Keysight DSO/MSO 3000 Series: Neg. DC offset on Probe Compensation terminal ...

[_Harry_]

Hi!

That's my first digital scope: A MSOX3024T + brand new.

Sure - my finding is not a big deal - just kinda blemish ... but perhaps one experienced user knows a way to correct that ... (maybe using remote programming or somewhat)

Even when the scope runs on operating temp, that 2.5V / 1KHz square test signal on Probe Comp terminal has a negative DC offset of 100mV ... 120mV (verified using a second scope). Seems there is no menu option for correction.

Little down side: The scope provides training signals, coming out on the same terminal (and on a 2nd one) and all of them have that negativ offset too ...


Btw:

I'm wondering, that these generation of scopes has no option for "zeroing" any input offset drifting caused by operating/environment temp fluctuations (good old analog scopes are equipped with a pot for DC "Balancing", and some of you may remind yourself on Tek probes, having a GND-Ref push button to check that from time to time).

Anyway ... at most sensitive setting = 1mV/div and warm scope (>30 min) the 4 traces just off by <+/-100uV/CH (still on factory cal); guess, that's ok.


 

[HighVoltage]

Set your acquisition mode to "Average" and see what value are you getting then.
On my MSO-X2024A series I am getting -10mV offset and on my DSO-X3034A I am getting -5mV offset
Are you sure your offset is set to 0.00 V in the Wave Gen setting?

[_Harry_]

Yepp, no offset is set for the BNC Gen Out, but settings for the "BNC" do not take any effect to the separate Probe Comp "lug".

Ok, using Averaging (# = 8 ), the Pobe Comp terminal Offset is only -70 ... -80mV. Maybe still a bit much?

On the BNC Gen Out it looks good. I've set the Generator signal equal to 1KHz with H-Lev. = 2.500V, L-Lev = 0.0V, High-Z -> these are the measurement results of the low signal on

• Aquire = Normal / high-Z out: -50 ... -70mV (that's caused by the probe; w/o the probe connectet the trace on screen is -5mV)
• Aquire = Averaging (# = 8 ) / high-Z out: -26 ... -28mV (dto. -> -2,4mV)

[HighVoltage]

Set the output impedance of the signal generator to 50 Ohm and do the same for input impedance of the channel that you do the probing with and connect both  with a 50 Ohm BNC to BNC cable. What is the offset then?
 

[_Harry_]

If 50 Ohm is set on BNC GEN out and CH1 / using RG-58 coax:

• -21 ... -23mV (-11 ... -13mV on open input CH1, so cable removed)

Unfortunately the Probe Comp terminal / Training signals on that can't be set at 50 Ohm ...

The generator signals on BNC Gen output look ok to me.
Just signals on Probe Comp terminal are not perfect (still -70mV ... -80mV on Averaging mode); maybe that offset can be corrected by SW ...