Devices Used to Connect Circuits

In the laboratory we define Connection Devices as the wires used to connect circuit elements such as resistors, sources and measuring devices together.

Now there are three basic types of connection devices in use within the First Year Laboratory, these are listed below:

This type of cable derives it's name from the size of the plug it has at each end.

When 3mm cable is used we have the following constraints:

We require two 3mm cables to connect sources and measuringdevices to the circuit (one positive and one negative).
The 3mm cables can be connected directly to the DMM and D.C. Power Supply as both of these devices hav 3mm plug inputs and outputs respectively.
The 3mm cables cannot be connected directly to the CRO Input or Function Generator Output because the inputs of these devices use of a BNC connection. For this reason we need a 3mm to BNC adaptor. This adaptor is shown below on the right of the 3mm cables.

When we look at the diagram above we see that the adaptor has two terminals. The terminal marked with the (-) is the Negative Terminal an should always be connected to the GROUND node of the circuit we are taking readings from.

Now the other terminal marked with (+) is the Positive Terminal and should be connected to the node at which we wish to find the voltage.

Finally the BNC connector at the bottom of the adaptor needs to be connected to the CRO input itself.

Coaxial cable is the most convenient connection device for taking readings using a CRO and providing an A.C. source using the Function Generator.

As the diagram below shows, one end of the cable has a BNC connector which fits directly onto the input of the CRO or Function Generator .

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 the circuit. This type of cable is not useful for very small signals (around 1mV). The most convenient of the above types of cable as we only require one cable per BNC connection rather than the two required by the 3mm cables. Coaxial Cable cannot be used with D.C Power Sources or the DMM.

Here we have the most sophisticated of the connection devices, it is really only used when we require very accurate measurements in Digital Systems or Small Signal Electronics.

It is only used to make measurements in conjunction with a CRO.

In the diagram below we see that the CLIP on the side of the Probe must be connected to the GROUND Node of the Circuit.

The TIP of the Probe should be attached to the part of the circuit at which we wish to make a measurement.

Finally the Probe can be used to amplify the signal it is being used to measure by a factor of ten. This is done using the switch on the side of the Probe.

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Revised: Friday, 17 July 1998