Photocoupler

The elements of climate stress mainly refer to factors such as temperature, humidity, atmospheric pressure (altitude), coastal atmosphere (salt fog corrosion), sand dust pollution, chemical gas and electromagnetic interference. Considering the universal applicability of the system in various industries and natural environments throughout the country, taking into account the special nature of reliable operation for many years, the key parts of the system must be fully sealed with high insulation and strong electrical resistance (metal cover seal or plastic seal type, metal The hood sealing product is superior to the plastic sealing product) relay product. Because only fully sealed relays have excellent long-term tolerance to harsh environmental performance, good electrical contact stability, reliability and stable switching load capacity (not affected by external climate).
1. The influence of temperature on the relay is afraid of the heat element. The high temperature can accelerate the aging of the plastic and insulating materials inside the relay, the oxidation corrosion of the contact, the difficulty of arc extinguishing, the deterioration of the electrical parameters, and the reliability is reduced. Therefore, the relay is required to be designed. Do not get close to the heating element and have good ventilation and heat dissipation conditions. Although the relay is afraid of thermal components, it can not be ignored for low temperature (such as military aviation conditions -55 °C). The low temperature can make the contact cold adhesion increase, the contact surface is exposed, and the surface of the armature produces ice film, making the contact Can not be converted normally, especially small power relays are more serious. The test proves that for some domestic small-power relays produced according to the standard, although the conditions are as low as -55 °C, the relay can not be normally converted under these conditions. It is recommended to leave sufficient margin when selecting. For important military electronic machines, it is recommended to use the national military standard products.
2, the effect of low air pressure on the relay Under low air pressure conditions, the relay heat dissipation condition becomes worse, the coil temperature rises, the relay's given pull-in and release parameters change, affecting the normal operation of the relay; the low pressure can also make the relay The insulation resistance is lowered, the contact arc extinguishing is difficult, and the contact is easily melted, which affects the reliability of the relay. For the harsh environment, it is recommended to use the whole machine seal.
3. The influence of mechanical stress on the relay mainly refers to the stress acting elements such as vibration, impact and collision. The main considerations for the control system are the anti-seismic stress and the ability to resist mechanical stress. A small intermediate relay with a balanced armature mechanism should be selected. The reeds of the electromagnetic relay are all cantilever structure, the natural frequency is low, vibration and shock can cause resonance, resulting in the pressure drop of the relay contact, which is prone to instantaneous disconnection or jitter of the contacts. In severe cases, structural damage can occur, and the movable armature Some can cause malfunction and affect the reliability of the relay. It is recommended to take anti-vibration measures in the design to prevent resonance.
According to the influence of the above environmental conditions on the relay, when selecting the relay, the relay must first meet the requirements of the various environmental conditions specified by the whole machine. If the environmental conditions cannot be fully considered, the complete machine developed will not meet the technical requirements stipulated in the contract. For example, JRC-5M small electromagnetic relay is selected on military airborne electronic equipment. If only the ambient temperature is attached, the requirements of the whole machine can be met and the vibration and impact conditions are neglected. If these conditions are not met, appropriate precautions must be taken, otherwise reliability will not be guaranteed.
4. The exposed insulator of the insulated endurance non-sealed or sealed relay is exposed to dust and water vapor for a long time, which causes the insulation strength to decrease. Under the overvoltage of switching the inductive load, the insulation breakdown failure is caused. For the inherent characteristics of relay insulation, the following technical characteristics of the relay must be selected in the selection:
4.1 Adequate creepage distance: general requirements > 3 mm (working AC 220V);
4.2 Sufficient insulation strength: between the conductors without electrical connection >AC2000 V (working AC220V), between the same group of contacts >AC1000 V;
4.3 Sufficient load capacity: DC 220 V inductive; 5~40ms, >50W; 2.4.4. Long-term ability to withstand climate stress: coil anti-mildew, insulation and anti-electricity level is stable and reliable for a long time.