( 1 ) Discriminant type ( AC or DC ) electromagnetic relay is divided into AC and DC, which must be distinguished in use.
Because the alternating current continuously assumes the sine change, when the current passes through the zero value, the suction of the electromagnet is zero, and then the armature will be released; with the constant change of alternating current, the armature will constantly be inhaled and released, which is bound to produce violent vibration. To prevent this from happening, a copper short-circuit ring is installed at the top of the core. The function of the short circuit ring is that when the alternating flux passes through the short circuit ring, the induced current is generated, which prevents the original magnetic field from vanishing when the alternating current passes through zero, a certain amount of suction is maintained between the armature and the yoke, thus eliminating the vibration at work. In addition, the words " AC " are often marked on the coil of the AC relay. The DC electromagnetic relay has no copper ring and is marked " DC " on the DC relay. Some relays are marked with AC / DC and are used correctly according to the nominal voltage.
( 2 ) The measuring coil resistance is based on the nominal DC resistance value of the relay, and the multimeter is placed in an appropriate electrical barrier, and the resistance value of the relay coil can be directly measured. The two stylus will be connected to the two pins of the relay coil, and the multimeter indicates that they should basically meet the nominal DC resistance of the relay.
(3)The number and category of the discriminant contacts are marked with contact and pin function diagram on the relay housing, which can be directly identified. if no annotated, the relay shell can be dismantled and the relay's contact structureis carefully observed, and the relay has several pairs of contacts, the type of each pair of contacts and which reed constitute a trigger end corresponding to a set of contacts.
(4)Check the armature work situation with the hand to move the armature, see whether the armature activity is clever, there is no card phenomenon. If the armature activity is blocked, we should find out the reason to eliminate.
In addition, you can press the armature by hand, then let go to see if the armature can return to the original position under the action of spring (or reed). Note that the return spring is easier to rust and should be used as a key inspection area.
(5)When the relay produces a sucking action, the voltage at both ends of the coil is gradually reduced, and the current readings on the table will slowly decrease. When the value is reduced to a certain value, the original armature will be released, and the data is the release voltage and the release current. The release voltage of a general relay is 10%~50% of the pull in voltage. If the release voltage of the tested relay is less than the 1/10 suction voltage, the relay should not be used any longer.
( 6 ) Measurement of contact resistance
The resistance of the normally closed contact is first measured with a multimeter RX1 block, and the resistance should be zero. Then measure the resistance of the normally open contact, the resistance should be infinite. Then press the armature, when the normally open contact is closed, the resistance becomes zero; normally closed contacts turn on, and the resistance becomes infinite. If the static and dynamic contact is not changed properly, the corresponding reed can be gently moved to make it fully closed or open. The relay can no longer be used if the contact resistance is great or the contact has melted after the contact is closed. If the contact resistance is large and unstable after the contact is closed, the contact point is intact, but the surface color is black, and then the fine sand paper is applied to wipe the contact surface, make it come in good contact.
( 7 ) It is estimated that the contact load of the relay should be known exactly, and the relevant manual or information should be consulted, but sometimes it can be estimated by experience. Generally, the relay with large contact points, armature and powerful, simple and large size relays, has a relatively large contact load. Note that in several of the above measurements, DC should be used to test DC relays. If the AC relay is measured, then the AC power supply should be used, and the corresponding multimeter should also use AC 50mA blocking circuit.