Elenco 30MHz Dual Trace - Manual (Page 51)

Application
OSCILLOSCOPE INSTRUCTION MANUAL
48
DC VOLTAGE MEASUREMENTS
(Refer to Fig.7)
The following technique may be used to measure the instantaneous de level at any
portion of a waveform, or to measure a dc voltage where no waveform is present.
1. Connect the signal to be measured to the input jack and set the CH 1/ CH 2 switch
to the channel to be used. Set the COLTS/DIV and sweep TIME/DIV controls to
obtain a normal display of the waveform to be measured. The VARIABLE control
must be set to CAL.
2. Set the COUPLE switch to AUTO and the AC-GND-DC switch to GND. This
establishes a trace at the zero volt reference. Using the POSITION control, adjust
the trace to the desired reference level position, making sure not to disturb this
setting once made.
3. Set the AC-GND-DC switch to DC to observe the waveform, including its dc
component. If an inappropriate reference level position was selected in set 2 or an
inappropriate VOLTS/DIV setting was made, the waveform may not be visible at
this point (deflected completely off the screen). This is especially true when the dc
component is large with respect to the waveform amplitude. If so, reset the
VOLTS/DIV control and repeat steps 2 and 3 until the waveform and the zero
reference are both on the screen.
4. Use the X POSITION control to bring the portion of the waveform to be measured
to the center vertical graduation line of the graticule scale.
5. Measure the vertical distance from the zero reference level to the point to be
measured (at least 3 divisions desirable for best accuracy). The reference level
can be rechecked by momentarily returning the AC-GND DC switch to GND.
6. Multiply the distance measured above by the VOLTS/DIV setting and the probe
attenuation ratio as well. Voltages above the reference level are positive and
voltages below the reference level are negative.
The measurement is summarized by the following equation:
DC level + Vert div x VOLTS/DIV x Probe
For the example shown in Fig.7, the point being measured is 3.8 divisions from the
reference level (ground potential). If the VOLTS/DIV control is set to 0.2 V and a
10:1 probe is used, the dc voltage level is calculated as follows:
DC level = 3.8 (div) x 0.2 (V/div) x 10 = 7.6V