Application of EC20 Series PLC in Aging Room Control System

I. Overview

This article introduces Emerson's EC20 PLC application in the aging room control system and focuses on the realization of the PID closed-loop function in the constant temperature control and the powerful network communication function to realize the EMERSON EV2000 inverter operation control. The aging room control system is an important equipment for product testing in home appliances, electronics, and computer industries, and is an important part of product quality inspection. The system uses EMERSON EC20 PLC and multiple EV2000 inverters to achieve centralized control of indoor temperature and inverter operation.

Second, aging room control system process requirements:

Aging room structure as shown in the figure:

Specific requirements are as follows:

1. The area of ​​the aging room controlled by this system is 16×30M, the required control range is 20-55°C, the control precision is ±5°C, and the temperature can be set/displayed/saved in the upper computer; (Humidification control is used separately Has nothing to do with PLC)

2, The system has 3 fans for inlet, return and exhaust; 4 wind gates: new air lock, return air lock, exhaust damper, fire damper; 2 dust filters; 6 fires Alarm point

Under normal conditions (temperature and humidity), close the intake valve and exhaust valve, stop the intake motor and exhaust motor, open the return valve and fire damper, and start the return fan to maintain the return air circulation in the aging room;

In the high temperature conditions, the exhaust valve and the intake valve are opened, the exhaust motor and the intake motor are started, and part of the air is drawn out;

In the case of a fire alarm, the fire damper is closed, the return air is prohibited from circulation, and all are drawn from the room; at the same time, the exhaust valve and the intake valve are opened, and the exhaust motor and the intake motor are started to draw out the indoor air;

3, other requirements are omitted;

Third, the working principle:

The PLC system structure is as follows:

EC20PLC equipment I / 0 wiring as shown:

working principle:

According to the technical requirements of the aging room, the control system is composed as shown in the figure above: The upper computer adopts Taiwan Advantech IPC (Industrial Computer); the monitoring screen adopts the KINGVIEW software from Asian Control. The software is simple in operation, with rich component images and stable performance; the core control part adopts EMERSON EC20. -2012BTA type PLC and 4 temperature acquisition modules (EC20-4TC, receive K type temperature signal); drive uses EMERSON EV2000 general-purpose inverter.

In terms of device connection, EC20 PLC fully embodies its own advantages, because EC20 PLC itself has 2 serial communication ports (1 RS232 port, integrated free protocol / programming protocol / MODBUS slave protocol, 1 RS232/485 port , integrated free protocol / MODBUS master / slave protocol), EC20 PLC uses COM0 port and IPC to communicate (EC20 PLC slave station, set up as a MODBUS slave protocol), using COM1 and multiple inverters to form a network for centralized control (COM20 PLC's COM1 is set to MODBUS master protocol).

IPC is the man-machine interface of the whole system. IPC reads the system running status collected by PLC, such as the running status of each fan, the temperature of each temperature measurement point, the alarm status and displays on the monitoring screen. IPC also transmits various operation commands to PLC. To control the operation of the system, such as temperature settings, PID parameter settings, the opening and closing of various valves, start and stop the inverter and other settings. And can be real-time monitoring of the entire system's working status, action process and fault alarm, etc. IPC can also save and print the collected data according to the settings.

In the system design, EC20 PLC is the core of the whole system and performs various system operations and calculations. EC20 PLC makes logic judgments according to process requirements and field conditions, opens and closes various valves and starts and stops each fan; meanwhile, it uses its own PID function. The temperature is controlled and the specific method is described later.

EV2000 series inverter has its own communication unit with RS485 interface, which conforms to RS485 communication standard and is used to realize the networking of PLC and multiple inverters. According to the MODBUS communication protocol, we can easily implement the operation control of the inverter through the RS485 network. Because the RS485 communication link has long transmission distance, simple wiring, strong anti-interference ability and high reliability, in the design, we have omitted the external start and stop control circuit of the inverter. All the control of the inverter is through the RS485 communication chain. The road was completed to achieve a cost-effective purpose.

Fourth, the monitoring screen

The entire system monitor screen is mainly divided into the main screen, real-time temperature monitoring, PID parameter settings, three parts (other parts omitted), as follows:

The main screen is as shown in the figure above, and it mainly completes the monitoring of the system status (such as the opening and closing status of various dampers, the operating status of the fan, and the alarm status), and statistics (such as the time the system is running, the number of times the system is started or stopped). Temperature setting/measurement and other functions.

Real-time temperature monitoring screen As shown above, this screen is mainly used for real-time monitoring of temperature, and depicts the trend of temperature curve, in order to judge whether the temperature control of the system is in a good state, and at the same time, it can achieve operations such as saving/printing temperature.

