Electromechanical or solid state relay? We can help you choose the right relay for your application Let’s connect. Relay applications Relay applications Electromechanical and solid state relays Selecting the most appropriate relay for an application is often met with confusion or even overlooked altogether. To address this issue we need to gain an understanding of the capabilities and limitations of each popular type of relay available to industry. Electromechanical relays The first relays were electromechanical, that is they comprised an electrical component, the coil and a mechanical component, the contacts. This type of relay is still by far the most common type in use today. The inherent simplicity and low cost has resulted in the electromechanical relay being used in many switching processes for inputs and outputs of control systems. Coil voltages are available for all industrial requirements from 5V DC to 240V AC. Contacts are typically available to switch up to 16A. Contacts can be arranged as normally open, normally closed or as a changeover, and in groups of 1 to 6 poles. In some cases electromechanical relays can be left to operate for many years without malfunction. The “Achilles Heel” of electromechanical relays is the fact that being partly mechanical they wear out, especially when they are required to switch at high speeds. High speed switching leads to deformation of the contact and overheating of the coil. Typical switching rates of more than a few operations per minute will require a more specialised product such as a Solid State Relay. Often when selecting a relay we only think about the maximum current and voltage a relay can switch. These are necessary but equally as important are the minimum switching values. As we will see the type of contact material and plating have a major influence on switching characteristics. Take for example the Weidmüller Termseries miniature rail mounted relays. These have contacts made of the alloy Nickel Silver. This is a very hard wearing material but is designed for minimum switching levels of at least 5 V at 100mA. The reason for this is that over time a thin layer of oxide or tarnish will develop on the face of the contacts. This is not a problem if the switching levels are above the minimum specified as the tarnish is removed by the small arc that is developed. If you were to switch a much smaller signal the contact resistance could be too great and the reliability of the switching action not maintained. 2 Termseries Riderseries To overcome this situation Weidmüller offers gold plated versions of their relay products. These versions use the same base contact material but with a plating of 5um of pure gold. This will allow signals down to 1V at 1mA to be reliably switched. For even smaller switching levels the MC5R Normally Open range of relays can switch down to 100mV at 100uA. These relays use a special bifurcated (two part) gold contact for the ultimate in low switching level reliability. WAUS Electromechanical and Solid state relays application brochure 2013 Solid state relays Input Coil + N/O Output _ Electromechanical diagram Some relays are produced with a gold flash over the base contact material. This is designed to give the contacts protection against airborne contaminants until such time that the relay is put into service. During switching operations the gold flash is usually burnt off leaving clean nickel silver contacts. The low level switching capabilities of gold flash contacts are therefore the same as nickel silver. Microopto Ever since the first industrial relays were produced there has been a concerted effort to overcome the deficiencies present in electromechanical relays ie. life constraints and switching frequency limitations. The invention of the Triac and the power MOSFET have enabled solid state relays to be developed and optimised for reliable industrial use. The coil and contacts have been replaced by an optical switch. In essence this is simply a light emitting diode (LED) adjacent to a photo sensitive transistor. DC output: Solid state relay circuit AC output: Solid state relay circuit When the LED is energised it produces light that falls on the transistor and causes it to switch on. Depending on the output configuration the transistor drives a triac to switch AC or a MOSFET to switch DC. No moving parts are required so there is nothing to wear out. Solid state relays are also sometimes referred to as “optoisolators”, “opto-couplers” or “Solenoid Drivers”. Solid state relays are very reliable and should last the life of the installation. Versions are available specifically as input devices with switching capacities of up to 100mA, or as output devices switching up to 40A