I have a question regarding an oscilloscope setting.
I have a 15V test point.
I am using the Tektronix TDS3014B.
When I clicked on the AUTOSET button.
I am getting 0V.

When I plug in the DMM to the test point. I am seeing 15V.
I was told that my setting for the probe should be 1M ohm and not 50 ohm set by the oscillascope when I click on autoset. Can someone explain to me why does it work that way (formula and calculations)? I learn better when I see numbers.
Thanks

 

Post a schematic of the circuit so we can see what you're measuring.

Are you using a scope probe?

My guess is that you're not using a probe and when you set your scope to 50 ohms input impedance it's loading the circuit.

Relevant portions of your images:

 

I am using a scope probe

 

Don't use AUTO SET button.

 

Are you using AC or DC coupling on the vertical input? If you want to use the scope to measure a DC level you want to use DC coupling on the vertical input channel.

If using a probe be it X1 or X10 unless it is a Tek probe do not use Autoset just select a 1 Meg Ohm input impedance.

Typically your source will be a low impedance. When you select a 50 Ohm input for a source which is high impedance and not designed to work into 50 Ohms you will load it. For example if I have a 50 Ohm source and select 50 Ohms input impedance I have what amounts to a 2:1 voltage divider and the scope will read about 1/2 of the actual input.

A Google of 1X 10X Scope Probes will bring up some drawings. A 1X probe is a straight shot while a 10X probe places 9 Meg Ohm in series with the vertical input. Along with the 1 Meg Ohm of the scope this makes for a 10:1 divider.

Ron

 

Thank you Ron for the detailed explanation. That helps!