Benefits derived from the FF specification FF-831

Size: px

Start display at page:

Download "Benefits derived from the FF specification FF-831"

Mervyn Shelton
5 years ago
Views:

1 Foundation Fieldbus End Users Council Australia Inc. 9 Corcoran St Duncraig, WA 6023 P.O. Box Z5546 Perth, WA 6831 Benefits derived from the FF specification FF-831 Why we need it, and why it improves interoperability and stability Andreas Agostin Pepperl+Fuchs Pte Ltd Singapore In March 2004, the Fieldbus Foundation released the Fieldbus Power Supply Test Specification FF-831. This specification describes tests and measurement procedures for Foundation Fieldbus power supplies and conditioners. FF-831 is based on the existing physical layer specifications IEC : 2003, FF and FF , but considers tests beyond the requirements of these standards that determine if the power supply is fit for its intended purpose of powering a fieldbus network. Therefore some implementations will meet the requirement of the standard IEC but will not pass the conformance test FF-831. The paper will describe the performed tests and in what aspects FF-831 exceeds the requirements of the IEC standard. It will explain why extended requirements are necessary and will show what techniques are required for the next generation of FF power supplies. One of the already registered Fieldbus Power Supplies of the next generation, the Fieldbus Power Hub, will serve as an example to investigate the required technology. The paper will conclude with the positive impact FF-831 has on Fieldbus stability in general and user installations in particular. Keywords: Fieldbus Power Supply, Fieldbus Power Conditioner, Physical layer, FF-831 specification, IEC standard Page 1 of 15

2 Table of content 1. Introduction Differences in the supplies Standardisation compliance FF-831:2004 Tests Applicability Test No. 1: Output voltage Test No. 2: Noise and Ripple Test No. 3: Timing Test No. 4: Resonance Test No. 5 and 6: Startup Test No. 7: Short circuit Test No. 8: Add device Test No. 9: Galvanic isolation Test No. 10: Multi Segment test short circuit Test No. 11: Multi Segment test Signal isolation (crosstalk) Conclusion List of abbreviations References...15 Andreas Agostin, Pepperl+Fuchs Pte Ltd Singapore Page 2 of 15

3 1. Introduction During the last three years of presentations at the Jump Aboard meeting in Australia, Pepperl+Fuchs highlighted the technical advances of the network interconnection topologies, leading to more and more supply power even for hazardous (potentially explosive) areas. Additionally, Fieldbus concepts like FISCO, FNICO, the Fieldbus barrier and others further diversify the topology solutions. This led to a larger number of supplies and conditioners available on the market today, and the customer now has the choice to select the most appropriate one for his application. But what are the differences? Is it just the amount of output voltage and current, or is there more than that? And if the supplies all comply with the physical layer specification (IEC ), why do the supplies perform differently? The new Foundation Fieldbus specification FF-831 (Version 1.0) goes beyond the IEC specification, and considers network behaviour rather than component (isolated) behaviour. Andreas Agostin, Pepperl+Fuchs Pte Ltd Singapore Page 3 of 15

4 2. Differences in the supplies With Foundation Fieldbus, data communication (information) and power are on the same cable; the communication is superimposed on the power (figure 1). Communication is fully digital. The field instruments do consume current, but this current is constant (typically somewhere around 20mA) and does not represent any process information like with a 4-20mA instrument. The constant current is required to operate the device; all signal values (measurement value like flow, temperature, pressure, etc) are communicated digitally (similar to the HART communication). U Bus Normal bus voltage t Superimposed communication Figure 1: Communication superimposed to the power To allow communication to be on top of the supply power, the communication must be decoupled from the voltage regulation units (Power Supply), as a voltage regulation unit tries to maintain a fixed output voltage at its output terminals, hence this would eliminate any signal that tries to be imposed on the network power. This decoupling is done via a low pass filter : the DC voltage can pass, but the higher frequency communication signal cannot pass the filter and is decoupled from the voltage regulator (DC/DC converter) (see figure 2). Andreas Agostin, Pepperl+Fuchs Pte Ltd Singapore Page 4 of 15