inductive loads. Power solid state relay Other features of relays Relays not only provide a remote switching function but have several other important operational features. Relays can be used to interface different voltage levels or to enable large currents to be switched from low level signals. One point that is often overlooked is the electrical isolation intrinsic to the design of both electromechanical and solid state relays. Isolation is the ability to prevent the flow of current from the input to the output (or vice versa). For example a relay may be used to switch a 240V AC load but the input or coil voltage may only be 24V DC. We need to ensure the potentially dangerous voltage on the output can never arc over or allow current to flow to the input. This “isolation” is usually expressed in kilovolts. 3 How to choose the right relay for your application Many engineers and technicians can be left perplexed by the variety and diversity of relays available today. The selection criteria can differ from application to application but some common guidelines to assist in this decision can be addressed. Electromechanical may be appropriate Solid state relay may be appropriate •• Switching at less than 5 times per minute •• Standard industrial use ie PLC/ DCS output 0.5 to 10A resistive load •• Isolation up to 4kV required •• Switching at high speed, more than 5 times per minute up to 100kHz •• Industrial use as PLC/DCS input 5mA to 100mA switching •• Industrial use as an output device for inductive load switching up to 40A •• Critical switching where long life and reliable operation are paramount. Weidmüller has been manufacturing electromechanical and solid state relay products for over thirty years. Our vast installed base across all industries attests to our dedication to ensuring the most appropriate “fit for purpose” relay solutions are available to meet the demands of industry. 4 WAUS Electromechanical and Solid state relays application brochure 2013 Common issues when using relays Electrically noisy industrial environments Low Hysteresis Narrow Hysteresis band of only 3.7V. Ensures maximum rejection of industrial noise and interference Volts 24V ON 17.5V NARROW HYSTERESIS BAND 13.8V OFF MC5R-NEO MC5R – NEO is the perfect solution for all industrial switching needs. Silver contact: 7940009903 Gold contact: 7940013020 Today’s industrial plants are radiating electrical noise in every direction. Control systems are designed to reject this interference. Unfortunately miniature relays with their low input power consumption can be affected to the point that they will not switch off! One new solution to this problem is the Weidmüller’s MC5R – NEO noise rejecting relay. Another problem is the LED indication found on most relays may indicate the relay is energised. When this situation occurs it can be very difficult to find a solution. It is not uncommon to see external resistors hanging from the relay coil terminals to try and increase the input power and hence lessen its susceptibility to noise. This can work to a point but is not good engineering practice. Standard relays can fail to switch off with a coil voltage of only 4V but the MC5R NEO will reliably switch even when extreme electrical interference and noise are present. The MC5R – NEO rejects noise and switches reliably in the most arduous of conditions. With low hysteresis the 24VDC relay is unaffected by up to 13V of noise. •• High Noise Immunity •• Rejects Interference •• Change Over Contact •• 6A / 240VAC/ 24VDC 5 Electro-mechanical and solid-state relays – Comparison Relay modules and solid-state relays – Comparison Electromechanical relay Solid-state relays Fixed contacts Movable contact Receiver (Transistor) Housing Armature Coil Reset spring Coil Advantages of electromechanical relay modules (EMR) + AC and DC operation in load circuit possible Versatile (advantage as interface between different plant equipment) + No leakage current in the load circuit A semi-conductor does not achieve 100 % isolation + Low residual voltage in the load circuit Low voltage drop + No power loss in the load circuit In contrast to the semi-conductor in opto modules there is no electrical resistance in the contacts of the electromechanical relay modules that can lead to a rise in ­temperature when under load. Therefore, heat sinks are not necessary. + Multiple contacts possible A single control signal can switch several load circuits. + Control circuit less sensitive to transients Unwanted switching operations caused by voltage fluctuations are prevented by the make capacity of the magnetic coil. Transmitter (LED) Depending on the requirements, the choice between electromechanical and solid-state relays is made based on the