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What are the precautions for the use of solid state relays?
Speaking of relays, we all know that it is an electrical control device, and this time we have to say solid state relays. So what is a solid state relay after all? What are the precautions for the use of solid state relays? Let's understand together. Solid state relay (SOLIDSTATERELAYS, hereinafter abbreviated as "SSR") is a new type of non-contact switching device composed of all solid state electronic components. It applies the switching characteristics of electronic components (such as switching triode, triac and other semiconductor devices) to connect and disconnect the circuit without contact and spark, so it is also called "non-contact switch". The solid state relay is a four-terminal active device, two of which are input control terminals and the other two are output controlled terminals. It has both amplification and isolation effects. It is suitable for driving high-power switch-type actuators. Compared with electromagnetic relays, it has higher reliability, no contact, long life, fast speed, and less interference to the outside world. Has been widely used.
When selecting solid state relays, we should analyze the corresponding conditions, research manuals, detailed standards and product technical performance and parameters. At the same time, we should note that the performance parameters and load of solid state relays can be greatly affected by ambient temperature and its own temperature. Its input has polarity request. When rational and capacitive loads are used, the output circuit is easily damaged by sharp seal voltage and surge current, power loss and heat dissipation caused by the on-state voltage drop. Focus on dealing with these problems, help to complete the scientific application of solid state relay, make it more reliable. Load type, output current and surge current: the steady-state current flowing through the output end of the solid state relay in operation shall not exceed the rated output current under the corresponding ambient temperature of the detailed standard of the product, and the surge current that may be presented shall not exceed the overload ability of the relay, and a certain margin is generally left. The bidirectional thyristor output is mostly used for resistive loads, and the unidirectional thyristor anti-parallel output is mostly used for rational and capacitive loads. Most loads can use the "zero control" type, but the demand for voltage regulation (such as dimming) and a few rational loads (such as transformers) must use the "random control" type.
There is almost no complete surge-free solid-state relay load, even if the electric heating elements, although they are purely resistive, due to the positive temperature coefficient, low temperature resistance is small, so it usually shows a large starting current. For example, the electric heating furnace switch-on current is often 1.3-1.4 times the steady-state current, and the incandescent lamp switch-on current is often 10 times the steady-state current. The wave and surge current of the halogen tungsten lamp can be as high as 25 times of the steady state value. The turn-on process of some metal halide lamps takes 10 minutes. During this process, the lamp and its ballast may be capacitive and rational. Current pulses up to 100 times the stable value may be accompanied.
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