Now there are many domestic manufacturers of electromagnetic relay, each factory has its own style, often make the purchaser dazzled do not know how to choose. So, choose a good electromagnetic relay need to pay attention to what? Today, we will take stock of what we should pay attention to when buying electromagnetic relays. When buying relays, we should pay attention to the use environment of the machine we will buy back, because different use environments have different effects on the instrument. For the contact requirements of the electromagnetic relay: small contact resistance, strong anti-arc ability, good wear resistance, long life, etc., in order to improve the relay contact life, the selection should pay attention to: A. The influence of mechanical environment on the contact point: The mechanical environment such as vibration and impact may cause the contact to misact, especially when the environmental vibration frequency is close to the natural frequency of the contact, the harm will be more significant. For example, the natural frequency of the ordinary reed relay is 800Hz, the natural frequency of the small reed relay is 2500Hz, and the natural frequency of the miniature reed is about 5000Hz. In order to prevent the external vibration frequency from resonating with the natural frequency, it is required that the external mechanical vibration frequency deviates from the natural frequency of the contact at least more than one time. 1B. The influence of humid environment on the contact: the contact of the relay is bound to produce an arc at the moment of power off and on, especially in the humid and harmful gas environment, which will accelerate the corrosion and oxidation of the contact. Because most of the oxides have semiconductor characteristics, the contact oxidation increases the contact resistance of the contact, and the increase of the contact temperature accelerates the contact oxidation, such a vicious cycle, and finally leads to contact failure. C. Impact of on-off effect on the contact point: The on-off effect of the contact point is not an ideal step function, especially when the contact is connected, it may produce many subtle on-off effects due to shaking, and this backjump is a very irregular temporary closure and disconnection phenomenon. A jump back process may have one break point, or there may be more than one break point, for high-speed digital circuits in the pulse circuit will occur abnormal action. Therefore, when choosing electromagnetic relay, we should pay attention to prevent the influence of this phenomenon. Mercury wet reed relay will not produce shiver, can overcome the shortcomings of electromagnetic relay. D. Low electrical level failure of the contact: when the contact voltage of the relay is less than 50mV or the contact current is less than 10mA, low electrical level failure may occur.