helpme@ram

Dear Experts,

I need to know how to use FB 58 for cooling process. ?My application is simple, i need t0 control temperature for DRI material, DRI material temperature should always be around 30 degrees. and if temeprature exceeds i need to control a nitrogen valve, so that it increases more flow rate of nitrogen and cools the material..

I used Siemens Block FB 58 and for simulation purpose i used FB 102 block( HEat simualtion Block) and i was successful in simulating it,. Now i need to use the block FB58 for cooling purpose with the Simulation block (FB102) for testing purpose, i know in real time i will be eliminating FB 102 block, but as of now i need to simulate and test, so am using it..

Please tell me how to use FB 58 for Cooling.. If i need to give gain as negative, please let me know the steps to do it. Sorry if am asking stupid question.. This is my first project with PID, i am just a beginner..

helpme@ram

Hello Hdhosseini,

Actually i used a negative Gain.. and the resultatnt output was as follows..

i) When i keep set point to 20 Degrees , it decreased the PV the from high level to the specified set point, but the Corresponding LMN_PER output variable also decreases .
ii)As i said my appliation is to control temperature, i give temp as PV_IN and control the nitrogen flow valve , if temperature needs to get decreased there should be more nitrogen available

iii) but when i use negative gain, it doent help me, the PV output comes to set point, along with it LMN_PER output also decreases , but i need LMN_PEr output to increase so that to cool the temperature i will increase the flow rate of nitrogen, which is possible if i give more current to Analog card( for ur info my range is 4-20mA).

may be am doing it wrong, please correct me if am wrong..

helpme@ram

Hello hdhosseni,

As you said, i checked my Error, its in negative(for both positive gain and negative gain), but when i use negative gain, and give set point of 50, the PV out goes to maximum valuve 100 and stops and LMN is 27648.. Strange behavious

Am i doing it wrong?? can u pls explain a little bit more.. with positve gain it works fine for heating. No problem...

helpme@ram

Hello hdhosseini,

i) I change the set point through VAT table.. And intially i do Auto Tuning Once i start the program at starting day, i do these Auto Tuning by opening the DB 58 ( And in my case its DB1, and here on i will be refering DB1) and select options Cotroller tuning , so once its finished i neither change my gain again, after that i will change just the set point ..

ii) I do not run manually, i just set it to AUTo and run the controller..

iii) Yes PV is greater in set value, i am doing simulation, and i always take care that Process Value is greater than Set Point, and my error is negative..
the addresses are as follows

Set_point =DB1.DBD 34

Gain =DB1.DBD 166

error=DB1.DBD 92

Please find the attached project, i have created Db1 which is instance of FB58.