different advantages that the different versions offer: Advantages of solid-state relays (SSR) + Long operational lifetime and reliability No moving parts or contact wear + Small dimensions Saves space on the PCB and mounting rail + Low control power An LED is activated - no mechanical parts are moved + Fast response times Fast switching, which allows high frequencies to be achieved + No contact bounce Reduces switching delays + No switching noise Suitable for use in noise-sensitive environments + Not susceptible to shock and vibration Prevents unwanted switching statuses +No electromagnetic radiation due to switching sparks or coils No interference of adjacent assemblies or electronics components 6 WAUS Electromechanical and Solid state relays application brochure 2013 Selection table Selection table TERMSERIES - Electromechanical relay modules Description TRS 24V DC 1C/O TRS 24V UC 1 C/O TRS 230V AC RC 1 C/O TRS 24V-230V UC 1 C/O TRS 24V DC 2 C/O TRS 24V UC 2 C/O TRS 230V AC RC 2 C/O TRS 24V-230V UC 2 C/O Input (coil) voltage 24V DC +/- 20% 24V AC/DC +/- 10% 230V AC +/- 10% 24-230V AC/DC +/- 10% 24V DC +/- 20% 24V AC/DC +/- 10% 230V AC +/- 10% 24-230V AC/DC +/- 10% TERMSERIES - Solid state relay modules Output (contact type) 1 CO AgNi 1 CO AgNi 1 CO AgNi 1 CO AgNi 2 CO AgNi 2 CO AgNi 2 CO AgNi 2 CO AgNi Max Switching 6A 30V DC / 250V AC 6A 30V DC / 250V AC 6A 30V DC / 250V AC 6A 30V DC / 250V AC 8A 30V DC / 250V AC 8A 30V DC / 250V AC 8A 30V DC / 250V AC 8A 30V DC / 250V AC Switching Frequency 0.1Hz (6 ops/min) 0.1Hz (6 ops/min) 0.1Hz (6 ops/min) 0.1Hz (6 ops/min) 0.1Hz (6 ops/min) 0.1Hz (6 ops/min) 0.1Hz (6 ops/min) 0.1Hz (6 ops/min) Order No. 1122770000 1122780000 1122840000 1122850000 1123490000 1123500000 1123570000 1123580000 Switching Frequency 300Hz (18,000 ops/min) 100Hz (6,000 ops/min) DC input 3Hz (180 ops/min) AC input 3Hz (180 ops/min) AC input 3Hz (180 ops/min) AC or DC input 300Hz (18,000 ops/min) 10Hz (600 ops/min) DC input 3Hz (180 ops/min) AC input 3Hz (180 ops/min) AC input 3Hz (180 ops/min) AC or DC input 3Hz (180 ops/min) 3Hz (180 ops/min) 3Hz (180 ops/min) 3Hz (180 ops/min) 300Hz (18,000 ops/min) 3Hz (180 ops/min) Order No. 1126940000 Description TOS 24V DC 48V DC 0.1A Input voltage 24V DC +/- 20% Output (contact type) Open collector bipolar transistor Max Switching 100mA 3 - 48V DC TOS 24V UC 48V DC 0.1A 24V AC/DC +/- 10% Open collector bipolar transistor 100mA 3 - 48V DC 230V AC +/- 10% 24 - 230V AC/DC +/- 10% 24V DC +/- 20% Open collector bipolar transistor Open collector bipolar transistor Power MOS-FET 100mA 3 - 48V DC 100mA 3 - 48V DC 2A 3-33V DC 24V AC/DC +/- 10% Power MOS-FET 2A 3-33V DC 230V AC +/- 10% 24 - 230V AC/DC +/- 10% 24V DC +/- 20% 24V AC/DC +/- 10% 230V AC +/- 10% 24 - 230V AC/DC +/- 10% 24V DC +/- 20% 24 - 230V AC/DC +/- 10% Power MOS-FET Power MOS-FET Triac Triac Triac Triac Open collector bipolar transistor Open collector bipolar transistor TOS 230V AC RC 48V DC 0.1A TOS 24-230V UC 48V DC 0.1A TOS 24V DC 48V DC 2A TOS 24V UC 48V DC 2A TOS 230V AC RC 48V DC 2A TOS 24-230V UC 48V DC 2A TOS 24V DC 230V AC 1A TOS 24V DC 230V UC 1A TOS 230V AC RC 230V AC 1A TOS 24-230V UC 230V AC 1A TOS 24V DC 24V DC 3.5A TOS 24-230V UC 24V DC 3.5A 1A 1A 1A 1A 2A 3-33V DC 2A 3-33V DC 24-250V AC (min 20mA) 24-250V AC (min 20mA) 24-250V AC (min 20mA) 24-250V AC (min 20mA) 3.5A 3 - 33V DC 3.5A 3 - 33V DC 1126950000 1127010000 1127020000 1127170000 1127180000 1127240000 1127250000 1127410000 1127420000 1127490000 1127500000 1127630000 1127640000 *For Solid state relays with switching outputs up to 10A 24V DC or 20A 230V AC please see catalogue below: 4.2 Relay modules and solid-state relays Catalogue 2013/2014 Let’s connect. Digital signal processing For complete overview of our Relay modules and solid-state relays catalogue. order number. 1427050000 www.weidmuller.com.au 7 Weidmüller – Partner in Industrial Connectivity. As experienced experts we support our customers and partners around the world with products, solutions and services in the industrial environment of power, signal and data. We are at home in their industries and markets and know the technological challenges of tomorrow. We are therefore continuously developing innovative, sustainable and useful solutions for their individual needs. Together we set standards in Industrial Connectivity. For all Weidmüller Product Distibutors please visit www.weidmuller.com.au/au/distributors Or contact your preferred supplier below: Weidmüller Pty Ltd (Head Office) 43 Huntingwood Drive, Huntingwood NSW 2148 Phone +61 (0) 2 9671 9999 Fax +61 (0) 2 9671 9900 Email info@weidmuller.com.au www.weidmuller.com.au Order Number: WAUS Electromechanical and Solid state relays application brochure 2013