martin griffith said:
I'm not that good at PIDs( ie useless), but one thing confused me, is
the input differential or single ended?
what was the original input circuit?
martin
The circuit should be taking a "command" voltage on one input, and an
"error" voltage on the other, and will generate a "control" voltage on the
output (with commerial PID controllers, these are usually 4-20ma or 0-10v
signals, center neutral)
I've done PID in software, so I know the theory, but have no idea how that
translates to op-amp hardware !!
you need to be looking for 3 things
the P term is multiplicitive so it will probably be represented by one of
the resistor/capacitor nets, same thing for the I term.. the D (which I know
as damping rather than differentiation) is usually subtractive and is
probably represented by the resistor divider that the top of the schematic.
This next part is referenced to servo motor motion control systems
so -- when the command and error voltages are not equal, this is going to
generate a command voltage that is used to activate a servo driver -- the
servo driver uses the absolute magnitude of the signal to set the PWM duty
cycle (for DC motor systems) or to set the AC frequency for AC servo
motors., and the polarity (around the center of the voltage/current range)
to determine direction
the P term causes acceleration, which, the longer the inputs are unequal,
the I term will magnify (it is multiplicitive and cumalative), attempting to
give a little more UHMPH to bring things back into sync, while the D term
takes over during deceleration (as the command and error voltages converge)
reducing the command output so that things coast smoothly to a stop.
Now for the fun part -- identifying which parts of that circuit handle each
part of the process -- and that I am absolutly unable to help you with at
all !!
I guess I can make a guess -- the network on the op-amp input might be the P
term.. the resistor net is the D term, and the res/cap net right below that
the I term......
alternativly -- P net on the input -- everything above the op-amp is the I
term (with protection for integrator runaway, a common problem when the I
factor is set too high), and the net on the output below the op-amp might be
the D term.
Good Luck !!