Block diagrams and block diagram algebra have been discussed
in tutorial #3 [and the quiz review notes].
Block diagrams can be useful tools for:
Visualizing how a system works
Simplifying a set of system equations
and
Obtaining system transfer functions
That said, they are also potentially hazardous, since errors
in your block diagram formulation will propogate into later
system analyses!
Your first step in analyzing a system should be:
Itemize all Constituitive Equations
(which describe the system).
You can then represent individual equations as blocks, relating
some input to some desired output, and then these blocks link
end-to-end with one another.
OR, you can simply manipulate your equations to derive a
relationship between the desired input and output.
When creating a block diagram, there are really only two,
basic actions relating variables:
MULTIPLICATION (and/or division)
is accomplished by passing some input through a block.
(The input to the block is multiplied by the contents of the block to produce the
output from the block.)
ADDITION (and/or subtraction)
is accomplished at a summation junction.
(Two or more inputs to the summation junction are added or
subtracted, as indicated, to yield the output from the junction.)
To create accurate individual blocks, you may wish to put your equations in the form:
output = input * [some polynomial in 's', or a constant]
e.g.:
y = x * [a]
The output from one block then becomes the input to
the next (sequential) block.
Just recall that each block contains some
TRANSFER FUNCTION which always represents the
relationship: 'block_output(s)' / 'block_input(s)'.