The PID parameter setting screen is mainly used for the proportional constant P, the integral constant I, and the differential constant D. At the same time, it is adjusted according to the status of the real-time temperature curve; at the same time, the output ratio of the PID control is displayed.

Fifth, the realization of temperature control

In order to facilitate the control of the temperature inside the aging room, while taking full advantage of the PID function of the EC20 PLC and the PWM pulse output (Y0, Y1), the indoor temperature zone is divided into two parts (8 temperature points in the upper and lower layers). Measure the temperature as the measured value of the temperature, and send the average value to the PID function block for calculation. At the same time, the heating actuator (refer to EC20 PLC I/O wiring diagram, solid state relays SSR1, SSR2, SSR3 control The power of the heat pipe is gradually increased. The group processing is also carried out: when the temperature deviation is small, PID operation is performed, Y0 output pulse is sent to SSR1, and SSR2, SSR3 (that is, Y1, Y2 stop output); if temperature If the deviation is large, Y1 and Y2 also participate in the output. The specific processing ideas are as follows:

Through this method, the temperature control accuracy can be kept within ±0.3 degrees, and both the rising temperature and the falling temperature are very fast. At the same time, the PID output is converted into the PWM duty cycle output, which greatly saves the PLC's resources. Y0, Y1 up to 100KHZ pulse output function).

EC20 PLC's programming software CONTROLSTAR is easy to operate, rich in instruction, and powerful. It is a very good all-Chinese editing tool.

The implementation steps are as follows: First, the PID parameters are set in the data block, where the focus is to set the P, I, D three parameters and the output range of the upper and lower limits, because the PID output directly combined with the PWM, so Pay special attention to the settings, in this example, according to the PWM cycle is 4 seconds (= 4000MS) calculations, the PID output upper and lower limits are set to 4000 and 0; In addition, according to reverse action (BIT0 = 1), the output limit (BIT5=1) Requirements Assignment to D7911 Bits;

D7910 500 // Sampling time S3 The sampling time (Ts) range is 1 to 32767 (ms), which cannot be performed for a time shorter than the operation cycle.

D7911 16#23 //action direction> reverse action, set output limit

......................................................../BIT0 0: Positive action 1: Reverse action;

......................................................../BIT1 0: The input change amount alarm is invalid 1: The input change amount alarm is valid;

......................................................../BIT2 0: The output change amount alarm is invalid 1: The output change amount alarm is valid;

......................................................../BIT3-4 Not used;

........................................//BIT5 0: Output value upper/lower limit setting invalid 1: Output value upper/lower limit setting is valid;

......................................................../BIT6~BIT15 Not used

D7912 70 //S3+2 input filter constant (α) range 0～99[%], when it is 0, there is no input filter;

D7913 100 //S3+3 Proportional gain (Kp) range 1 to 32767 [%];

D7914 25 //S3+4 Integration time (TI) range 0 to 32767 (×100ms), when 0 is used as ∞ processing (no integration);

D7915 0 //S3+5 Derivative gain (KD) range 0 ~ 100 [%], when it is 0, there is no differential gain;

D7916 63 //S3+6 Derivative time (TD) range 0 to 32767 (×10ms). When it is 0, there is no differential processing;

D7925 2000 //S3+15 input change (increase) alarm set value from 0 to 32767 (When BIT1 of S3+1=1);

D7926 0 //S3+16 Input change amount (minus side) alarm setting value 0 to 32767 (When BIT1 of S3+1=1);

D7927 4000 //S3+17 output change amount (increase) alarm setting value 0 to 32767 (when S3+1 BIT2=1 and BIT5=0); output upper limit set value -32768 to 32767 (S3+1 BIT2=0 and BIT5=1);

D7928 0 //S3+18 Output change amount (minus side) alarm setting value 0 to 32767 (when S3+1 BIT2=1 and BIT5=0); output lower limit set value -32768 to 32767 (S3+1 BIT2=0 and BIT5=1);

Secondly, the PID instruction and PWM instruction are called in the program to control the output of Y0 (the logic control output for the comparison of SV and PV is relatively simple, so it is omitted here).

Sixth, start and stop control of the inverter

Because EMESON EC20 PLC and EV2000 inverter (non-standard) are all integrated with MODBUS protocol, it is relatively simple to realize their communication. The entire network adopts RS485 communication mode.

