How to use the pressure transmitter of feedback to control the system pressure constant pressure? - - - - - -

is already the very mature and widely used PID control technology, in terms of pressure closed loop control system, implementation of the method also has a lot of, such as the use of frequency converter internal PID control function, PLC controller, the features of the PID and the PID controller, and so on. This paper tells S7 - 200 SMART PLC controlled by PID self-tuning function ACS550 inverter drive screw pump, the pressure transmitter of feedback to control the system pressure constant.

S7 - 200 CPU provides eight loop PID function, to need according to the automatic adjustment of PID control rule control tasks, such as temperature, pressure and flow control, etc. PID function need analog input, to reflect the actual numerical controlled quantities, known as the feedback; Of adjustment target, set by the user and is given. Task of PID arithmetic is given according to the feedback of relative difference, according to the law of PID arithmetic to calculate the result, the output to the frequency converter ( Drive pump) Adjusted by the enforcement agencies such as to achieve automatic maintain controlled with a given amount of change.

let's look at the principle of PID self-tuning and conditions:

programming is very convenient, simply execute PID guide step by step operation.

click tools - — PID can begin PID guide configuration, configuration here two sets of PID LOOP, LOOP and LOOP 1 0

preliminary PID parameter configuration, here to default, because behind have a PID control panel can be adjusted.

step by step is completed, will be automatically generated the PID subroutine, PID0_CTRL and PID_EXE interrupt procedures, the former need to use SM0 in the program. 0, which the system automatically calls, use timer interrupt to achieve PID algorithm is completed on time.

in the program invocation:

simple introduce: PV_I as the measured value, if the measured pressure is the pressure transmitter feedback analog channel.

Stepoin: value variable addresses, enter 0 The value of 1, 0 - for the full scale 100%, such as the range of 1. 6 mpa, need the whole set to 0. 8 mpa, then here to enter 0. 5

AUTO ~ : the use of PID in PID guide manual function, there is this option, conditions on, is the PID output manually.

Manual ~ : Manual output value, enter 0 1, corresponding to 0

100% Output: the Output analog, namely control the frequency of the inverter.

above is complete, enter the PID debugging stage, S7 - 200 SMART configuration PID control panel, make the PID adjustment appears more intuitive.

general use can adjust the PID self-tuning, the panel feedback PID trend diagram, of course, also can be used to manually adjust the function of PID. PID control is not the so-called experience value, you can refer to the following have some flaws.

may be someone will notice, S7 - 200 SMART PID adjustment need to open the computer and application, connect the configuration, and even if it is manual adjustment. So how to through the HMI ( Touch screen) To set the PID parameters? To this end, the author specifically to find adjusting entry for your reference: actually generate subroutines in by PID guide at the same time, also has created the PID parameter variables.

as shown in figure, VD312 is p ( Gain) VD320 for I ( Integration time) VD324 for D ( Differential)

then placed on the HMI these addresses, can be directly into the PID parameter values, of course, to display the trend diagram, can be configured on the HMI a trend chart, analog feedback effects like online connection PLC panel Settings. ACS550 accept the current signal of PLC analog output channels, to drive the motor, reached the requirements of control, for the inverter, the control system, turns to be a performer.

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