Changing the Time Base
- When a signal is viewed on the CRO display the
period of the signal can be measured by counting the
number of horizontal divisions that the signal
"covers" on the display
and multiplying by the scale of each division.
- i.e if the signal
"covers" 4 divisions at 5
milliseconds per division,
the signal period is 20 milliseconds and
the frequency is 50Hz.
- Now because the signal being viewed can be a
large range of frequencies we need to adjust the viewing
scale on the display in order to achieve the optimum
viewing size of the signal.
- i.e if we attempted to view a
10Hz sine wave and a 10kHz sine wave on
the same scale one or both of the signals
would not be properly visible on the
A graphical example of
How Do We Change The Time Base?
- Well firstly
we consider the diagram below which shows the Time
Base Control labelled with Sweep
- Now we can see that the control has settings
labelled from 0.2 uS
per division to 0.2 S
- The time base is changed by simply rotating the
control to the desired setting. Some graphical
examples of this.
Things To Remember About The Time
- If we are viewing two signals on the display,
they cannot be viewed such that each signal is on a
different horizontal scale. So be aware of the setting of
the Time Base.
- The red knob ( the Variable
Time Base Control ) that lies within
the Time Base Control
must be rotated completely clockwise until a
"click" is heard to ensure calibration and
correct readings. (Be Warned -
there will be turkeys who play around with these knobs
just to ruin your results and get a laugh, so always be
sure to check this. )
Variable Time Base Control
- This control as mentioned above is located in the
centre of the Time Base
Control and is used to vary the
horizontal scale ouside the limits of the Time Base
Control. It is most useful to check the general shape of
- ALWAYS be sure that this
control is not left in the uncalibrated ( calibration
relies on the knob being rotated completely clockwise
until a "click" is heard ) position when making
measurements of signal amplitude.
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Revised: 15 September 2004