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Relays

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Current monitoring relay Siemens 3RR22421FA30 Screw connection AC/DC
Special offer

Current monitoring relay Siemens 3RR22421FA30 Screw connection AC/DC

€106.71 +VAT
PLN 501.23
  • Manufacturer: Siemens
  • Manufacturer Code: 3RR22421FA30
  • EAN: 4011209787292
  • Type of electric connection: Screw connection
  • Voltage type for actuating: AC/DC
  • Min. adjustable delay-on energization time [s]: 0
  • Max. permitted delay-on energization time [s]: 99
  • Min. adjustable off-delay time [s]: 0
Supplier:
EL
Response time: usually up to 1 day
Temperature monitoring relay Siemens 3RS10001CD20 Screw connection AC/DC
Special offer

Temperature monitoring relay Siemens 3RS10001CD20 Screw connection AC/DC

€86.13 +VAT
PLN 404.57
  • Manufacturer: Siemens
  • Manufacturer Code: 3RS10001CD20
  • EAN: 4011209535268
  • Type of electric connection: Screw connection
  • Voltage type for actuating: AC/DC
  • Number of measuring circuits: 1
  • Number of contacts as normally closed contact: 1
  • Number of contacts as normally open contact: 1
Supplier:
EL
Response time: usually up to 1 day
Timer relay Siemens 3RP15111AP30 Screw connection AC/DC
Special offer

Timer relay Siemens 3RP15111AP30 Screw connection AC/DC

€54.20 +VAT
PLN 254.55
  • Manufacturer: Siemens
  • Manufacturer Code: 3RP15111AP30
  • EAN: 4011209318700
  • Type of electric connection: Screw connection
  • Voltage type for actuating: AC/DC
  • Number of outputs, undelayed, normally closed contact: 0
  • Number of outputs, undelayed, normally open contact: 0
  • Number of outputs, undelayed, change-over contact: 0
Supplier:
EL
Response time: usually up to 1 day
Timer relay Siemens 3RP25051BW30 Screw connection AC/DC
Special offer

Timer relay Siemens 3RP25051BW30 Screw connection AC/DC

€75.63 +VAT
PLN 355.24
  • Manufacturer: Siemens
  • Manufacturer Code: 3RP25051BW30
  • EAN: 4011209943513
  • Type of electric connection: Screw connection
  • Voltage type for actuating: AC/DC
  • Number of outputs, undelayed, normally closed contact: 0
  • Number of outputs, undelayed, normally open contact: 0
  • Number of outputs, undelayed, change-over contact: 0
Supplier:
EL
Response time: usually up to 1 day
Timer relay Siemens 3RP15552AR30 Spring clamp connection AC/DC
Special offer

Timer relay Siemens 3RP15552AR30 Spring clamp connection AC/DC

€136.13 +VAT
PLN 639.40
  • Manufacturer: Siemens
  • Manufacturer Code: 3RP15552AR30
  • EAN: 4011209445192
  • Type of electric connection: Spring clamp connection
  • Voltage type for actuating: AC/DC
  • Number of outputs, undelayed, normally closed contact: 0
  • Number of outputs, undelayed, normally open contact: 0
  • Number of outputs, undelayed, change-over contact: 0
Supplier:
EL
Response time: usually up to 1 day
Temperature monitoring relay Siemens 3RS10101CD00 Screw connection AC/DC
Special offer

Temperature monitoring relay Siemens 3RS10101CD00 Screw connection AC/DC

€86.13 +VAT
PLN 404.57
  • Manufacturer: Siemens
  • Manufacturer Code: 3RS10101CD00
  • EAN: 4011209535305
  • Type of electric connection: Screw connection
  • Voltage type for actuating: AC/DC
  • Number of measuring circuits: 1
  • Number of contacts as normally closed contact: 1
  • Number of contacts as normally open contact: 1
Supplier:
EL
Response time: usually up to 1 day
Timer relay Siemens 3RP15742NM20 Spring clamp connection AC
Special offer

Timer relay Siemens 3RP15742NM20 Spring clamp connection AC

€77.31 +VAT
PLN 363.11
  • Manufacturer: Siemens
  • Manufacturer Code: 3RP15742NM20
  • EAN: 4011209645769
  • Type of electric connection: Spring clamp connection
  • Voltage type for actuating: AC
  • Number of outputs, undelayed, normally closed contact: 0
  • Number of outputs, undelayed, normally open contact: 1
  • Number of outputs, undelayed, change-over contact: 0
Supplier:
EL
Response time: usually up to 1 day
Timer relay Siemens 3RP15121AQ30 Screw connection AC/DC
Special offer

Timer relay Siemens 3RP15121AQ30 Screw connection AC/DC

€54.20 +VAT
PLN 254.55
  • Manufacturer: Siemens
  • Manufacturer Code: 3RP15121AQ30
  • EAN: 4011209318731
  • Type of electric connection: Screw connection
  • Voltage type for actuating: AC/DC
  • Number of outputs, undelayed, normally closed contact: 0
  • Number of outputs, undelayed, normally open contact: 0
  • Number of outputs, undelayed, change-over contact: 0
Supplier:
EL
Response time: usually up to 1 day
Timer relay Siemens 3RP15252AP30 Spring clamp connection AC/DC
Special offer

Timer relay Siemens 3RP15252AP30 Spring clamp connection AC/DC

€71.42 +VAT
PLN 335.46
  • Manufacturer: Siemens
  • Manufacturer Code: 3RP15252AP30
  • EAN: 4011209444942
  • Type of electric connection: Spring clamp connection
  • Voltage type for actuating: AC/DC
  • Number of outputs, undelayed, normally closed contact: 0
  • Number of outputs, undelayed, normally open contact: 0
  • Number of outputs, undelayed, change-over contact: 0
Supplier:
EL
Response time: usually up to 1 day
Temperature monitoring relay Siemens 3RS11211DW30 Screw connection AC/DC
Special offer

