Communication on contact-based safety relays is very limited. Simply displaying fault conditions can sometimes prove difficult. Switching to electronic versions already makes communication somewhat easier: LEDs flash, sometimes with varying frequencies, to distinguish between specific malfunctions. LCD displays indicate errors and/or operating states in plain text. Configurable safety relays offer a whole new set of options: Fieldbus modules can be used to connect them to almost any fieldbus; they can even exchange safety-related data via special interconnection modules. This enables data to be exchanged with non-safety-related fieldbus subscribers, in order to share diagnostic data or transfer control commands to the configurable safety relay, for example.
The ability to transfer data safely via special interconnection modules opens up new horizons: If several machines are working together in a network, for example, safety requirements will demand that safety signals are exchanged between the control systems. Previously this could only be achieved by exchanging digital signals. This is a laborious process and is extremely inefficient due to the high cost for each piece of information transmitted. If interconnection modules are used to replace the previous hard-wired solution; the
amount of wiring is reduced, while the amount of information data, including safety technology data, is increased.
Showing posts with label Safety relays. Show all posts
Showing posts with label Safety relays. Show all posts
Friday, August 5, 2011
Monday, August 1, 2011
Configurable Safety Relays Increase Flexibility
Similar to progress in the automation technology sector, safety technology has gradually developed from hard-wired relay technology to contact-based safety relays and devices with integrated logic function and beyond to flexible, configurable safety relays. The idea was to make safety technology more transparent and manageable for the user. This was the major driving force behind development of the devices and ultimately led also to the development of new types of configuration tools, which graphically display function and logic and then forward the configured setting to the relay via memory chip. The result is a high degree of flexibility for the responsible electrical design engineer; their plans only have to consider the number of digital and analogue inputs/outputs required. They can incorporate the functions at some later date and adapt them to suit the changed situation if necessary. At the same time, any work involved in wiring the logic functions also disappears.
With this generation of devices, the safety functions and their logic connections are configured exclusively via the software tool. The manufacturer provides the safety functions within application blocks; certified bodies such as BG or TÜV will have already tested them for safety. With the help of safe application blocks and the logic connections between these blocks, the plant or machine builder creates the safety-related application they require, an application which they would previously have implemented by wiring contactors and relays in a laborious, time-consuming process. Contacts and wires are replaced by lines between the ready-made
application blocks. An electrical circuit diagram showing the logic functions is no longer required.
Not only is it easy to connect the application blocks to each other, a simple click of the mouse is all it takes to adapt them fully to the requirements of the relevant application. Block properties define the behavior of the individual blocks within the application: whether single or multi-channel, with or without automatic reset, e.g. when a safety gate is closed. Parameters that determine how a block will behave can be easily set in accordance with the application's safety requirement.
The parameters available in the “Configure Function Element” window (see illustration) essentially mirror the familiar functions from the safety relays. They no longer have to be set laboriously on the device or be selected via jumpers; with the parameter tool everything operates in the simplest way possible. Users will find all the useful, proven elements from the world of the classic safety relays, just represented in a different format. This new configuration method has another quite simple, safety-related benefit: Once the configuration has been selected, it cannot easily be modified by unauthorized persons via screwdriver or device selector switch.
Simple configuration of the required input and output modules, plus the availability of special modules for speed or analog processing, enable the user to create a safety system that suits his own individual needs. Functions can be added or adapted later with relative ease. The user simply selects these modules from a hardware list and then creates the necessary logic functions.
With this generation of devices, the safety functions and their logic connections are configured exclusively via the software tool. The manufacturer provides the safety functions within application blocks; certified bodies such as BG or TÜV will have already tested them for safety. With the help of safe application blocks and the logic connections between these blocks, the plant or machine builder creates the safety-related application they require, an application which they would previously have implemented by wiring contactors and relays in a laborious, time-consuming process. Contacts and wires are replaced by lines between the ready-made
application blocks. An electrical circuit diagram showing the logic functions is no longer required.
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| Logic connections between the blocks for simple configuration. |
Not only is it easy to connect the application blocks to each other, a simple click of the mouse is all it takes to adapt them fully to the requirements of the relevant application. Block properties define the behavior of the individual blocks within the application: whether single or multi-channel, with or without automatic reset, e.g. when a safety gate is closed. Parameters that determine how a block will behave can be easily set in accordance with the application's safety requirement.
 |
| Configure function elements. |
The parameters available in the “Configure Function Element” window (see illustration) essentially mirror the familiar functions from the safety relays. They no longer have to be set laboriously on the device or be selected via jumpers; with the parameter tool everything operates in the simplest way possible. Users will find all the useful, proven elements from the world of the classic safety relays, just represented in a different format. This new configuration method has another quite simple, safety-related benefit: Once the configuration has been selected, it cannot easily be modified by unauthorized persons via screwdriver or device selector switch.
Simple configuration of the required input and output modules, plus the availability of special modules for speed or analog processing, enable the user to create a safety system that suits his own individual needs. Functions can be added or adapted later with relative ease. The user simply selects these modules from a hardware list and then creates the necessary logic functions.
Monday, July 25, 2011
Wiring: Contact vs. Electronic Safety Relays
For many years, wiring of the individual functions on safety relays was a complex, problematic procedure which had a negative impact on the installation process. Imagine the following situation on a machine: A safety gate is intended to prevent random, thoughtless access to a danger zone. Access is only possible once the hazardous movement has been stopped and the machine is in a safe condition, at least within the danger zone. However, the intention is for various drives to be operable at reduced speed, even when the gate is open, for installation and maintenance purposes for example. An enable switch has therefore been installed, which must be operated simultaneously.
