    Posted · Edited by Camarillo
    Deleted the same image. Uploaded it twice.

    Thanks for the reply.

     

    Did the factory reset but the measurementes were the same. Although something happended that I did not notice: if I start channel 2 with the 500mV/Div, if i change it to 5V/Div, the signal from channel 2 goes to -3V and after a few seconds, it goes to +21 (with nothing conected to the probes).

     

    Did a calibration after loading the factory data. The waveform channel, both 1 and 2 passed. But the oscilloscope did not, and it showed the behaviour described above (-2.7 volts to +21 volts.

     

    Do you think it might be the MUX ADG612?

     

    Thanks.

     

     

     

    image.png

    I think it's broken

    in Test and Measurement

    Posted · Edited by Camarillo
    Definded the voltages.

    On 2/20/2020 at 1:47 AM, attila said:

    Hi @Camarillo

    I meant measuring the VOFF_SC2 relative to the device GND with external DMM.
    Having the scope channel 2 range 500mV/div or lower, changing the offset between -2.5V and 2.5V should change the VOFF_SC2 between ~1V and ~3V
    Above 500mV/div for offset between -25V and +25V change VOFF between ~1V and ~3V.

    Oh.... sorry, did not understad that.

     

    Did the measurements. They are within range:

    VREF2V = 0V

    VOFF_SC2 with 0V offset = 1.94V,

    VOFF_SC2 with 2.5V offset = 2.99V

    VOFF_SC2 with -2.5V offset = 1.01V

     

    All measurementes respecto to the device´s ground and with 500mV/Div for channel 2.

    I think it's broken

    in Test and Measurement

    Posted

    I´m sorry with all those uploads. Don´t know what I did but apparently I uploaded all the files again.

     

     

    The last two measurements:

     

     

    This one is the +2.5 Offset at VOFF.  I had to modify the range from 0.5 to 1 volt/div.  It measures 2 volts.

    2018914504_VOFFwith2_5voffset.thumb.png.6037e7c5d80eb236d52b49038c30c1cd.png

     

     

     

    This one is the NET409_1 with +2.5 volts offset.  I left the same 1 volt/div as the other one. It measures 0.5959 volts.

    1466025298_NETC409_1with2_5voffset.thumb.png.cf8c0fdc88777fe93b0557a840b13ce4.png

     

     

     

    What do you think?  Could the MUX be the problem?

     

     

    Thank you so very much.

    I think it's broken

    in Test and Measurement

    Posted

    Hello Mr Attila.

     

    I think I did the measurements but not sure if I did them in the right manner.

     

    My setup:

    -OSC1  ---->  GND

    +OSC1 ----> to test points

     

    Did all measurements with respect to GND of the AD2. In the last measurement I remembered that it also could have been differential measurements.  Did all the differential measurements and the result is the same with the other two with respect to GND of the AD2.

     

    I had to modify the +2.5 offset with 0.5 scale because the measurement will not show it self (higher than 0 volts I guess).

     

     

     

    This was the VREF_SC2, with respect to GND it was close to 2 volts.
    This was the VREF_SC2, with respect to GND it was close to 2 volts.

     

     

     

    This one is the NETC410_1 with respect to GND. It was 1.1947v

    This one is the NETC410_1 with respect to GND. It was 1.1947v

     

     

     

    This one is the diferential measurement, just took it after I´ve finished...

    Differential measurement

     

     

     

    This one is the VOFF with 0 volts offset. It was almost 2 volts (1.9969)

     1293762275_VOFFwith0voffset.thumb.png.635f90e4910090433fa6bfe4f3f5a3fe.png

     

     

     

    This one is NET409_1 with 0 volts Offset respect to GND. It was 0.5855 volts.

    1288373568_NETC409_1with0voffset.thumb.png.e7d38142b4e931f3e8cac3e34e0965e7.png

     

     

     

     

    This one is VOFF with -2.5 volts offset and 0.5 volts/div.   It measures 1.99 volts.

    1774759781_VOFFwith-2_5voffset.thumb.png.c1ab770d40ae142210ef37ddcc08491c.png

     

     

     

     

     

    This one is NETC409_1 with -2.5 volts offset with 0.5 volts/div.   It measures 0.5786 volts.

    711512169_NETC409_1with-2_5voffset.thumb.png.ac0db5de5baed8ba2cf495652a143de6.png

     

     

     

     

     

     

    VREF_SC2.png

    NETC410_1.png

    VREF_SC2 and NET410_1 Differential.png

    VOFF with 0v offset.png

    NETC409_1 with 0v offset.png

    VOFF with -2_5v offset.png

    I think it's broken

    in Test and Measurement

    Posted · Edited by Camarillo
    There. Had to convert the image to PDF for it to be uploaded.

    Hello.

     

    Mr Attila AKA "Technical Forum Moderator".

     

    I think i have the same problem as Mr Russell.

     

    My AD2 will not go down from +20 volts. I was doing some measurements with a transformer and the BNC kit for the AD2 and after some measurements, it looks like I also broke my Channel 2 input. The probes were x10 in the attenuation department.

     

    Will the solution suggested work also for me?     I have almost the same issue but  is not -21, is +21.

     

    The device works well measuring frequencies, the attached image shows the generator connected to channel 2, measuring 10 MHz.

     

    Discovery BNC.jpg

    Scope and WFG 10 MHz.pdf

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