Oscilloscope input attenuation

[aland]

The input options on a Rigol (and many others I imagine) include an attenuation ranging from <<1 to >>1.
1x and 10x probes and their effects on impedance and why 10x (or higher) is necessary as frequency increases I understand.

But what is the attenuation doing? Is it also altering input impedance or just a gain or display scale beyond the input seen by the probe? The manual gives no clue so I presume it well know to those with greater experience of scope measurements.
 

[omgfire]

w2aew's video:

[aland]

So the attenuation only scales the volts/div numbers displayed on screen. The options ranging from x0.001 up to x1000 are mostly redundant and only the x10 useful if I only have a x10 probe.
Also changing this attenuation has no influence on the load the probe presents to the circuit.
Is that right?

Thanks

[w2aew]

So the attenuation only scales the volts/div numbers displayed on screen. The options ranging from x0.001 up to x1000 are mostly redundant and only the x10 useful if I only have a x10 probe.
Also changing this attenuation has no influence on the load the probe presents to the circuit.
Is that right?

Thanks

Correct - it only changes the numbers on the screen to be correct with a given probe.  The load presented to the circuit is entirely dependent on the probe being used.  Some higher speed scopes give you the ability to change the *scope's* input impedance between the standard 1Mohm and 50 ohm, but that's another subject.

[David Hess]

But what is the attenuation doing? Is it also altering input impedance or just a gain or display scale beyond the input seen by the probe? The manual gives no clue so I presume it well know to those with greater experience of scope measurements.

Usually oscilloscope attenuator alters just that, attenuation, without changing active gain or display scale.  The input impedance needs to remain constant or the probe compensation will be affected by oscilloscope attenuation changes.

It is difficult to alter active gain without changing transient response and bandwidth.  Old analog oscilloscopes which do this at their highest sensitivities usually lower their bandwidth either a little or a lot and require separate calibration.

DSOs and especially cheap DSOs may sacrifice ADC resolution to implement some vertical scale factors.  It annoys me when they lie about this in their specifications.  If you are throwing out bits and dynamic range at some attenuation settings, then your oscilloscope does not have the same resolution at all vertical input scale factors.  USB oscilloscopes are especially bad about this.

The old Tektronix 2440 DSO does this to get scale factors of 200 uV/div, 500 uV/div, and 1 mV/div from 2 mV/div but forces averaging mode so at least it is apparent when it happens and the documentation provides details.