FB41CONT_C function and parameter setting of Siemens S7-300PID - Database & Sql Blog Articles

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Now use Siemens S7-300 (CPU315) to do the PID control of the rectification system, specifically input the 4-20MA signal by the AI ​​module (both A cabinet / B cabinet saturated reactor control current signal feedback and unit A cabinet / B cabinet DC current Signal feedback), through the CPU call PID function block, realize automatic closed-loop control, and finally the AO module outputs a 4-20MA signal to the steady current system (both A cabinet / B cabinet current given feedback).

problem found:

1. Which function blocks in the PID of S7 should be called specifically. Call FB41 directly in OB1, I don't know if it can.

2. How to set the input and output parameters of PID standard block FB41, what is the difference between PV_PER, SP_INT and PV_IN.

3. How to set GAIN, TI and TD.

4. How to use MAN_ON and PVPER_ON, is it written directly at the input of FB41?

In principle, the adjustment rhythm of the PID should be consistent with its sampling period, which is the requirement that the mathematical model should be consistent with the physical process. This is why FB41 should be called periodically in OB35 and the period of OB35 should be consistent with the sampling period of FB41.

Of course, it is also possible to call FB41 in OB1 or other FC and FB. In this case, it is better to use the scan period in the OB1 parameter area as the sampling period of FB41.

In the PID process control of constant current and constant pressure of pipeline, I also called FB41 continuously in FC unconditionally, and the PID effect is also satisfactory. I personally think that in applications with low precision requirements, simple calls are also possible.

The setting of FB41 parameters is very flexible and can be selected according to your own habits or application convenience. Here is a way.

MAN_ON: Activate the PID to manually adjust the enable bit of the set value MAN, which can be triggered by the PID hand automatic conversion bit.

PVPER_ON : is the enable bit of the PID input and output parameter "PERIPHERAL", that is, the parameter is regarded as an integer between 0 and 27648. To put it another way, the feedback value of the PID is taken directly from the corresponding AIW channel, and the PID output is directly given to the AQW channel. Parameter tuning is done by FB41. The start position of the adjustment device can be used to trigger the home position.

MAN : PID manually adjusts the set value and is valid when “MAN_ON=1”.

CYCLE : Sampling period. According to the change of physical quantity, the general requirement is consistent with the cycle of FB41 execution.

SP_INT: The set value of the PID. Note that the set value is consistent with the unit of the feedback value. In order to avoid errors, it is recommended to convert SP_INT to a dimensionless percentage between -100.0 and 100.0%. When inputting to FB41, be careful to take only the number before the percent sign.

PV_PER: The feedback value of the PID process is directly taken from the A/D code of the AIW channel of the feedback amount. Only valid when "PVPER_ON =1".

GAIN: The scale factor.

TI: Integration time.

TD: Differential time.

LMN_PER: The adjusted output of the PID directly corresponds to the adjusted output AQW channel.

With the above parameters set, the basic PID adjustment can be achieved. Complete other parameter settings as needed, such as dead zone settings.

Using the PID assignment tool in STEP7, the parameter settings can be completed graphically and quickly. The result is directly stored in the corresponding instance data block. FB41 does not need to be assigned when calling.