5 To host communication controller FF Power Supply Standard (bulk) Power Supply, e.g. 24V + - DC/DC converter + - Low Pass Filter (f < 3kHz pass) To field Figure 2: Isolated Fieldbus Power Supply For non-isolated Fieldbus Power Conditioners (figure 3), the additional power conversion unit to provide symmetry is eliminated, but the filter itself must be symmetrical to achieve the required impedance characteristics. To host communication controller FF Power Conditioner Standard (bulk) Power Supply, e.g. 24V + - Low Pass Filter (f < 3kHz pass) To field Figure 3: Fieldbus Power Conditioner Andreas Agostin, Pepperl+Fuchs Pte Ltd Singapore Page 5 of 15

6 This becomes more obvious looking at the schematic drawing (principle) (figure 4). FF Power Supply Z FF Power Conditioner Z/2 Non-symmetrical filter Symmetrical filter Z/2 Figure 4: Schematic drawing of Power Supply and Power Conditioner Additionally, there are different methods of how to build a low-pass filter. Today, there are two methods used: an active filter and a passive filter. An active filter uses an electronic circuit called Gyrator to build the required impedance; passive filters use either inductors and/or resistors to build the required impedance. Active filters are usually smaller in size, but can only be built non-symmetrically due to the electronic control circuitry 1, which again requires additional galvanic isolation. Passive filters are symmetrical (at least if the conditioner is according to the FF-831), so that no galvanic isolation is required to provide any symmetry. To summarize the differences: A FF Power Supply always has galvanic isolation, and can be used with either active or passive filter. A FF Power Conditioner always has a passive (and symmetrical, to comply with FF-831) filter, and does not have galvanic isolation. 1 If active circuitry would be used symmetrically, two parallel control units would compete against each other, which would result in unstable operation. Andreas Agostin, Pepperl+Fuchs Pte Ltd Singapore Page 6 of 15

7 3. Standardisation compliance All Foundation Fieldbus equipment, whether it is a host, instrument, supply or conditioner, has to comply with the IEC standard. The current 3 rd edition was published in 2003 and previous releases are no longer valid. The IEC :2003 defines the physical layer of different field buses. Its official name is: Digital data communications for measurement and control Fieldbus for use in industrial control systems Part 2: physical layer specification and service definition. This standard covers wire media and optical transmission, and different transmission speeds. The Fieldbus Foundation released a number of specifications that are to be applied for FF products. Among these is the FF-816 Ver. 1.5, defining that FF-H1 (Foundation Fieldbus, 31.25kBit/s) uses the medium attachment units for a wire medium with 31.25kBit/s transmission speed and voltage signalling. It classifies a number of types that identify whether a supply is IS or non-is, FISCO, instrument, supply, etc. The FF-830 Ver. 1.5 defines test procedures to ensure that the device conforms to the IEC The FF-831:2004 was released in March 2004 and defines a number of tests to ensure proper network behaviour of supplies and conditioners. Andreas Agostin, Pepperl+Fuchs Pte Ltd Singapore Page 7 of 15

8 4. FF-831:2004 Tests 4.1. Applicability The FF-831 specification is applicable for both isolated Fieldbus Power Supplies and for non-isolated Fieldbus Power Conditioners. The following types are defined: Galvanically isolated power supply with integrated conditioners: Fieldbus Power Supply Two types of non-isolated conditioners (I.e. no integrated additional power supply). Type 1: used with non-specific general purpose bulk power supplies Type 2: used with specific (i.e. limited choice) general purpose bulk power supplies. The compliance test is to be performed by the manufacturer, and the test report FF- 832 must be submitted to the Foundation Fieldbus organization. If the supply or conditioning systems use redundant parts/modules, the redundant parts/modules have to be taken out of the system before the tests are performed (see figure 5). This guarantees proper operation with single (non-redundant) modules. Figure 5: Remove redundant components while performing the tests Andreas Agostin, Pepperl+Fuchs Pte Ltd Singapore Page 8 of 15

One example of the new generation of FF-831 compliant devices is the Pepperl+Fuchs Fieldbus Power Hub. The unit has two entries on the Fieldbus.org website.

