Contacts are one of the most important components of electromagnetic relays. Contact performance is affected by factors such as contact material, contact pressure, load type, operating frequency, atmospheric environment, contact configuration and runout. If any of these factors cannot meet the predetermined values, point contact problems such as electrochemical corrosion of metals between contacts, contact fusion welding, wear, rapid increase in contact resistance, etc., may occur. The rated load of the contact refers to the voltage and current that the electromagnetic relay allows to break, and the size of the load determines the size of the voltage and current that the electromagnetic relay can control. The electromagnetic relay cannot exceed these two values during use, otherwise it will easily cause damage to the relay contact.

There are three contact forms of contact, namely point contact, line contact and surface contact. As far as electromagnetic relays are concerned, the contact form of the contact is mostly point contact. Common electromagnetic relays on the market have one set of contacts, two sets of contacts and three sets of contacts. In order to ensure that the accidental failure of the contact itself due to quality problems is avoided to the greatest extent during the experiment, and to ensure that the contact contact pressure is detected in the maximum space as far as possible, the electromagnetic relay with one set of contacts and three sets of contacts is abandoned during the experiment, and the electromagnetic relay with two sets of contacts is selected.

In the energized state, when the dynamic and static contacts are out of contact, if the current of the broken circuit exceeds a certain value (different relay contact materials are different, and the rated current is different), or the voltage at both ends of the contact gap exceeds a certain value (different relay contact materials are different, and the rated voltage is different), an arc will occur in the contact gap. The arc is actually the discharge of gas between the contacts under a strong electric field, which produces high temperature and emits strong light and sparks. The existence of arc, not only burns the metal surface of the contact, reduces the life of the appliance, but also extends the breaking time of the circuit, and even causes relay contact failure, which will cause fire or gas accidents in serious cases. Therefore, in order to accurately detect the change law of contact pressure, it is necessary to ensure that during the experiment, the current broken by the electromagnetic relay and the voltage applied at both ends of the relay contact cannot exceed the rated value.