Solid state device is used for contactless communication of devices. With each passing day the popularity of this relay is increasing, and today it is ready to displace from the market electromagnetic contactors.
Operating Principle and Design
Solid state relays allow the interconnection of high and low voltage circuits.
Most solid state relay devices have a common concept with various additions and modifications which do not affect the operating principle.
What is a solid state relay? It is a device consisting of the following elements:
- An input node;
- An optical isolation system;
- A trigger circuit;
- switch;
- protection.
A primary circuit with a resistor is used as the input. The connection is serial. The task of the input circuit is to receive the signal and transmit the command to the switch.
The input and output circuit is isolated by an optical isolation device. Its type determines the operating principle and the type of relay.
The trigger circuit processes the input signal and switches the output. Depending on the contactor model, it can be part of the optical isolation or an independent element.
A switch circuit is used to apply the voltage. This operation involves a triac, a silicon diode and a transistor.
The protection circuit is necessary to prevent errors and other malfunctions. It can be external or internal.
The principle of the solid state relay is the closing and opening of the switching contacts that transmit the voltage to the device. In order for the contacts to start working, an activator is required. This task is performed by a solid state device. Dc devices use a transistor, while dc devices use a triac or thyristor.
Every device that has a key transistor is a solid state contactor. As an example, consider a light sensor that transmits voltage using a transistor.
The optical circuit neutralizes the galvanic effect that results from the voltage between the contacts and the coil.
Applications
Standard contactors are gradually leaving the market, giving way to solid-state equipment. This is due to a number of advantages of the new product:
- Low electricity consumption. The semiconductor in the TTR used consumes 90% less energy than its electromagnetic counterpart.
- Small size of the device, facilitating transportation and installation.
- Does not need to wait for start-up and has high speed performance.
- Low noise level.
- Long service life. No ongoing maintenance required.
- Broad field of application and compatibility with many devices.
- No electromagnetic interference.
- More than one billion actuations.
- Improved isolation between switching and input circuitry.
- Resistant to vibration and shock.
- Hermetically sealed.
Use solid state contactor if inductive load is to be switched. Main applications:
- In electric heater temperature control systems;
- Maintaining the temperature level in the process;
- in the control circuit;
- control of temperature readings of technical devices and equipment;
- regulation and control of lighting.
Types of RTDs
These devices are of many kinds. They differ in the way of commutation and voltage control:
- Solid state DC relays are used for connection to a network with constant electricity. The voltage range can range from 3 to 32 watts. The TTR is highly reliable and can have an LED indication. It operates at ambient temperatures ranging from -30°C to +70°C.
- AC contactor does not produce noise, is fast and low power consumption. Voltage range is 90-250 W.
- TTR with manual control. In this device, you can set the type of operation yourself.
In addition, there are single-phase and three-phase relays.
The first relay can connect circuits in the range of 10 to 120 A or 100 to 500 A. The switching is done by means of a resistor and an analog signal. In the second case the switching is carried out simultaneously on 3 phases with a working interval of 10 to 120 A. Three-phase contactors are of the reversing type. Their difference is the contactless communication and special marking. Such devices have reliable protection against false switching.
Three-phase TTR is necessary for the start and correct operation of the asynchronous motor. In order to operate this device safely, it is important to maintain a voltage reserve.
Overvoltage can occur during the operation of the solid state AC relay. A fuse or varistor must be used to protect the unit.
The three-phase device has a longer service life due to zero-switching as well as the LED indication.
In addition to the method of communication, the devices differ in:
- weak induction and capacitive type load;
- Switching method (random or instantaneous);
- the presence of phase control.
The device has design differences:
- universal - the design allows the relays to be mounted on adapter strips;
- mounted on DIN-rails.
Purchase this product should be in specialized stores, where specialists can help with the selection of the required type and advise how to connect the device. The device may differ:
- mounting method;
- housing material;
- additional functions;
- performance level;
- dimensions and other parameters.
Important: Installed relay must have several times more power reserve than used device. Failure to comply with this condition can lead to instantaneous failure of the RTD. You can protect the device from overvoltage by installing a fuse.
The contactor heats up quickly. This leads to a significant loss of performance. When heated above 65°C the device can burn out. Only use the device with a cooling heatsink is allowed. The current reserve should be higher by a factor of 3. When working with asynchronous motors, the reserve is increased by a factor of 10.
How to connect the relay
To connect the relay yourself, you need to consider the following nuances:
- connections are fastened with screws, soldering is not used;
- Do not allow metal dust and chips to get inside the device;
- Do not allow the body of the device to come in contact with foreign objects;
- do not touch the device during its operation (you can get burnt);
- do not place TTR near flammable objects;
- it is necessary to check the wiring diagram of the solid-state relay;
- When the case heating above +60 ° C requires the installation of a heat sink.
Related articles:Important! Short-circuiting the output of the device can cause instantaneous damage. The solid state relay must be controlled according to the manual.
