How Will We Measure 3 Voltages at Once
- To check that the CRO has been connected to the
circuit correctly is quite simple.
- We will use Coaxial
Cable to connect the CRO to the
circuit so that we need only worry about the connecions
made at the circuit.
Checking the Connections at the
- Below we see the diagram of the circuit with the
nodes labelled. The important nodes are Node2,
Node3 and Node4
since it is the GROUND node of the circuit.
- We will require the use of Both Channel A and
Channel B. Both
Channels will have their Negative Terminals connected to Node
- The positive terminal of Channel A will be
connected to Node 2
while the positive terminal of Channel B will be
connected to Node 3.
Why Connect In This Manner:
- The CRO is connected to the circuit in the manner
mentioned above so that all 3 voltages can be measured
without disturbing the circuit. This can be explained by
considering the following:
- The Voltage at Node 2
is the signal being applied to Channel A.
- This voltage is the voltage drop across
R2 and Also the voltage drop across the combined
resistance of R3 and R4.
- The Voltage at Node 3
is the signal being applied to Channel B which is
equal to the voltage drop across R4.
- So to find the Voltage drop across R2
we simply move the Mode
Selector to the CH A selection. And
then to find the voltage drop across R4
we move the Mode
Selector to the Channel B position.
- Now it is obvious that the Voltage drop across R3
is simply the voltage at Node2
minus the voltage at Node 3.
- This voltage can be calculated or simply read
from the display
by moving the Mode
Selector to ADD and inverting
Channel B by "pulling out" the Vertical Position
Control of the trace.
- If the above requirements have been satisfied it
is time to make the measurement of the D.C. voltage.
to CRO Menu
Page maintained by EIE WebMistress
Revised: 15 September 2004