I have a 1500W 208V heater I want to control with a PID controller. I was wondering if there are linear drivers available for this. Is this a standard way to control heaters this size? I am looking for precision with good error rejection so I need some sort of PID.

 

Hi Doug;

There are cycle counting controllers and phase controllers that have a more or less linear transfer function. For efficiency's sake I doubt that there is an actual linear control that provide full cycle variable amplitude sine waves. This isn't a problem because thermal time constants are almost always much longer than the period of a 60Hz. line. Phase control is preferred for short time constants or loads that don't integrate well (low thermal mass). Burst (cycle counting) controllers depend on long time constants to integrate the bursts.

Hope this helps

Curt Wuollet

 

Usually, you would use a PID controller with a time proportional digital output to control the duty cycle of a solid state relay or SSR. An SSR
with a zero crossing circuit will have much lower electrical noise.

When you use a SSR, you can use a short time period for your heater on/off cycles. This will approximate a linear heater due to the long time
constants in most heating applications.

If you are trying to heat something with a very small mass, such as a heated wire, you may need to use a linear heater controller, commonly
known as a SCR controller. These control the phase angle of each AC cycle. These require a PID controller with an analog output.

Companies such as Eurotherm, Barber-Colman , and Watlow are the ones that I remember had these types of products.

Bill Sturm

 

Look at SCR's from Hoffman Controls in Carrollton TX
http://www.hoffmancontrols.com/

Not exactly linear, but pulse width modulated on about a 3 second time base with zero-cross switching for far greater efficiency. The
resultant control is pretty linear.

Bill Gausman
System One Control, St. Paul, MN USA

 

> Usually, you would use a PID controller with a time proportional digital output to control the duty cycle of a solid state relay or SSR. An SSR > with a zero crossing circuit will have much lower electrical noise. HOW MUCH ELECTRICAL NOISE CAN THE SSR INTRODUCE IN A TERMOCOUPLE WHICH IS EMBEDED INSIDE A CERAMIC HEATER? ENOUGH TO DISTURB A PPLC MODULE?