1. Set the communication parameters of each device interface and set the following for the EC20 PLC:

2. EV2000 setting points: 1. Each communication parameter must be consistent with the EC20 PLC. 2. The address of each inverter must have its own unique slave address. 3. Note that the communication jumper switch CN14 of the inverter is set in the RS485 direction;

3. The connection between EC20PLC and frequency converter is as follows:

4. Communication between EC20 PLC and frequency converter adopts MODBUS RTU mode. Modbus adopts "Big Endian" encoding method, which first sends high byte and then low byte. The RTU format is as follows:

RTU mode: In RTU mode, the idle time between frames is the larger of the function code setting and Modbus internal convention value. The minimum inter-frame idle time agreed in Modbus is as follows: The frame header and frame end define the frame by the bus idle time not less than 3.5 bytes. The data check adopts CRC-16, the whole information participates in checking, and the high and low bytes of checksum need to be exchanged and sent. For specific CRC check, refer to the example behind the protocol. It is worth noting that the bus holding at least 3.5 characters between frames is free, and the bus idle between frames does not need to accumulate start and end idle.

The main function of Modbus is to read and write parameters. Different function codes determine different operation requests. The drive Modbus protocol supports the following function code operations:

function code

Function code meaning

0x03

Read the function code parameter and running status parameter of the inverter

0x06

Rewrite single inverter function code or control parameter, do not save after power off

0x08

Line diagnosis

0x10

Rewrite multiple inverter function codes or control parameters, do not save after power off

0x41

Rewrite single inverter function codes or control parameters, save after power off

0x42

Functional code management

Different function codes of the Modbus protocol have different data formats and meanings. They are briefly described as follows:

Rewrite format protocol of multiple inverter function codes and status parameters: The request format is as follows:

Application layer protocol

Data unit

Data length

(bytes)

Value or range

function code

1

0x10

Start register address

2

0x0000~0xFFFF

Number of operating registers

2

0x0001~0x0004

Register contents bytes

1

2* operating register number

Register contents

2* operating register number

The response format is as follows:

Application layer protocol

Data unit

Data length (bytes)

Value or range

function code

1

0x10

Start register address

2

0x0000~0xFFFF

Number of operating registers

2

0x0001~0x0004

Read the protocol format of the inverter parameters: The request format is as follows:

Application layer protocol

Data unit

Data length

(bytes)

Value or range

function code

1

0x03

Start register address

2

0x0000~0xFFFF

Number of registers

2

0x0001~0x0004

The response format is as follows:

Application layer protocol

Data unit

Data length

(bytes)

Value or range

function code

1

0x03

Read bytes

1

2* register number

Read content

2* register number

The function code parameters, control parameters, and status parameters of the drive are mapped to Modbus read and write registers. The reading and writing characteristics and range of the function code parameters follow the instructions of the inverter user manual. The group number of the inverter function code is mapped to the high byte of the register address, and the group index is mapped to the low byte of the register address. The inverter's control parameters and status parameters are virtual inverter function code groups. The correspondence between the function code group number and the high byte of the register address to which it is mapped is as follows:

Group F0: 0x00; F1: 0x01; F2: 0x02; F3: 0x03; F4: 0x04; F5: 0x05; F6: 0x06; F7: 0x07; F8: 0x08; F9: 0x09; FA group: 0x0A, Fb group: 0x0B, FC group: 0x0C, Fd group: 0x0D, FE group: 0x0E, FF group: 0x0F, FH group: 0x10, FL group: 0x11, Fn group: 0x12, FP group: 0x13; FU group: 0x14; inverter control parameter group: 0x32; inverter status parameter group: 0x33.

For example, the register address of the inverter function code parameter F3.02 is 0x302, and the register address of the inverter function code parameter FF.01 is 0xF01.

5, the specific program is written: Start 5 # inverter forward rotation, speed is set to 50.00HZ (internal representation of 5000) command is as follows:

address

function code

Register address

Number of registers

Register contents bytes

Register contents

Checksum

request

0x05

0x10

0x3200

0x0002

0x04

0x01C7, 0x1388

0x16A9

response

0x05

0x10

0x3200

0x0002

no

no

0x4EF4

List of procedures:

Read the running frequency of 5# inverter, and the frequency inverter response running frequency is 50.00HZ:

address

function code

Register address

Number of registers or read bytes

Register contents

Checksum

request

0x05

0x03

0x3301

0x0001

no

0xDB0A

response

0x05

0x03

no

0x02

0x1388

0x44D2

List of procedures:

The 5# inverter stops at the fastest speed:

address

function code

Register address

Register contents

Checksum

request

0x05

0x06

0x3200

0x00C3

0xC6A7

response

0x05

0x06

0x3200

0x00C3

0xC6A7

Seventh, summary

The system was previously controlled using IPC+ control I/O cards. However, it has the disadvantages of poor system stability, unsatisfactory control results, and high failure rate. Since the use of EMERSON PLC as the core equipment of the system, the system has not only Achieve good control effect and very good economic benefits, at the same time easier to maintain, praised by users.

References: None

1 Emerson Corporation EV3000 Series Universal Inverter Emerson Network Power Co., Ltd.

3EC20 System Manual Emerson Network Power Co., Ltd.

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