On Fri, 6 Mar 1998 14:23:05 -0600 Calvin writes: >Comment: > >PID controls are inherently analog. This does not mean they cannot be >implemented digitally, but it is generally a lot easier to do it with >one or >two op-amps. It depends on what the process is of course. For simple fast processes I'd agree that analog can work well and digital offers no advantage (I won't go as far as to say that PID is "inherently analog" though). For example, I have a Magnavox CD player (ca. 1984) that uses op-amps throughout the servo loops that keep the laser beam on track on the disk. I suspect newer players still do this process mostly analog, it's just buried in the big chips. Analog has the neat feature that you can just wire in some potentiometers and unpluggable capacitors and play with it until the control is "optimized." This can be hard to explain to the boss though. On the other hand, if the process is slow enough that the time constants in the integrator and differentiator run to seconds or minutes, analog components to do that can get unwieldy. Or if you want or need to add various nonlinear special cases ("fuzzy PID" ???) it may be best to go digital. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]