If these requirements are to be implemented in practice, so that the operator is protected from potential hazards, a substantial amount of wiring will be needed to connect the individual safety devices. As well as the actual protection for the safety gate, safety relays will also be required for the enable switch, to monitor “Setup” mode, and for the master emergency off/emergency stop function. Reduced purely to the logic relationships, the connections could look as follows:
If this application is implemented using classic contact-based devices, the design will correspond approximately to the diagram below:
The diagram shows that implementation via contact-based devices produces a result which is not entirely comprehensible; it is also very cost intensive due to the vast amount of wiring involved. In recognition of this fact, consideration almost inevitably turned to a simpler form of implementation, using logic connections between the safety relays. Thus started the development of a new type of device with integrated connection logic.
Microprocessor technology opened up a whole new range of possibilities, as expressed by the predominantly electronic devices in the PNOZelog product series, for example. It laid the foundations for previously unimagined flexibility: One device can now be set for different application areas, another device for different safety functions. Unlike conventional safety relays, these new relays have electronic safety outputs and auxiliary outputs that use semiconductor technology. As a result they are low-maintenance and non-wearing and are therefore suitable for applications with frequent operations or cyclical functions. In addition to the actual basic function, such as monitoring a safety gate or an emergency off/emergency stop function for example, these devices contain a logic block with special inputs, enabling logic AND / OR connections between the devices. An output block with auxiliary outputs and safety outputs completes the safety relay.
The following application example shows how the above example is implemented using electronic safety relays from the stated product series. Compared with a design using contact-based technology, the diagram is much clearer and the amount of wiring is drastically reduced.
If these requirements are to be implemented in practice, so that the operator is protected from potential hazards, a substantial amount of wiring will be needed to connect the individual safety devices. As well as the actual protection for the safety gate, safety relays will also be required for the enable switch, to monitor “Setup” mode, and for the master emergency off/emergency stop function. Reduced purely to the logic relationships, the connections could look as follows:
If this application is implemented using classic contact-based devices, the design will correspond approximately to the diagram below:
The diagram shows that implementation via contact-based devices produces a result which is not entirely comprehensible; it is also very cost intensive due to the vast amount of wiring involved. In recognition of this fact, consideration almost inevitably turned to a simpler form of implementation, using logic connections between the safety relays. Thus started the development of a new type of device with integrated connection logic.
Microprocessor technology opened up a whole new range of possibilities, as expressed by the predominantly electronic devices in the PNOZelog product series, for example. It laid the foundations for previously unimagined flexibility: One device can now be set for different application areas, another device for different safety functions. Unlike conventional safety relays, these new relays have electronic safety outputs and auxiliary outputs that use semiconductor technology. As a result they are low-maintenance and non-wearing and are therefore suitable for applications with frequent operations or cyclical functions. In addition to the actual basic function, such as monitoring a safety gate or an emergency off/emergency stop function for example, these devices contain a logic block with special inputs, enabling logic AND / OR connections between the devices. An output block with auxiliary outputs and safety outputs completes the safety relay.
The following application example shows how the above example is implemented using electronic safety relays from the stated product series. Compared with a design using contact-based technology, the diagram is much clearer and the amount of wiring is drastically reduced.
Thursday, July 14, 2011
Structure and Function of Safety Relays
Today's safety relays are distinguished primarily by their technological design:
Nothing has changed in the fundamental requirement that safety relays must always be designed in such a way that – when wired correctly – neither a fault on the device nor an external fault caused by a sensor or actuator may lead to the loss of the safety function. Technological change has advanced the development of electronic safety relays, which offer much greater customer benefits: Electronic devices are non-wearing, have diagnostic capabilities and are easy to incorporate into common bus systems for control and diagnostic purposes.
The typical design of a first generation safety relay in relay technology is based on the classic 3 contactor combination. The redundant design ensures that wiring errors do not lead to the loss of the safety function. Two relays (K1, K2) with positive-guided contacts provide the safe switch contacts. The two input circuits CH1 and CH2 each activate one of the two internal relays. The circuit is started via the start relay K3. There is another monitoring circuit between the connection points Y1 and Y2 (feedback loop). This connection is used to check and monitor the position of actuators which can be activated or shut down via the safety contacts. The device is designed in such a way that any faults in the input circuit are detected, e.g. contact welding on an emergency off/emergency stop pushbutton or on one of the safety contacts on the output relay. The safety device stops the device switching back on and thereby stops the activation of relays K1 and K2.
- Classic contact-based relay technology
- With electronic evaluation and contact-based volt-free outputs
- Fully electronic devices with semiconductor outputs
Nothing has changed in the fundamental requirement that safety relays must always be designed in such a way that – when wired correctly – neither a fault on the device nor an external fault caused by a sensor or actuator may lead to the loss of the safety function. Technological change has advanced the development of electronic safety relays, which offer much greater customer benefits: Electronic devices are non-wearing, have diagnostic capabilities and are easy to incorporate into common bus systems for control and diagnostic purposes.
 |
| Structure and Function of Safety Relays |
The typical design of a first generation safety relay in relay technology is based on the classic 3 contactor combination. The redundant design ensures that wiring errors do not lead to the loss of the safety function. Two relays (K1, K2) with positive-guided contacts provide the safe switch contacts. The two input circuits CH1 and CH2 each activate one of the two internal relays. The circuit is started via the start relay K3. There is another monitoring circuit between the connection points Y1 and Y2 (feedback loop). This connection is used to check and monitor the position of actuators which can be activated or shut down via the safety contacts. The device is designed in such a way that any faults in the input circuit are detected, e.g. contact welding on an emergency off/emergency stop pushbutton or on one of the safety contacts on the output relay. The safety device stops the device switching back on and thereby stops the activation of relays K1 and K2.
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