Delta PLC's application in screw air compressor

1. Design intent  

For cost reasons, the control systems used in the air compressor manufacturing industry for a long time have been controlled by single-chip microcomputers, and digital tubes indicate working status and indicate parameter values. Although the system has a low manufacturing cost, it is difficult to cope with its own vulnerabilities such as being vulnerable to interference, modifying process procedures and inconvenient function expansion, and a series of challenges raised by customers. In addition, the unbalanced and intermittent use of gas in the production process and time period of the factory causes great fluctuations in gas consumption. If the peak gas consumption is used to plan the gas supply system, you will have to face the use of high-power motors through no-load and The capacity is adjusted to adapt to the huge energy waste caused by the air supply. Using PLC and man-machine interface will easily complete all the functions performed by the microcontroller and solve the problems faced by users with different needs.

2. Hardware architecture

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Figure 1 Network architecture diagram

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Figure 2 PLC wiring diagram

DP210, PWS3760: functional operation; information display; information query;

DVP14ES00R: Provide communication interface, perform data and logic processing, and perform joint debugging program tasks;

DVP20EX00R: Provide communication interface, perform data and logic processing, and perform stand-alone program tasks.

I/O allocation:

X0 reserved motor main contactor A0V+---A0V- temperature sampling

X1 temperature switch Y1 motor angular contactor A1I+----A1I- pressure sampling

X2 host overload Y2 motor star contactor D0I+----D0I- output 20mA constant value

X3 fan overload Y3 solenoid valve 

  X4 phase sequence error Y4 [cooling pump/fan] contactor  

X5 oil filter blocked Y5 buzzer  

X6 oil fine separator blocked    

  X7 air filter clogged     

Fourth, software design 

The software will be divided into two parts: PLC programming and man-machine interface design. 

PLC program design includes single-machine program design and multi-machine joint debugging program design: single-machine program design includes process actions (startup, air conditioning or ESC replacement, exhaust valve action and cooling system action judgment, etc.), alarm and alarm processing, and analog Sampling (temperature and pressure), screen replacement, communication and other parts of the design; the design of the joint debugging program is mainly based on the target pressure demand through the RS-485 communication port to handle the logic increase and decrease of multiple devices. 

 Interface design includes DP210 interface design and PWS3260 interface design:  

 DP210 interface: display stand-alone information and stand-alone operation/stop, mode change, fault query and reset, run/load time query, maintenance time prompt, user parameter setting and other operations. 

PWS3260 interface: in stand-alone operation mode, display the operating status and alarm information of each machine, remote start and stop, and authorized on-site operation settings; in online operation mode, display the deployment status of each machine and display the outlet pressure and temperature of each machine, fault query, reset, and operation / Load time query, maintenance time prompt, user parameter setting, authorized on-site operation setting, air supply pressure curve display and other operations.

Five, basic functions

1 Multi-mode operation:

 A Stand-alone automatic air conditioning/ESC operation: automatic replacement between air conditioning and ESC

 B Online automatic air conditioning operation: no ESC action 

C Manual air conditioning / ESC operation: manual replacement between air conditioning and ESC  

Air-regulated operation: In the light-load state (starting is prohibited in the heavy-load state), the motor is started by star-delta for 2 seconds, the solenoid valve is energized and the pressure reaches the set value, the solenoid valve is de-energized and disconnected, and the host continues to run . After the solenoid valve was continuously powered off for 20 minutes, the system entered the empty parking state for too long. When the pressure drops to the set lower limit, the system restarts, and the solenoid valve is loaded 2 seconds after the start is completed. Automatic state, three times in 90 minutes, the system will be automatically switched to the stand-alone automatic ESC operation state.  

ESC operation: In the light-load state (starting is prohibited in the heavy-load state), the motor is started by star-delta for 2 seconds, the solenoid valve is energized and the pressure reaches the set value, the solenoid valve is de-energized and disconnected, after 10 seconds The host stops, but if the pressure switch is closed within 10 seconds, the host will not stop. In the automatic state, the system will automatically switch to the automatic air control mode if the ESC runs 3 times within 30 minutes.

2 Parameter setting:  

  The upper and lower limits of the exhaust pressure: set by the user according to the gas consumption. The system presets the upper limit of 16Kg and the lower limit of 7Kg. It is allowed to modify the upper and lower limit interval to 0-16Kg, but when the lower limit is greater than the upper limit, the system forces the upper limit to be equal to the lower limit.

Fan start temperature and fan stop temperature: The default settings of the system are 75°C and 70°C respectively, and the upper limit of allowable modification is 85°C. 

  Maintenance time setting: including the whole machine maintenance time setting, oil filter maintenance time setting, oil fine separator maintenance time setting, and air filter maintenance time setting. All maintenance time settings are password-protected and set by the manufacturer, and user settings need to be authorized by the manufacturer. When the maintenance time of the whole machine arrives, the system is forcibly shut down, and it is prohibited to start until the manufacturer's commercial password is lifted; when the maintenance time for other parts is up, the user will remove the prompt and replace the parts.

3 Status display:

Exhaust pressure/exhaust temperature

No-load running time/load running time

Host status: host running/host stopped

Load status: load operation/no-load operation

Operation mode: stand-alone automatic air conditioning / ESC operation     

 Online operation   

   Manual air conditioning / ESC operation

Cooler status: fan [cooling pump] running/fan [cooling pump] stopped

Remaining maintenance time: remaining time for maintenance of the whole machine, remaining time for maintenance of oil filter, remaining time for maintenance of oil fine separator, remaining time for maintenance of air filter

4 Protection function:

A. Flashing displays various warning signals and records them for inquiry, including: phase sequence error (start prohibited); host overload (emergency shutdown); fan overload (emergency shutdown); host temperature is high (emergency shutdown); exhaust temperature is high (Emergency shutdown); pressure sensor failure (emergency shutdown); oil filter clogged (alarm); oil separator clogged (alarm); air filter clogged (alarm).

B. Dual temperature detection protection: In addition to using PT100 to detect the temperature of the exhaust port, an exhaust port temperature switch is also added to ensure the absolute safety of the system in the case of PT100 failure;

C. When the maintenance time of the whole machine arrives, the system is forced to stop and start is prohibited;

D. Add an emergency stop button to the control circuit for safety.

5 Query function: query the latest fault record, load running time, equipment running time, system maintenance time, pressure-time fluctuation curve.

Six, extended functions

Seven, multi-machine joint debugging: In order to meet the needs of customers at different levels, it is convenient for customers to configure the gas supply system at any time: it can not only meet the occasions of low gas consumption, but also meet the special needs of large fluctuations in gas consumption. This system adds the multi-machine joint debugging function, that is, as long as the customer sets the operating mode in the host computer to the multi-machine joint debugging mode, and at the same time enters the number of devices currently participating in the joint debugging on the user parameter setting screen, the system will follow the current The demand for gas consumption will automatically increase or decrease the number of equipment running to achieve reasonable gas supply and reduce operating costs.

7. Summary    The application of PLC and man-machine interface in the screw air compressor will easily replace the single-chip microcomputer and can do better.