Control Strategy

Does the instruction manual mention other strategies than just "fixed setpoint"? If so, even in the absence of "...feedforward...", there may be an intermediate scheme that would work.

heres for the DR20:

1. fixed set point controller

2. fixed sp controller w/ disturbance var feedforward at input

3. fixed sp controller w/ disturbance var feedforward at ouput and many more;

for the DR21:

1. fixed value/three-component controller/controller w 2 internal setpoints

2. slave controller

3. ration controller

4. control unit/process display

5. fixed value controller w 1 set point for control system coupling (as of software version-A7

6. slave controller w/ internal/external switching for control system coupling.

these are all the control strat of the DR21.

thanks 'tor

Hmm, that's quite a change between DR20 and DR21. What does DR21 mean be "ration controller"?

Just a simple typo. That function should read as, ratio controller.

From the description you supplied of the DR21, it doesn't appear that the manufacturer intended this to be a replacement for the DR20. I suggest that you talk with Siemens field service rep, since feedforward is a critical component for Boiler Control.

Take note that the DR24 specifically lists Boiler Control as one of its functions. The controller may be a bit of an overkill for you in terms of capabilities that it can provide and what you'll use it for, in addition to the cost. But it's hard to say what Siemens was thinking when they decided to no longer manufacturer the DR20. Again, you'll do very well to talk directly to the field service rep.

i have talked with siemens rep in the philippines about this concern and they seemed not to provide solutions. in fact they have seen the set-up of our boiler (DR21) and they seemed resigned in providing other solutions in using DR21 in our application.

thank you all for the immediate reply and very much appreciated. i hope there colud be someone who have had this problem before that can contribute solutions and recommendation. thank you guys