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XScopes
User’s Manual
DS-XScopes-3.5
– December, 2014
Page | 36
8.
XScope’s Examples
8.1
Resistor Voltage Divider
1)
Build the circuit shown on figure 59.
2)
Set the device to Meter mode
3)
You should see similar voltages as
shown on figure 60.
Theory of operation: The circuit is a voltage divider, where Vin is 5V, and Vout is the voltage at CH2:
𝑽𝒐𝒖𝒕 =
𝑽𝒊𝒏∗𝑹𝟏
𝑹𝟏+𝑹𝟐
8.2
Measurement of an RC time constant
1)
Build the circuit shown on figure 62.
2)
Set the time base to 500µs/div.
3)
Set the AWG to Square wave, 500Hz, 4V.
4)
Set the gain on both channels to 2.56V/div.
5)
The display should look similar to figure 61.
6)
Now set the time base to 16µs/div.
7)
Turn off CH1, set the CH2 gain to 1.28V/div.
8)
Adjust the horizontal and CH2 positions so that
the rising wave takes most of the screen.
9)
Turn on the vertical and CH2 horizontal cursors.
10)
Enable the cursors TRACK option.
11)
Set the first vertical cursor at the corner of the wave, and the second cursor where the voltage equals 0V.
12)
The display should look like figure 64. The measured time
𝑇
1/2
= 69𝜇𝑠
, is the “half-life” time, so
𝑅𝐶 = 99.95𝜇𝑠
Theory of operation: Circuit theory shows that if the RC circuit is fed with a step input, the output will approach a DC value
exponentially; figure 63 shows the equation from which we can obtain RC when the half-life value is known.
8.3
Half Wave Rectifier with Smoothing Capacitor
1)
Build the circuit shown on figure 66.
2)
Set the time base to 2mS/div.
3)
Set the AWG to Sine wave, 125Hz, 4V.
4)
Set the gain on both channels to 1.28V/div.
5)
The display should look like figure 65.
6)
If the capacitor is removed, the display should
look like figure 67.
Theory of operation: The diode will allow current to flow only during the positive half of the sine wave. The output voltage
is a little bit lower because of the voltage drop of the diode. When the AWG voltage is negative, the diode acts like an
open circuit and the capacitor discharges thru the resistor at an exponential rate.
Figure 59: Resistor divider
Figure 60: Meter mode
Figure 66: Half wave rectifier circuit
Figure 65: Half wave rectifier
Figure 67: Removing the capacitor
Figure 62: RC Circuit
Figure 61: RC Measurements
Figure 64: Half-life measurement
𝑽
𝒄
= 𝑽
𝟎
(𝟏 − 𝒆
−
𝒕
𝑹𝑪
)
𝑹𝑪 =
𝑻
𝟏/𝟐
𝐥𝐧(𝟐)
Figure 63: RC Equations