Oscilliscope Restistance

[eat411]

I need to know if the resistance in an oscilliscope is high or not. i
believe they have a low resistance, but i am not sure why they would
need to be designed this way. I would appericiate an explanation.

thanks in advance

 

[Lewin A.R.W. Edwards]

I need to know if the resistance in an oscilliscope is high or not. i
believe they have a low resistance, but i am not sure why they would
need to be designed this way. I would appericiate an explanation.

They should have a high input impedance. You want to load the signal
under test as little as possible => you want as little current as
possible to flow through the scope.

 

[Mantra]

eat411@subdimension.com (eat411) wrote in message news:<f412937d.0410052217.21aba394@posting.google.com>...

I need to know if the resistance in an oscilliscope is high or not. i
believe they have a low resistance, but i am not sure why they would
need to be designed this way. I would appericiate an explanation.

thanks in advance

Now that you've gotten mutually exclusive and contradictory answers,
here's the real answer.

It depends on your frequency of interest. If you can assume a lumped
equivalent model applies (generally under ~500 MHz) then you want your
probe top to look like a high impedance (i.e. invisible) to the
circuit under test. If you can *not* assume a lumped equivalent model
applies, then transmission line effects are important and you want to
assure an impedance match to avoid introducing reflections into your
scope circuitry or your circuit under test so you'll want the probe
tip to look like the charactistic impedance (typically 50 ohms) (i.e.
invisible). In other words: "yes".

MM