Temperature monitoring relay Siemens 3RS11211DW30 Screw connection AC/DC

€144.94 +VAT
PLN 680.80
  • Manufacturer: Siemens
  • Manufacturer Code: 3RS11211DW30
  • EAN: 4011209535916
  • Type of electric connection: Screw connection
  • Voltage type for actuating: AC/DC
  • Number of measuring circuits: 1
  • Number of contacts as normally closed contact: 0
  • Number of contacts as normally open contact: 1
Supplier:
EL
Response time: usually up to 1 day
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Relays

A relay is an electrical or electronic device designed so that a change in a specified physical quantity (e.g., current, voltage, or temperature) at its input causes a step change in its output signal. In general, the role of a relay is to open and close an electrical circuit.

Relays

A whole large group of relay devices can be divided in various ways, depending on the criterion adopted. Depending on the type of application, we can distinguish industrial relays, installation relays, miniature relays or safety relays. The main division, however, is a classification based on construction, into electromagnetic relays and solid-state relays.

Relay functions - galvanic separation and switching

The relay is divided into an input section and an output section and has two basic roles in control systems:

  • switching of high power loads and high current and/or high voltage at the expense of low power consumption (low voltage/low current signal).

  • galvanic separation of the control section from the switching section. Galvanic separation involves blocking the direct flow of current while maintaining the ability to exchange energy and information. The low-power control circuit is galvanically isolated from the high-power execution circuit, so that the controller's inputs/outputs are protected from short circuits, switching errors and overvoltages on the load circuit side. Overvoltages may originate from the power network, but also take the form of peaks created by the disconnection of highly inductive circuits.

Electromagnetic relays

Electromagnetic relays are based on an electromagnet which, when a voltage is applied to the coil, closes (opens) the contacts and thus switches (disconnects) the load circuit.

How does an electromagnetic relay work?

An electromagnetic relay is made up of an electromagnet (coil, ferromagnetic core, yoke and ferromagnetic jumper) and additional elements, including contact springs and connectors. Application of input voltage to the coil creates an electromotive force moving the jumper. The movement of the jumper causes the contact to switch. If the contact is normally open, application of voltage results in shorting the contact. When the voltage is lost, a return spring pushes the contact away, as a result the contact opens and the load circuit is disconnected.

Selection Criteria for Electromagnetic Relays

When selecting an electromagnetic relay for specific operating conditions, a number of parameters of the device must be taken into account, among which the most important are

  • designation for direct current (DC) or alternating current (AC).

  • Power supply voltage of the coil. The rated coil voltage, or control voltage, is the voltage value for which the relay is designed and rated to operate. Manufacturers of devices specify in catalog cards (and usually also directly on the relay housing) the voltage range to which the coil is adapted. The most commonly used voltages for relay control are: 12, 24 and 48V DC and 24 and 230V AC.

  • rated current - relay load size expressed in amperes, i.e. the highest current that can be continuously carried by the contacts of the device.

  • type and number of contacts. A contact is the actuating element of a relay. There are:

    • normally-open contacts, i.e. normally-open contacts, denoted by the symbols Z, NO, SPST-NO,

    • normally closed contacts, denoted by symbols R, NC, SPST-NC,

    • changeover contacts designated by symbols P, CO, SPDT, DPDT.

Additionally, the number of contacts is important. There are single-contact relays (with one changeover contact) and multi-contact relays (with two or four contacts).

Solid-state relays

Solid-state relays (SSRs) use a so-called optocoupler (optoisolator) to separate the input and output circuits, which contains a transmitter (usually an LED) and a receiver (e.g. a phototransistor). For galvanic isolation a physical gap between transmitter and receiver must be maintained. The optocoupler is also responsible for driving the power circuit.

How does a solid state relay work? An electrical control signal is given to the input of the circuit, which reaches the optocoupler, where it is converted into an optical signal (light). The optocoupler consists of an electrically isolated and optically coupled transmitter-receiver pair in a common housing that is impervious to light. The optical signal for the switching operation is triggered by a photoconductor, usually a gallium arsenide light-emitting diode (LED) emitting infrared light and transmitted inside the optocoupler housing. Reaching receiver (photoresistor, photodiode, phototransistor, phototriac), it causes switching of contacts.

An optocoupler is a unilateral element, which means that it allows only one direction of signal flow from the input circuit with photoemitter to the output circuit with photodetector.

Characteristics of electromagnetic and solid-state relays

Compared to electromagnetic relays, solid-state devices have many advantages:

  • durability and reliability,

  • fast operation,

  • high resistance to vibrations, shocks and contamination of the working environment,

  • no moving parts, which translates into silent operation (important in offices, living quarters etc.)

  • no electric arc (galvanic break between the photon transmitter and photodetector),

  • ability to switch on high starting currents,

  • no electromagnetic interference thanks to fully electronic control.

Unfortunately, solid-state relays are not free from disadvantages, which include, above all, large voltage drop at the terminal, sensitivity to overvoltage and high resistance in the on-state. The latter feature results in considerable heat generation and the need for a heat sink.

In systems where these features are important, it is recommended to use electromagnetic relays, which are characterized by a small voltage drop (in the ON state, the contact transition resistance is usually about 10 mΩ), zero leakage current and significant resistance to overvoltage. Compared to solid-state relays, electromagnetic relays have a small service life due to mechanical switching of contacts, they are also noisy, their response time is long and they are much less capable of switching surge currents.