Maximum number of ET200's and PID blocks?

I'm writing my final exams paper and is making my program on a Siemens S7-1200 PLC. My program is for Greenhouse's and is built so it is possible to quickly configure many Greenhouse's. I'm using a 1214 PLC and 3 ET200S. My question is: How many ET200's is it possible to control? Is there any limit? I also would like to know how many PID block the PLC can handle? I have looked on the forum and read a guy saying it can handle 16 PID block, but then I found another post from a guy how had tested it and got up to 41 PID blocks. So what is the right answer?

Hope someone can help me.

Regards

Hello Mads;

These are 2 separate and distinct questions.

You can have up to 125 remote IO ET 200 stations if they use Profibus-DP as a network; if you choose Profinet, it will depend on your configuration (ring topology, Shared Devices, I-Devices...), but you can count on many nodes.

PID in the S7 controllers are instruction-based, so the maximum number of PID blocks depends on the size of your CPU work memory (calculating the size of the PID block and the associated instance DBs).. So I am not very surprised that someone will claim up to 41 PID blocks, although it would require some attention to cycle durations to make sure you do not cause a watchdog fault.

Here is what the S7-1200 system manual has to say as an introduction to PID instructions;

9.2.1 Inserting the PID instruction and technology object

STEP 7 provides two instructions for PID control:

● The PID_Compact instruction and its associated technology object provide a universal PID controller with tuning. The technology object contains all of the settings for the control loop.

● The PID_3Step instruction and its associated technology object provide a PID controller with specific settings for motor-activated valves. The technology object contains all of the settings for the control loop. The PID_3Step controller provides two additional Boolean outputs.

SIMATIC S7 S7-1200 Programmable controller

Hope this helps,

Daniel Chartier

Thank you very much for your answer. It was very helpful.