9 One example of the new generation of FF-831 compliant devices is the Pepperl+Fuchs Fieldbus Power Hub. The unit has two entries on the Fieldbus.org website. The following table shows how the entries are listed: Manufacturer - Pepperl + Fuchs Product Name - Fieldbus Power Hub Model Number - HD2-FBCL (Module) with MB-FB-*.* (Backplane) Revision (HD2-FBCL-1.500); 1.0 (MB-FB- *.*) Type - Power Conditioner Type 1 H1 Profile Campaign - PS Registration Date - April 30, 2004 The modules: Manufacturer - Pepperl + Fuchs Product Name - Fieldbus Power Hub Model Number - HD2-FBPS (Module) with MB-FB-*.* (Backplane) Revision (HD2-FBPS-1.500); 1.0 (MB-FB- *.*) Type - Power Supply H1 Profile Campaign - PS Registration Date - April 30, 2004 Backplane with modules Power Supply and Conditioner look the same Figure 6: Modules and backplane of the Fieldbus Power Hub The registration information in the table above shows two types of modules: A Power Conditioner Type 1 (for the module HD2-FBCL-1.500) and a Power Supply (for the module HD2-FBPS-1.500). The board (MB-FB-*.*) is used universally and connects to redundant bulk supplies. What is so special about the Fieldbus Power Hub? With the same design and the same backplane, the user can select between (redundant) Conditioner and (redundant) Power Supply. The choice will be based on features and price. Andreas Agostin, Pepperl+Fuchs Pte Ltd Singapore Page 9 of 15

10 4.2. Test No. 1: Output voltage The supply/conditioner has to maintain the output voltage that is specified in the datasheet, with a 20mA (simulates one device), 50% and 100% load Test No. 2: Noise and Ripple The IEC specifies noise levels only for transmitting devices. As a supply/conditioner is not transmitting, the respective specification does not apply. Hence, FF-831 creates a specification for these components Test No. 3: Timing Like noise, timing also applies to transmitting devices only. The test in FF-831 makes sure that a supply does not have an impact on such transmitting devices. As the test environment does not contain cable, surge protectors or external noise, the requirement for the timing parameter is slightly more stringent that the IEC standard Test No. 4: Resonance This test simulates different earth faults at the supply side, which are not allowed to have an impact on the supply/conditioner. The test is to ensure that the bulk power supply used has no impact on the proper behaviour of the supply/conditioner. Andreas Agostin, Pepperl+Fuchs Pte Ltd Singapore Page 10 of 15

11 4.6. Test No. 5 and 6: Startup Switching-on the bulk supply with all instruments connected could be one likely scenario. This test simulates a load that draws up to 3 times the normal operating current during startup. A second scenario is to have the supply powered and then connect the Fieldbus cable with all instruments wired. Again, the supply/conditioner must be able to provide up to 3 times the nominal load current Test No. 7: Short circuit The supply/conditioner must be able to withstand a continuous short circuit. Short circuits can happen during commissioning, troubleshooting or maintenance. After removing the short circuit, the supply/conditioner must recover within 20ms to normal operation Test No. 8: Add device During this test, a 20mA load (representing 1 instrument) is connected in addition to the Fieldbus segment running at maximum current less than 20mA, so that after connection, the bus is running at full load. 20ms after the connection, the voltage must be at least 95% of the specified minimum output voltage of the supply/conditioner. Andreas Agostin, Pepperl+Fuchs Pte Ltd Singapore Page 11 of 15

12 4.9. Test No. 9: Galvanic isolation This test applies to galvanically isolated Fieldbus power supplies only. The isolation must withstand 500VACrms Test No. 10: Multi Segment test short circuit A short circuit on one segment must not have a significant impact on any other segment, whether isolated supplies or non-isolated conditioners are used on the same bulk power supply. The impact is insignificant if the voltage drops not more than 20% within 100us (microseconds), and is within +/-5% after 100us Test No. 11: Multi Segment test Signal isolation (crosstalk) Multiple segments could be powered by the same bulk power supply or by a set of multiple galvanically isolated Fieldbus Power Supplies. In such cases, there could be crosstalk from one segment to the other via supply. This test measures the crosstalk between segments, which must be a maximum of 14.5mVpp (approx. 1.5% of the communication signal). Andreas Agostin, Pepperl+Fuchs Pte Ltd Singapore Page 12 of 15

