How to implement PID in s7 300 PLC?

amruthkiran

Member
Join Date
Jul 2009
Location
India
Posts
6
e have a TMT system for our steel plant.
TMT stands for thermomechanical treatment system. It is a water cooling system for cooling the steel rods. The steel rods will pass through the TMT in milliseconds. I have to control the outlet temperature of steel rods coming out of TMT using water cooling.
Inputs available:
1. Input temperature(4-20mA) of steel rod before TMT (Pyromter input)
2. outlet temperature(4-20mA) of steel rod before TMT (pyrometer input)
3. Flow rate (4-20mA) from magnetic flowmeter
4. Pressure sensor input
Analog Output
1. Flow rate control using 4-20mA input to flow meter

I have to program TMT in such way that outlet of TMT should be maintanied at 250 degree C by controlling the flow.
Please provide some tips to program the TMT.
Can I use PID control for this purpose?
How can i implement PID control in s7 300?
I have no hardware PID controller. I have to create a software PID controller.
Please provide some tips to program the PLC
 
If you're talking about rolling mills, a normal PLC is not fast enough for this job (although under the right circumstances a VIPA or Siemens 319 might just manage it if lightly loaded).

There is at least one caompany who make specialised controlers for this purpose - unfortunately, I can't remember their name at present. :( If you browse the net long enough you should be able to find some references.
 
Hi there
How much time in milliseconds??
Whats the current scan time of the PLC??

To get you started you can search over here using the key words like "FB41", you will be overwhelmed with number of hits !!
 
You will need to use feed forwards. This should get you close but you need to know the temperature of the coolant water too. It takes time ( many milliseconds ) for the water spray to hit the steel. This will show up as a dead time. However, you can use the data from the rod before to make adjustments for the next rod.
 

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