PLC control system design steps and precautions - Xinjie

1. Hardware purchase

At present, there are a large number of PLC products on the market, more and more cost-effective, and the optional fields are getting bigger and bigger.

1. At the beginning of the system scale, it should be determined that the system is controlled by PLC stand-alone, or by PLC collection and control, and the number of PLC input and output points should be calculated accordingly.

2. The load type is determined according to the load carried by the PLC output terminal is DC type or exchange type, whether it is a large current or a small current, and the frequency of the PLC output point action to determine the output terminal to choose the relay output, or the transistor output, or the load that does not match the output of the quality chasstor, which is the main thing for the constant work of the system.

3. Storage capacity and speed: Generally, the larger the storage capacity and the faster the speed of the PLC, the higher the price, we should not blindly seek large capacity and high speed when choosing, but should choose PLC products reasonably according to the size of the system.

4. Operation is a rigid policy of PLC operation. The automatic control system will get people out of the busy operation and the harshness, and the automatic control system is required to be able to adapt to the messy, such as temperature, humidity, music, signal barrier, operating voltage, etc., and it is necessary to select products that adapt to the actual operation.

5. After-sales service should try to choose the products of large companies, its quality is guaranteed, and the manual support is good, the general after-sales service is also better, and it is also beneficial to your product expansion and software promotion.

PLC control system design steps and precautions - Xinjie

PLC control system design steps and precautions - Xinjie

2. Enter the items to be aware of back to your imagination:

1. The power supply back to the PLC power supply is generally AC85-240V (there are also DC24V), which is suitable for a wide range of power supply fields, but in order to resist interference, power purification components (such as power filter 1:1 barrier transformer, etc.) should be installed.

2. The use of DC24V power supply on PLC companies generally has DC24V power supply on PLC products, but the power supply capacity is small, tens of milliamperes to hundreds of milliamperes.

3. If the use of external DC24V power supply is input back to the DC24V power supply near switch photoelectric switch, etc., and the DC24V power supply capacity on the PLC is insufficient, the DC24V power supply should be supplied from the outside, but the -end of the power supply should not be connected with the DC24V -end and the COM end of the PLC, otherwise the work of the PLC will be affected.

4. When the input voltage and current are less than the voltage and current of the transmission terminal of the PLC of each manufacturer, if there is a diode or resistance in the input return series (not enough to start completely), or there may be parallel resistance or leakage current (not enough to completely block), there will be a malfunction, and the degree of activity will decrease, and the method should be used for this. When the input current of the input device is greater than the maximum input current of the PLC, it will also cause malfunction, so the input device with weak current should be selected, and the PLC with the input as a common drain type input should be selected.

3. Notes on the output back to the imagination:

1. Output compilation selection

(1) Relay output: the interest can be incompatible AC and DC loads between incompatible common points, and the voltage can also be incompatible, and the load current can reach 2A points; However, the relay output is not suitable for the load of high-frequency action, which is determined by the life of the relay (2) Thyristor output: with a load capacity of 0.2A/point, can only be with exchange load, can adapt to high-frequency action, the response time is 1ms (3) Transistor output: the maximum benefit is to adapt to high-frequency action, the response time is short, generally 0.2ms domination, but it can only be with DC5-30V load, the maximum output load current is 0.5A/point, but every 4 points shall not be greater than 0.8A. When the output frequency of your system is less than 6 times per minute, the relay output should be preferred, because of its simple electrical image, anti-interference and strong load capacity, when the frequency is less than 10 times/min, you can choose to use the relay output program, or you can choose the PLC output to drive the Darlington triode (5-10A), and then drive the load.

PLC control system design steps and precautions - Xinjie

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