>> Could someone tell me how to regulate the temperature of a room
>> with a two-state heater (on/off), using the pid vi's.
In <7Ip2IV1cfjB@hhullen.btx.dtag.de> HHullen_BS@BTX.dtag.de (Helmut Hullen) writes:
>You don't need the PID. A simple 2-state control does the work.
^^^^^^ ^^^^^^^ ^^^^^^^
Frankly, I tend to agree. However, if you _need_ PID control and _if_
your two-state heater is solid-state switched, there are other
options. For example, commerical PID temperature controllers with
zero-voltage switching (ZVS) operate by generating a slow enabling
pulse, then achieving proportional control by varying the duty cycle of
this enabling pulse. For instanance, if your enabling pulse is running
at 10-Hz, with 50% duty cycle,
then your heating element will be on for
50% of the time every 0.1 second.
You can use a programmable timer (National includes two on their MIO
cards) to program the 5 or 10 Hz output and its duty cycle. You might
have LabView execute the PID subVI once every two or three seconds to
adjust the duty cycle on the programmable timer so as to minimize the
feedback error=(tempSetPoint-currentTemp).
Why are you wanting to use LabView for PID temperature control in the
first place? There are some very good PID temperature controllers
(programmable through a serial port) with built-in solid-state ZVSs
and readouts for $900 that you can buy. They'll fit right into
a control panel, display and all. Sure beats messing with a
programmable timer card and its outputs, plus you get a digital panel
readout to boot.
--
/\ Mark M Mehl, alias Superticker (Supertickler to some)
<><> Internet: mehl@IAstate.edu
\/ Preferred UUCP: uunet!iastate.edu!mehl
Disclaimer: You got to be kidding; who would w
ant to claim anything I said?
