While preparing the graphic diagrams trend display, 3 types
of trends are prepared by Yokogawa system vender. These are
for process variable, manipulated variable & set point
Why these 3 trends are required? Explain the purpose of
these 3 trends.
Answer / dev
This is process control related que.
First, process variable is what we need to measure for
specified process. Suppose, water tank in which exit temp.
is to be measure then temp. is our process variable for what
we are doing the process.
Second one, manipulated variable is what we use its value to
control the process variable. Taking the above ex. of exit
temp. water tank process then manipulated variable is the
most effective parameter which affects the exit temp.
sensitively say water flow in the tank, then the water flow
is the manipulated variable for temp. control..
And the third and last is, the set point, which is our motto
for the process. i.e. in above ex. exit temp. should not go
beyond the set point. We have to maintain the set point to
restrain the damage.... practically process variable always
fluctuates or may get set point but remember that it won't
This all variables are considered mostly when we use
cascade control in the single process...
Hope it will explain why all the variables are imp. for
process.. if not yet then u can mail me
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