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

YSZK type pressure sensor consists of diffuse silicon press inductor and linearity/temperature equalize convert circuitry, its characteristics are high measuring precision、good stability、better dependability、long life etc. Its encapsulation is stainless steel crust, small cubage, installed conveniently. They can be used for measuring pressure of various of medium of liquids、gas in ship and other industrial equipment.Taizhou Jiabo Instrument Technology Co., Ltd. PID control is now a very mature and widely used technology. For the pressure closed-loop control system, there are many ways to implement it, such as using the PID control function inside the inverter, the PID function of the PLC, and the PID controller. In this paper, the S7-200 SMART PLC controls the ACS550 inverter to drive the screw pump through the PID self-tuning function, and the pressure of the Pressure Transmitter is used to control the constant pressure of the system.

The S7-200 CPU provides eight loop PID functions for control tasks that require automatic adjustment according to the PID control rules, such as temperature, pressure and flow control. The PID function requires an analog input to reflect the actual value of the controlled physical quantity, called feedback; and the user-set adjustment target value is given. The task of the PID operation is to calculate the result according to the PID calculation rule according to the relative difference between the feedback and the given, and output it to the actuator such as the inverter (drive pump) for adjustment to automatically maintain the controlled amount to follow the given change. purpose.

Let's take a look at the principles and conditions of PID self-tuning:

It's very convenient to write a program, just follow the PID wizard step by step.

Click on the tool - PID to start the PID wizard configuration, here are two sets of PID loops, LOOP 0 and LOOP 1

Configure the initial PID parameters, which can be left alone by default, because there is a PID adjustment panel that can be adjusted later.

Step by step, that is, the subroutine of PID is automatically generated, PID0_CTRL and PID_EXE interrupt the program. The former needs to use SM0.0 in the program, the latter system automatically calls, using the timed interrupt to achieve the PID algorithm completed in time.

Call in the program:

Briefly introduced: PV_I is the measured value, if the pressure is measured, it is the analog channel fed back by the pressure transmitter.

Stepoin: Set the value of the variable address, enter the value of 0-1, corresponding to 0-100% of the full scale, such as the range of 1.6MPA, if you need to set to 0.8MPA, then enter 0.5 here

AUTO~: If you use the PID manual function in the PID wizard, this option is available. If the condition is turned on, it is the manual output of the PID.

Manual~: Manual output value, input 0-1, corresponding to 0-100%

Output: Output analog quantity, which is the frequency of controlling the inverter.

All of the above are completed, and the PID debugging phase is entered. The S7-200 SMART is equipped with a PID adjustment panel, which makes the PID adjustment more intuitive.