Relay and Optocoupler Applications

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Interesting Fact and Applications

Relays with Ex Approval

Fast and flexible: Relays from WAGO are suitable for use in Zone 2 explosive atmospheres and thus cover a wide range of applications.

Hazardous Areas

Potentially explosive areas arise in various applications including the chemical industry, during the production of crude oil or natural gas and in the food industry. These are divided into Zones 0, 1 and 2 according to the frequency and duration of occurrence of potentially explosive atmospheres. Relays from WAGO are suitable for use in Zone 2 explosive atmospheres.

Relays with Ex Approval (Zone 2)

Labeling devices that may be used in potentially explosive areas is mandatory.

In order to reduce costs but still be able to install the products in the Ex area, facility operators try to use devices with Zone 2 approval.

A type examination certificate or manufacturer’s declaration is required for use in potentially explosive areas. You can download these from the eShop and add them to your system documentation.

Zone 2

Area in which it is not anticipated during normal operation that a potentially explosive atmosphere will occur as a mixture of flammable materials in the form of gas, vapor or mist with air. If one does occur, then only momentarily.

Relays for Systems with Long Lines

Reliable switching despite coupling: To switch on, relay modules require nominal voltage U_N. For operation, however, a holding voltage that’s just 15 % of the nominal voltage is sufficient. In standard circuits, all relay modules operate reliably. However, in circuits with long parallel lines, or those with either active two-wire sensors or digital AC control outputs, a low holding voltage often leads to malfunction. The modules no longer switch off.

This effect often occurs when updating systems, changing old “power-hungry” to current “power-saving” relay modules.

What are the causes and how can they be eliminated?

Long parallel lines are capacitively coupled to each other. Energy is then transferred to an adjacent conductor. Active two-wire sensors, such as proximity sensors or level monitors, normally require a minimum continuous current to ensure that the holding voltage is maintained on the relay control lines. Because of this behavior, the relay cannot switch correctly.

For such applications, WAGO has developed specific RC base load modules to protect against interference coupling and integrated them into the relay modules. These modules minimize the unwanted voltages at low loss and allow defined switching.

Relay Selection with Integrated Base Load Module

Lighting Systems and Relays

Brief power spikes, fatal consequences: When equipped with electronic control gears (ECGs) or LED drivers, modern lighting systems offer numerous advantages. They generate flicker-free light with high levels of efficiency. Both in planning new lighting system and replacing old ones, the inrush current of the ECGs is a central concern.

A capacitor in the input circuit of many ECGs and LED drivers causes a substantial current peak when switched on that can far exceed ten times the rated current. Even if the current lasts for just a few milliseconds, it can cause the relay contacts to fuse.

What should be considered when planning lighting systems?

When selecting relays, the inrush current must be considered. Standard relays quickly reach their limits. For such applications, WAGO has developed relay modules with contacts that safely withstand brief high-peak inrush currents. The contact material reliably prevents contacts from catching or fusing.

For maximum inrush currents, relay modules with two contacts working in parallel are available. The first contact, consisting of high-strength tungsten, catches the current peak. The second contact, made of highly conductive silver alloy, manages the operational current.

As an alternative to relays, the WAGO product portfolio includes optocouplers and solid-state relays for use with capacitive loads. Special designs with zero voltage switches minimize the peaks.

Relays for Lamp Loads