13 5. Conclusion Having described the tests, one can say that FF-831 performs multiple tests that are not part of any other specification, e.g. physical layer spec. IEC :2003. One of the main statements of this specification is that both galvanically isolated Fieldbus Power Supplies and non-isolated Fieldbus Power Conditioners can be used to power Fieldbus networks, and as long as they comply with the tests, both of them perform equally well. A second statement is that multiple supplies or conditioners can be powered from one and the same bulk supply. Such a powering method has no negative impact on the behaviour of the Supply/Conditioner, as long as the Supply/Conditioner passes the FF-831 tests. The tests of FF-831 ensure proper Network behaviour of both isolated supplies and non-isolated conditioners, and go beyond simple component definitions as in e.g. the IEC :2003. The tests consider proper operation of such units even in case of wiring faults, overload, startup or maintenance. To have a common platform to measure Power Supplies and Conditioners is beneficial for the end user and ensures interoperability and improves stability, because the test suite ensures that the Supply/Conditioner fulfils this purpose under all normal and even many abnormal operating conditions. Supplies/Conditioners that pass the FF-831 test suite are listed on the Fieldbus.org website, currently on Andreas Agostin, Pepperl+Fuchs Pte Ltd Singapore Page 13 of 15

14 6. List of abbreviations CAN DMM EMC Ex e Ex i FF FF-H1 FF-HSE FISCO FNICO FuRIOS HSE IS Controller Area Network. Bus system used in cars. Digital multimeter. Electromagnetic compatibility. Protection method increased safety. Predominantly defining mechanical requirements for cabling, connections, housings, etc. see IS 1. Fieldbus Foundation (organisation). 2. Foundation Fieldbus (protocol defined by the Fieldbus Foundation). Foundation Fieldbus with 31.25kBit/s transmission rate see HSE Abbreviation for Fieldbus Intrinsically Safe COncept. Method of designing a Fieldbus network based on experiences and tests of the German certification institute PTB, for Zone 1 and Zone 0 applications. Abbreviation for Fieldbus Non-incendive COncept. Method of designing a Fieldbus network based on FISCO, but for Zone 2 applications. German abbreviation for Fieldbus and Remote I/O system comparison. A study initiated by two huge German end users, Aventis Pharma and InfraServ Hoechst, comparing a existing plant using remote-i/o technology and conventional point to point technology with a designed plant using fieldbus. High Speed Ethernet. Uses standard Ethernet with 10MBit/s, 100MBit/s or 1GBit/s (future) for the data transmission. Intrinsic Safety. Protection method based on energy limitation for use in Andreas Agostin, Pepperl+Fuchs Pte Ltd Singapore Page 14 of 15

15 potentially explosive (hazardous) areas. ISO MAU P+F TCP/IP up USB OSI International Standardisation Organisation. Medium attachment unit. Electronic/mechanical/optical circuit that connects to the transmission medium (cable/fiber optics/antenna) Abbreviation for Pepperl+Fuchs. Internet transmission protocol. Micro processor. Universal Serial Bus. Bus used in personal computers (PC) for the connection of periphery (e.g. printers, scanners). Open System Interconnection. Model defining a networking framework for implementing protocols in seven layers. 7. References IEC :2003 Digital data communications for measurement and control Fieldbus for use in industrial control systems Part 2: physical layer specification and service definition FF FOUNDATION Specification. Physical Layer Profile. FF FOUNDATION Specification kBit/s Physical Layer Conformance Test. FF-831:2003 FOUNDATION Specification. Fieldbus Power Supply Test Specification. Andreas Agostin, Pepperl+Fuchs Pte Ltd Singapore Page 15 of 15

New FOUNDATION Fieldbus Interface Techniques Increased Availability and Reduced Costs. Andreas Agostin Pepperl+Fuchs

New FOUNDATION Fieldbus Interface Techniques Increased Availability and Reduced Costs Andreas Agostin Pepperl+Fuchs Abstract InfraServ Hoechst and Aventis Pharma of Germany performed a comparison study