Connecting the CRO to a Circuit
- The CRO like any other measuring device, is
useless if there is no method available to transfer the
signal we wish to measure to the CRO itself.
- As far as the CRO is concerned there are three
types of cable that can be used to connect the CRO to the
circuit of which we wish to take readings. These are:
- Coaxial cable is the most convienient connection
device for taking readings.
- As the diagram below shows, one end of the cable
has a BNC connector which fits directly onto the input of
- While the other end splits into both a Red
Positive and Black Negative cable.
- The above cable due to it's thickness contains a
great deal of Stray Capacitance, this in turn causes the
distortion of extremely small signals.
|Things to Remember About Coaxial Cable
- Always connect
the Negative cable (Black) to the GROUND point of
- This type of cable is not useful for very
small signals (around 1mV).
- The most convienient of the above types
of cable as we only require one cable for each
input channel of the CRO.
2. 3mm Cable:
- This type of cable differs from both the Coaxial
and the X10 probe in two ways:
- We require two 3mm
cables for each CRO input (one positive and one
- The 3mm
cables cannot be connected directly to the CRO,
this means that we require the use of a BNC
to 3mm adaptor. This adaptor
is shown below on the right of the 3mm
- When we look at the diagram above we see that the
adaptor has two terminals. The terminal marked as (-) in
BLACK is the Negative Terminal and should always be
connected to the GROUND node of the circuit we are taking
- Now the other terminal marked as (+) in RED is
the Positive Terminal and should be connected to the node
at which we wish to find the voltage.
- Finally the BNC connector needs to be connected
to the CRO input itself.
3. X10 Probe:
- Here we have the most sophisticated of the
connection devices, it is really only used when we
require very accurate measurements.
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Revised: 15 September 2004