relay symbol

Relay symbol

Below you can find a complete list of the most commonly used types of relays, divided into four sections, Measurement relays, Control relays, Contacts and Relay coil, and finally Electromagnets and Controls, together with a simple description of their function, way of work and use in industrial automation.

If you wish, make “click” on the symbol of each relay to go to our download page and there download free CAD.dwg file of each type of relay to use it directly in the designs and schemes of your projects

Relay symbol – Measuring relays

Low power or synchrony relay

It is used to open or close an auxiliary or secondary circuit depending on whether the intensity or power of the circuit being controlled is kept within the range of a predetermined value and does not fall below said value, they are known as synchronization relays since ensure that there is synchrony to connect two sections of a circuit

Low power or synchrony relay

Low impedance relay

In this case, the adjustment of the relay is achieved by varying the number of turns of the coil so that the torque on the contact head and the opposite pair exerted by the spring are balanced at the moment that the quotient between voltage and current applied to the relay is equal to the adjustment impedance

Low impedance relay

Reverse current relay

The current or reverse power relay is sensitive to the direction of current flow, and is used in systems in which several electric generators are synchronized.

This relay acts by analyzing the inverse power of the load that we want to control, so that when one of the generators placed in parallel with other generators, is not generating the system, but is consuming energy from the other generators the relay is reversed and sends a signal to the synchronization control box of the generators so that the generator that is consuming energy from the system is disconnected

Reverse current relay

Maximum and minimum current relay

These relays are used to control the current flowing through a circuit, so that the relay changes from rest to excitation whenever the current flowing through the circuit to be controlled is out of a fixed range of minimum and maximum intensity .

See example of Hall effect current sensor

When the relay is excited in these circumstances, a contact is closed that can be used in another auxiliary circuit to activate an alarm signal.

Thus, when the maximum intensity is being controlled, the relay remains energized until the current to be controlled is lower than the set value. In the case of minimum current control, the relay remains activated until the intensity of the current to be measured is greater than the threshold value, returning to a value within the set range.

The normal thing is that the relay is de-excited with a few milliseconds of delay to prevent oscillations that do not wish to control as they would lead to false excitations. This delay can be varied and adjusted at will by acting on a potentiometer arranged for that purpose.

The hysteresis can also be controlled by another potentiometer to maintain it in ranges from 1 to 45% of the maximum and minimum intensity ranges set in the control.

Maximum and minimum current relay

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