Advantages and disadvantages of different output types of PLC – Mitsubishi

The three output types of PLC are: transistor output, thyristor output and relay output, what is the difference between these three different output types?

(1) Transistor output:

The big advantage is that it is accustomed to high-frequency action, and the response time is short, generally about 0.2ms, but it can only carry DC5-30V load, and the large output load current is 0.5A/point, but every 4 points shall not be greater than 0.8A.

(2) Thyristor output:

Only with load can be 0.2A/point, only with communication load, you can get used to high-frequency action, and the echo time is 1ms.

(3) Relay output:

The advantage is that different AC and DC loads can be carried between different common points, and the voltage can also be different, and the load current can reach 2A/point; However, the relay output mode is not suitable for high-frequency action loads, which is determined by the life of the relay. Its life is reduced with the increase of load current, generally between hundreds of thousands of times and Jl million times, and some companies' products can reach more than 10 million times, and the echo time is 10ms.

When the output frequency of your system is less than 6 times per minute, relay output should be preferred, because its circuit design is simple, anti-interference and load can be strong. When the frequency is less than 10 times/min, the relay output mode can be selected; PLC output can also be used to drive the Darlington triode (5-10A), and then drive the load, which can be greatly reduced.

ADVANTAGES OF TRANSISTOR: THE ACTION FREQUENCY CAN REACH HUNDREDS OF KHZ, NO CONTACT, SO THERE IS NO MECHANICAL LIFE;

Disadvantages: It can only be connected to DC load (generally below DC30V), and the current is relatively small;

Bidirectional thyristor (thyristor output): can only be connected to the load of communication, the action frequency is relatively high, the life is long, but the additional current of the load is also relatively small

Advantages of relay: both AC and DC loads can be driven; The extra current of the load is large;

Disadvantages: the frequency of action can not be too high, and the relay has a lifespan, generally 1 million times;

Advantages and disadvantages of different output types of PLC – Mitsubishi

Advantages and disadvantages of different output types of PLC – Mitsubishi

The transistor is primarily used for positioning and manipulation, and the output of the crystal is used to announce the pulse. The relay cannot be used to announce the pulse, so it cannot be positioned and controlled. If you use a relay to control the positioning servo or stepper, you need to add a positioning module, which is not cost-effective. With a transistor output, you can control the servo, etc. That's it. According to the requirements of the production process, the transistor output should be selected for the abortion of various indicator lights and inverters/digital DC governors, which are accustomed to high-frequency actions and have a short response time; If the output frequency of the PLC system is less than 6 times per minute, the relay output should be preferred, and the design of the output circuit is simple, and the anti-interference and load can be strong.

1. The transistor overload can be less than the relay overload

Generally speaking, when there is a large inrush current (e.g., bulb, inductive load, etc.), the transistor overload is less and the demand derating is more.

2. Transistors respond faster than relays

The principle of the relay output type is that the CPU drives the relay coil to make the contacts engage, so that the external power supply drives the external load through the closed contacts, and the open circuit leakage current is zero, and the response time is slow (about 10ms).

The principle of transistor output type is that the CPU is optically coupled to turn the transistor on and off to control the external DC load, and the response time is fast (about 0.2ms or even less). Transistor output is generally used for high-speed output, such as servo/stepper, etc., for output with high action frequency: such as temperature PID control, which is mainly used in stepper motor control, servo control, and solenoid valve control (valve action frequency is high).

3. The load voltage and current types are different

Load type: Transistors can only carry DC loads, while relays can carry both AC and DC loads.

Current: Transistor current 0.2A-0.3A, relay 2A.

Voltage: The transistor can be connected to DC 24V (generally the largest is about 30V DC, and the relay can be connected to DC 24V or AC 220V.)

4. The load can be different

The ability of a transistor with a load is smaller than that of a relay with a load, and when using a transistor, sometimes it is necessary to add other things to drive a large load (such as relays, solid-state relays, etc.).

5. In the case of additional operation, the relay has the life of the number of actions, and the transistor has no limit on the number of times of use as long as it is aged

Relays are mechanical components so they have a lifetime of action, and transistors are electronic components, as long as they are aged, there is no limit on the number of times they can be used. The number of switches per minute for relays is also constrained, while transistors are not.

6. The price of transistor output is slightly more expensive.

Advantages and disadvantages of different output types of PLC – Mitsubishi

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