Variable limit for analog output

Dear all

I am trying to achive the following:

When digital signal is low/off (in this case same as Q2) an ananlog output AQ1 have a range of min 200 and max 1000.

When same signal is high the analog output AQ1 is now limited to min 200 max 750.

I have somewhat achived it in attached logic, however, as I have used a simple mathematical instruction my min. setting of 200 is not working (when the B018 is high). When B018 is low the min/max of 200 and 1000 is working.

Any ideas?

This works perfect.

As a backgorund for the problem I found out that when running my wood pellet burner in series with my temperature shunt I would get a very big overshot on the regulation if I did not limit the output, meaning the wood pellet burner would shut down and start again very shortly after. When I run my normal wood burner I still need the shunt to be able to open fully (1000).

I am using this simple program to test these functions and incorporates them as I go along in the T1/T2 reverse function.

Thanks for you help!

Hi ixo

I've been playing around and have found (in my opinion) a better solution by using a 2 amplifyers and 1 MUX. This setup ensure that the PI regulator uses it's entire band - e.g. in your solution the PI controller would still ramp down to 0 even though the AQ was limited to 200 (and vise verse to 1000) By using the two amplifyers the PI uses the entire band. See attached and let me know what you think :)