Rigol DS1052E measuring voltage incorrectly? - Page 1
Forum section: electronics / general

author: n3wbie
author_rank: Contributor
timestamp: February 08, 2012, 11:45:25 pm
content: I just received my Rigol DS1052E in the mail today (yay!) and hooked it up to a few batteries just for fun. It seems like it's measuring voltage incorrectly. Here's a picture of the scope alongside my multimeter:Hopefully you can read that the scope is measuring less than half a volt (360mV), while the multimeter is measuring almost three volts. After seeing this I ran the self calibration and afterwords it was measuring Vmax as 320mV.I'm hoping that I'm just making some stupid mistake. Is that the case?

author: IanB
author_rank: Super Contributor
timestamp: February 08, 2012, 11:50:46 pm
content: Most likely operator error.Do you have the probe on DC coupling? Do you have the probe attenuation set to match the probe?

author: amspire
author_rank: Super Contributor
timestamp: February 08, 2012, 11:57:27 pm
content: You must have the x10 probe plugged in, so you have the error of the scope and the probe combined.But also you have a lot of noise - 1.2Volts peak to peak of noise and an error of 0.2 volts, so all the error could be due to the nature of the noise.Try a clean voltage source like a battery before you start worrying. It should turn out to be fine.Richard.

author: n3wbie
author_rank: Contributor
timestamp: February 09, 2012, 12:09:40 am
content: Aha! I went to the channel settings and change the probe attenuation to 10X and it's working correctly now. Thanks! Should I keep it at 10x, or change it to 1x? I really have no clue what these settings doVpp is now 240mV, though, and it's connected directly to a couple of batteries. Is that normal?

author: Unknown
author_rank: Unknown
timestamp: February 09, 2012, 12:16:18 am
content: You generally want to keep the probe on 10x, unless you're measuring low level signals. Bandwidth and circuit loading is much better at 10x. Always match the scope's attenuation setting (which is just a scaling multiplier, 10x multiplies all indicated voltages by 10) to the probe, otherwise you will get confused.The noise sounds high, weren't there some earlier threads about some of these scopes with high noise? I don't remember the exact symptoms and conclusions. Batteries should be very quiet. Can you post a screen shot of the noise? The noise on the picture you showed looks like just 1-bit quantization noise to me.

author: IanB
author_rank: Super Contributor
timestamp: February 09, 2012, 01:00:31 am
content: The Rigol does an excellent job of picking up ambient noise. Especially if you put your hands anywhere near the probe tip or ground wire when making a measurement.

author: n3wbie
author_rank: Contributor
timestamp: February 09, 2012, 01:08:59 am
content: Sorry for not replying sooner. I've been struggling to get the oscilloscope to connect to my PC and just now got it working. What settings should I use when taking a picture of the noise for you?Thanks

author: IanB
author_rank: Super Contributor
timestamp: February 09, 2012, 01:11:15 am
content: When I get home from work in a little while I will capture a measurement of a 1.5 V battery for you to use as a comparison and will explain what settings I used.

author: n3wbie
author_rank: Contributor
timestamp: February 09, 2012, 01:21:22 am
content: OK, wait a minute.. I connected the scope directly to a 1.5V battery (it was connected to a battery holder) and this is the result:Is Vpp = 8mV is a fairly low noise level? I wonder if there might be a bad connection somewhere in the battery holder.Thanks for all of your help!

author: amspire
author_rank: Super Contributor
timestamp: February 09, 2012, 01:56:44 am
content: 8mV p-p is not bad. It probable means you are still getting something like +2 bits to -3 bits of noise in the 8 bit A/D. A DS1052E can usually do a little better then that, but it might be something to do with the connection to the battery. The best that would probably be possible is +/- 1 bits of noise, so it is not far off perfect.Richard.

author: IanB
author_rank: Super Contributor
timestamp: February 09, 2012, 02:15:47 am
content: OK, it seems like you have it sorted, but for reference, here is what I obtained.This is a raw measurement with the probe set at x1:Note the B next to the 200 mV label indicates that the bandpass filter was turned on in the channel menu to remove high frequency content.Then this is the same measurement with a 100 Hz digital low pass filter applied to remove the noise (this filter would be way too aggressive with a moving signal but it's OK here to check the DC measurement):Then with the digital filter turned off, but with 16 sample averaging in the acquisition menu:Lastly, a picture of the probe setup:The battery under test measured 1.347 V on my meter.

author: n3wbie
author_rank: Contributor
timestamp: February 09, 2012, 01:02:44 pm
content: Thanks for all of your help!

author: sacherjj
author_rank: Frequent Contributor
timestamp: February 09, 2012, 02:19:23 pm
content: Never really thought about using little magnets for something like that. Great idea.

author: robrenz
author_rank: Super Contributor
timestamp: February 09, 2012, 02:23:02 pm
content: Magnets! I wondered what was holding thos tabs on

author: n3wbie
author_rank: Contributor
timestamp: February 11, 2012, 08:39:41 pm
content: Since it's the weekend I've had a bit of time to mess around with this and have a question. I have the scope connected to a 1.5V battery again, just like before, and with a setting of 1V/div I get this:With a setting of 200mV/div I get this:Why is Vpp so different when I change the vertical sensitivity?

author: IanB
author_rank: Super Contributor
timestamp: February 11, 2012, 09:45:35 pm
content: The oscilloscope has a precision on the vertical axis of 1/200 full scale.In the first case, 1 V/div = 8 V full scale. Dividing 8 V by 200 gives 40 mV per pixel. The scope is measuring three pixels of noise giving 120 mV.In the second case you have 8 x 200 mV = 1600 mV full scale and 1600/8 = 8 mV per pixel. In this instance the scope is measuring four pixels of noise giving 32 mV.In both cases you are measuring various sources of signal, sampling and quantization noise. The Vpp measurement is not actually "real" in any true sense. For the Vpp measurement to be useful you need to apply it to a strong well defined signal trace that fills most of the vertical plot space so that the signal to noise ratio is small.