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The difference between relays and intermediate relays

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Relays and intermediate relays are a kind of electronic components, intermediate relays are generally used to expand the use of current, auxiliary relays are generally used to increase the contact, the basic principle of the two is the same, in the requirements of the less stringent can be close to common. So the following is a detailed description of the differences between relays and intermediate relays.


The difference between relays and intermediate relays


1、Different concepts


Intermediate relay

Intermediate relays are used in relay protection and automatic control systems to increase the number and capacity of contacts. It is used to transmit intermediate signals in the control circuit.


Auxiliary Relay

Auxiliary relays are implemented with software, they cannot receive external input signals, nor can they directly drive external loads, they are an internal state flag, equivalent to intermediate relays in relay control systems.


2、Different structures


Intermediate relays

(1) The coil is mounted on a "U" shaped magnetic conductor, with a movable armature on top of the conductor, and two rows of contact shrapnel on both sides of the conductor. In the non-action state contact shrapnel will armature upward, so that the armature and the magnetic body to maintain a certain gap between. When the electromagnetic torque between the air gap exceeds the reaction torque, the armature is sucked into the guide magnet, while the armature presses the contact shrapnel, so that the normally closed contacts off normally open contacts closed, complete the relay work. When the electromagnetic torque decreases to a certain value, the contact and armature return to the initial position due to the reaction torque of the contact shrapnel, ready for the next work.


(2) The "U" shaped magnetic conductor of this relay has a double core structure, i.e. the coil can be installed on both side columns. For DZY, DZL and DZJ types, only one coil is installed, while for DZB, DZS and DZK types, the other core can be equipped with a holding coil or a damping piece for time delay, etc., as required. This allows relays with very different coil types to have a common conductor.


(3) The principle of intermediate relays and AC contactors are the same, are composed of fixed core, dynamic core, spring, dynamic contact, static contact, coil, terminals and housing.

Auxiliary Relays


There are many auxiliary relays in PLC, they can not receive external input signals, and can not directly drive the external load, in the PLC internal only play a role in the transmission of signals, not in contact with the external PLC, is a kind of internal state sign, the role is equivalent to the relay control system in the intermediate relay.


3、Different classification


Intermediate relay

(1) Static type

Static intermediate relays are used in various protection and automatic control circuits. These relays are composed of electronic components and precision small relays, etc. They are the preferred products for the renewal of power series intermediate relays.


(2) Electromagnetic type

When the excitation applied to the relay coil is equal to or greater than its action value, the armature is sucked into the guide magnet, and at the same time the armature presses the contact shrapnel, making the contact turn on, off or switch the circuit being controlled. When the relay coil is de-energized or the excitation amount is reduced to less than its return value, the armature and contact plate return to their original position.


2、Auxiliary Relay


(1) General Auxiliary Relay The general auxiliary relay of FX series PLC has no power failure protection function. In FX series PLC, except for the component number of input relay and output relay which are in octal, the component number of other programmed components are in decimal.


(2) Battery backup/latch auxiliary relays 

Some control systems require to memorize the state of the moment of power interruption and reproduce the state after re-energizing, battery backup/latch auxiliary relays can be used for this purpose.


(3) Special Auxiliary Relays

Special auxiliary relays totaling 256 points, they are used to indicate certain states of the PLC, provide clock pulses and flags (such as in, debit flags), set the operation of the PLC, or for step-by-step control, prohibit interrupt, set the counter is to add or subtract count, etc..

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