2 Oscilloscope Questions...

Celtic Mech

Hello all,

Just picking some brains on these 2 questions (Hope they are transcribed correctly)...if anyone has any insight into the answers, please advise:

1) The trace of an oscilloscope begins when the input is at approx 10Volts but peak voltage indication is +/- 20 Volts. What can you do to begin the trace at zero volts?
a) adjust volts per division to 0v/cm
b) adjust the horizontal position to show the full trace on the screen
c) adjust the trigger level to zero volts trigger

2) How should an oscilloscope be set up to measure a 50millivolt ripple superimposed on the 24V DC output of a "115V AC, 400HZ Three Phase" Transformer rectifier?
a) select the channel to "DC" mode, select Volts per cm to "5Volts" and select the sweep time to 0.0025 seconds
b) select the channel to "AC" mode, select Volts per cm to "10Millivolts" and select the sweep time to 500 Microseconds
c) select the channel to "AC" mode, select Volts per cm to "50Millivolts" and select the sweep time to 400 Microseconds

FoxT

I am reluctant to write out a full answer - but here are some hints:

Q 1
A scope can operate in free run mode (ie it continuously updates the display) or triggered mode (ie it updates the display once whenever the input voltage exceeds a threshold specified by the trigger level.

Is the scope here triggered or free running? What would you do?


Q2
Here you have a 50mV Ac ripple superimposed on a DC signal. You want to measure the ripple. You must do two things:
- remove the DC component of the signal. (how?)
- then adjust the vertical resolution/gain so that the ripple occupies a couple of cm on the screen so you can measure it fairly accurately. (how?)


Cheers, FoxT

A320

Celtic Mech,Module 7 B2 i take it,those questions look familiar!!!!!!