Time dependent temperature control

Hi guys.There is a batch reactor .Reactor is charged via two holes in the top of the tank; while reaction is carried out, nothing else is put in or taken out until the reaction is done; tank easily heated or cooled by jacket.I want to control this system via S7-1200 plc.Time-dependent heating or cooling will be performed according to the values entered on the screen.Is it possible this type plc ?,if answer is yes,are there any relevant blocks in the library?Thanks in advance..

tulip said:

Time-dependent heating or cooling will be performed according to the values entered on the screen.

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That's a loaded question. Many batches need to heat up or cool down at specific rate, and many times there might be periods where a steady temperature is maintained before advancing to another heat or cool action.

Doing so requires an automated change of the temperature setpoint for the duration of the ramp up or ramp down. The feature is called something like "setpoint programming".
The ramp-up, hold, ramp, hold ramp sequence is commonly called a setpoint profile or a setpoint program.

A control scheme can include features like 'hot start' where the ramp-up starts at the current process temperature value, instead of starting at whatever the ramp value is (saves batch time).



There's a short blog on it here:
http://blog.west-cs.com/blog/understanding-setpoint-ramping-and-ramp/soak-temperature-control

These types of operations have been worked out for stand-alone Setpoint programmer controllers which are now mature products. It might be worth reading the manual of one to see what is offered so that you can determine what your application needs to implement before you finish the project and have the user say, "but we really need to do . . . "

Here's a typical 1/4 DIN Heat/Cool setpoint programmer:
http://www.west-cs.com/products-uk/models-uk/pro-ec44-single-and-dual-loop-temperature-controller/



That particular unit can be dual loop control for cascade control, which is not an uncommon control algorithm on jacketed tanks.

The temperature control is typically done in the PLC (PID control, switching from heating to cooling valves) HMI, but the automated ramp-up/ramp down functions are accomplished either in the HMI or in more specialized PLC function blocks, like PACs have. I do not know whether that Siemens PLC has setpoint programming functionality or not. An HMI is needed to select which profile runs, and to implement halt, resume and abort functions.