ankur_gajjar

Hello,

I want to implement PID temperature control using FB58 and for that, I've read SIMATIC PID temperature control manual. Now, my question is that what is cyclic interrupt and how does it work? What is cycle time and how it should be decided? If I want to use OB35 with OB1, how should I configure the cycle time for them? Besides, what's the difference between TCONT_CP and TCONT_S?

Regards,

Ankur

Hello ankur_gajjar;

The heater type you are looking for is a SCR (or Thyristor) heater/controller.

Search for "SCR heater controls" (for example) on the web and you will find many manufacturers and their operation manuals that explain the theory behind their operation.

You have to know that a SCR is a power transistor that can control the flow of power by changing the phase angle that it fires (allows power to pass) at. That is what your PLC controller will do, either with an analog signal or a digital pulse train (FB58 TCONT_CP) or withstep controls (FB59 TCONT_S), depending on the type of SCR controller you will purchase.

You will need to purchase the resistive heater circuit and the SCR controller from your nearest provider, decide what type of control you can use with it, and connect either an analog/pulse trainoutput (FB58) or a digital output (FB59) signal to the SCR controller.

This webpage for example shows how the change in firing angle of a SCR changes the power output to the heating elements, therefore controlling the heater output.

http://www.avatarinstruments.com/scr/scr.asp

We had great success with pulsed-type (on-off) controls of this type of controllers, using FB58 and these modules (but there are many other manufacturers you can work with):

http://www.kele.com/Catalog/22%20Thermostats_Controllers/PDFs/R820%20Technical%20Documentation.pdf

Hope this helps,

Daniel Chartier

ankur_gajjar

Dear Daniel,
Thanks for your reply and valuable input. The only thing I want to ask is that: whether I can do the same thing using Solid State Relay (SSR) or Optocoupler Relay? The only reason is why I am asking is that I having both of them at my disposal in fair amount. Besides, I have heard that SSR is great for this kind of application.

Regards,
Ankur Gajjar

What "same thing" are you asking about? Controlling a heating element in your process?

I think at this point you need to describe in detail what your application does, and how you wish to proceed. We are missing too many details to provide adequate answers, it seems.

Hope this helps,

Daniel Chartier

Hello ankur;

I have never devised such a system, basically because SCRs are power elements, and they are better suited in my understandingto control power in industrial applications.

However, it seems others have done PID control of resistive heating elements with SSRs (using high current SSRs) and have displayed their results on the web.

Do a seach on the terms "heating element controlled by ssr" (I used Google) and you can examione the proposed solutions.

Hope this helps,

Daniel Chartier