Siemens S7-200 PID Control.

Hi all.

I have a S7-222 CPU with a 4 AI 1 AQ module attached to it. I have an oxygen sensor that is attached to AIW0 and a C02 sensor connected to AIW2.

The system also has three valves conected to the digital outputs.

The three valves control three gasses. Nitrogen, C02 and compressed air. The system is being used for a chamber where an exact level of O2 and C02 are needed.

I have two setpoints. Oxygen is VD100 and C02 is VD104.

I need PID control for the two gasses.

The system works as follows.

System is started and waits for 30s for the CO2 card to start. Oxygen sensor should be reading 20.9% in normal air. AIW scale is 0-50mV
There is a diagphram pump which circulates the Air from the chamber through a plenghium and also through the CO2 sensor and back into the chamber.

CO2 will be reading around 0.04%

Setpoints will be around 5% for both gasses. Nitrogen valve will open to flush out the Oxygen until it is 10% outside the setpoint. At this point the CO2 valve needs to be opened to flush out the nitrogen gas and also increase the CO2. When the CO2 reaches about 2.5% the O2 will be around 5% so air valve now needs to be opened to allow the oxygen to go back to 7.5% so that the extra 2.5% CO2 will lower the O2 to 5%.

The setpoint are not going to be changed often as these chambers are used for IVF and Stem Cell Research.

I have never worked with PID loops before so if anyone is able to help with this I am gratefull.

...circulates the Air from the chamber through a plenghium...

Click to expand...

through a what?!? That is an excellent word. The English language has long needed such a word. All we need now is a meaning for it. I've no idea what it is but it sounds as though it should be something good! Best new Word Of The Month by far, and a strong contender for Word Of The Year. (should be plenum?)

Oh, the PID? Sorry, not a clue.

regards

Ken

strong contender for Word Of The Year. (should be plenum?)

Click to expand...

That looks better for the spelling of the word. I didnt think that it looked correct when i typed it.

The S7-200 Series with MicroWin has a PID Wizard



Use this to set up your PID Loops

Then use the PID Tuner to tune your loops



See the Help files for explanations of all of these

Go to

MicroWin4 > Help > Contents and Index

Type in PID in Find, then scroll down in box 3 to see the various PID Helps Topics