With generation I and II SERCOS interfaces, one fiber optic ring is used to communicate 32-bit data between controllers, drives, I/O and sensors. This includes commands, status, parameters and diagnostics. In SERCOS-III, standard Industrial Ethernet is normally used for this purpose. Note that Ethernet fiber optics can be used for communication in SERCOS-III.
Fiber optics provide noise immunity and eliminate the immense requirements for conduit, wiring and terminations normally required with an analog interface. The ring architecture reduces the number of components required on a motion control. Adding an additional motion axis often requires nothing more than opening the ring and placing the new drive in the ring.
A SERCOS interface ring is composed of a number of fiber optic segments having no braches – master-to-slave, slave-to-slave and last-slave-back-to-master as illustrated in
topology. Each device in a system receives signals via a fiber optic receiver with an F-SMA connector (Fiber Optic Subminiature Version A), and transmits the signals to the next device via a fiber optic transmitter, again with a standard F-SMA connector.
Fiber Optic Cable
The fiber optic cable consists of 1 mm Plastic Optical Fiber (POF) or 200 µm Hard Clad Silica (HCS) (glass) multi-mode optical fiber with a step index profile or graded index profile. Fiber optic cables and cores can be used. Only fiber optic cables with a wavelength of 650 nm are specified for SERCOS. For fiber optic materials currently in use, the attenuation is approximately 220 dB/km for plastic and 6 dB/km for glass.
The following drawing illustrates the structure of a typical fiber optic cable. Note that the SERCOS interface standard does not specify the outer diameter of the cables. Typically, 2.2 mm diameter cables are used inside equipment cabinets. These cables do not have the strength members shown in the drawing. Typically, 3.6, 5 and 6 mm diameter cables are used for cabinet-to-cabinet connections.
Structure of a single-core fiber optic cable
Cable Specifications
|
Plastic
Fiber - POF |
Glass Fiber - HCS |
| Core
diameter |
980 µm |
200 µm |
| Cladding
diameter |
1000 µm |
230 µm |
| Numeric
aperture |
0.47 |
0.37 |
| Bandwidth |
>= 5 MHz * 1 km |
>= 10 MHz * 1 km |
 |
|
|
|
Fiber Optic Connectors
SERCOS fiber optic cable connectors are specified as:
-- Shall correspond to F-SMA standard (see IEC 60874-2).
-- Shall have a quality level of at least 5.
-- Shall have a metallic connector ring.
In addition, it is recommended that fiber optic cables have a strain relief.
Sources For Fiber Optic Cables
Assembled and tested SERCOS fiber optic cables are available from all SERCOS members who supply controls and drives.
See our member lists
and contact the sales department of the appropriate company or check their website for your local distributor.
SERCOS N.A. member Industrial Fiber Optics is a specialist in fiber optics, supplying fiber optic components, test equipment, connectors, optical cable and completely assembled and tested SERCOS plastic and glass fiber optic cables in various cable types and lengths.
See the SERCOS page on the Industrial Fiber Optics
website. Contact Randy
Dahl, president, with any questions about optical fiber problems or solutions.
480/804-1227.
Fiber Optic Ring Lengths
A SERCOS interface ring is composed of a number of fiber-optic segments. Maximum cable lengths are:
| Cable Type |
Maximum Cable Length |
| Plastic fiber – POF (1 mm diameter) |
|
| Node-to-node |
40
meters |
Maximum ring length (254 nodes per ring)
|
10,000+ meters |
| Glass
fiber – HCS (200 µm diameter) |
|
| Node-to-node |
200
meters |
| Maximum ring length (254 nodes per ring) |
50,000+ meters |
|
|
|
If a coupling is used to pass a cable through a cabinet wall, the maximum length of that segment is reduced by 6 meters.
The maximum number of drops per fiber-optic ring is 254. However, the number of drives that can be serviced per ring depends on three application requirements:
-- The communication cycle time.
-- The volume of operational data.
-- The communications speed required.
The number of rings that can be synchronized together is limited only by the controller, which will have a limit to the number of axes it can process. SERCOS interface-compliant controllers can have a much higher axis limit than their predecessors, since the SERCOS interface supports distributed processing, which relieves the controller of many time-intensive tasks, which are now handled by the drives.
Performance of SERCOS interface Rings -- Generation I and II
Cycle
Time |
Data
Record
Per Drive
(MDT + AT) |
Transmission
Rate |
Number
of
Drives |
Data
Rate
(Non-cyclic
Data) |
Remaining
Cycle
Time |
| 2
ms |
32
Bytes |
2 Mbit/sec |
8 |
8 kbit/s
(2 bytes) |
390µs |
| 1
ms |
32
Bytes |
4
Mbit/sec |
8 |
16
kbit/s
(2 bytes) |
125µs |
| 1
ms |
36
Bytes |
8
Mbit/sec |
15 |
32
kbit/s
(4 bytes) |
208µs |
| 0.5
ms |
36
Bytes |
16
Mbit/sec |
14 |
128
kbit/s
(8 bytes) |
113µs |
| 2
ms |
Standard
Telegram
2,3,4 |
16
Mbit/sec |
112 |
8
kbit/s
(2 bytes) |
330µs |
|
|
|
|
|
|
|
Fiber Optic Transmitters/Receivers
Fiber optic transmitters and receivers from Avago Technologies and Honeywell have been tested and approved by the SERCOS Technical Working Group. The
Download section of this website provides links to downloadable data sheets for these products. Signal levels are defined in the IEC61491 standard.
Avago Technologies (formerly Agilent Technologies):
Avago HFBR1505A / 2505A -- optical components are specified up to 10 Mbit/s only
Avago HFBR 1506AM/2506AM -- available with metallized plastic
thread. Specified for operation up to 16 Mbit/s.
Products can be purchased from Avago's
distributors.
Europe: For additional information, please contact Mr.
Schwaiger.
Tel +49(0)7031 436 3201, Fax 49(0)7031 436 3369.
Honeywell:
Honeywell offers a new transmitter (HFE7000) which is applicable for 16 Mbit/s. Receivers HFD 7000 and HFD 7500 comply with the specification. HFD 7500 is cheaper than the HFD 7000, but it needs a comparator, since the output signal is not interoperable with TTL.
Honeywell offers its optical units with either plastic or metal thread.
In North America, these products are distributed by Arrow. For additional information, please contact
Mr. Joch.
Tel +49-(0)89-35 81 33 17
Fiber optic receivers and transmitters are available from other manufacturers as well, but thus far, they have not been tested for compliance with the SERCOS specifications.
Fiber Optic Repeaters
Periodically, we receive inquiries regarding fiber optic repeaters for SERCOS; however, there are no repeaters specified. For longer lengths, use glass fiber up to 400 meters in length. If that isn't adequate, increase the optical output power of the transmitter.
Rotary Fiber Optic Joints
Rotary fiber optic joints for use in SERCOS systems are manufactured in North America by SERCOS N.A. member Princetel, Inc.
Contact Barry Zhang, President
Princetel, Inc.
1595 Reed Road, Suite 300
Pennington, NJ 08534
Tel:609-895-9890
Fax: 609-895-9552
barryzhang@princetel.com
www.princetel.com
Rotary fiber optic joints are manufactured in Europe by Schleifring.
Schleifring und Apparatebau GmbH
Am Hardtanger 10
D-82256 Fuerstenfeldbruck. Germany
Schleifring North America, LLC
226 Lowell Street
Wilmington, MA 01887
Tel: 978-988-8780
Fax: 978-988-8783
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