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Rigol DG1022 Function Gen Frequency Counter Function
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xrunner:
I was playing with the frequency counter function of my Rigol DG1022.

The manual states:

"Counter with high accuracy and wide frequency band can measure frequency, period, duty cycle, positive pulse width and negative pulse width of the signal with the frequency from 100mHz to 200MHz (single channel)."

When I feed it a 10 MHz signal using my own external GPSDO, which outputs a 10 MHz signal to less than 1 Hz accuracy, the counter on the DG 1022 has on it's display (using it's internal reference):

9.99995 MHz

I read that as 50 Hz low

If I switch the DG1022 to an Ext. 10 MHz reference, it shows on the display:

10.0004 MHz

which I read as 400 Hz high.

I obtained the calibration manual for the DG1022 and performed the calibration for the internal and external frequency generation. The generator outputs 10 MHz to within 1 Hz, but the frequency counter yet still reads the same way. There is no specific calibration step for the frequency counter. As far as frequency is concerned, there are only the steps for the Frequency (Ext) Adjustment and Frequency (Int) Adjustment.

I am not sure what is going on with the DG1022 frequency counter. It makes little sense to me. It seems to me it should be as accurate as the frequency generation, but it isn't.

Anyone got any ideas on how to make sense of this?

xrunner:
This is interesting. I fed my DM3058E (which the manual states can measure up to 1 MHz) and my DG1022 (which the manual states can measure up to 200 MHz) both the same 1 MHz sine wave from a Marconi 2022. This 1 MHz signal is known to be accurate to better than 1 Hz using known accurate frequency counter locked to a GPSDO.

The DM3058E frequency counting function is closer than the DG1022's <-- a unit expressly dedicated to generating periodic waveforms!  :-//

For some strange reason, the frequency counter in the DG1022 is not as good as the one in their DMM. It generates accurate frequencies, but cannot count them as well.

This is fascinating to me. I'm going to contact Rigol and see what they have to say about it.  :wtf:

jpb:
I think there has been another recent thread on this. I also have a vague feeling this came up in conjunction with the Rigol D4000 series some time ago. There the issue seemed to be the fact that the counter was a very simple binary affair which gave rather odd gates and some rounding issues but I can't remember the details.

I had a quick look at the manual which doesn't seem to state gate times and so on. It gives the accuracy at 6 digits/sec. I think the generator's frequency counter function is less accurate because it is simply an add-on, I don't think it was designed in. The accuracy I would guess is +-2counts at best. Though the DACs clock frequency is quite high I suspect that it is scaled up and that the counter clock is lower.

It will be interesting to hear what Rigol say.
_Wim_:

--- Quote from: jpb on April 26, 2016, 06:16:22 pm ---I think there has been another recent thread on this.
--- End quote ---

Yes, see https://www.eevblog.com/forum/testgear/rigol-dg1022-frequency-counter-error-(to-a-lesser-extent-the-1054z-as-well)/msg868135/#msg868135
xrunner:
First - thanks to both of you for entering the thread. I did go back and read the thread you referred to. Mine acts the very same way with the exact same results. I have opened a ticket this morning on the Rigol NA website - let's see what they have to say about it. It certainly doesn't appear to be a "Counter with high accuracy ..." like stated in the manual.  :o

But ... here's another weird thing I noticed too. When I lock my Marconi 2022 RF generator to my external 10 MHz GPSDO and set it to output 10 MHz and look at both waveforms on my scope - the output never drifts in relation to the 10 mHz reference.

This is not what happens on the DG1022. If you watch it closely over a few minutes - the 10 MHz output from the DG1022 will drift over time in relation to the reference it's supposed to be locked to. I know it's using the ext reference because if I disconnect it, it gives a message and the output changes to it being very obviously a frequency multiple-Hz different than the reference. I'd like someone to try that themselves. I do not understand that at all.  :palm:
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