Serial to Fiber Optic Converter Preliminary - 2-9-2009
WattMaster Controls, Inc. 8500 NW River Park Drive Parkville, MO 64152 Toll Free PH: (866) 918-1100 PH: (816) 505-1100 FAX: (816) 505-1101 E-mail: mail@wattmaster.com Visit our web site at www.wcc-controls.com Form: WM-FBROPTICS-TGD-01A Copyright 2009 WattMaster Controls, Inc. WattMaster Controls, Inc. assumes no responsibility for errors, or omissions. This document is subject to change without notice. 2 Operator Interface
Introduction Introduction to Fiber Optics In recent years it has become apparent that fiber-optics are steadily replacing copper wire as an appropriate means of communication signal transmission. They span the long distances between local phone systems as well as providing the backbone for many network systems. WattMaster Controls, Inc. has designed an RS-485 to Fiber Optic device to work with the WCC III communication network as well as with WattMaster s other product lines Orion and Auto- Zone. Figure 1: WattMaster Controls, Inc. Serial to Fiber Optic Converter for the WCC III System Operator Interface 1
Fiber Optic System Overview A fiber-optic system is similar to the copper wire system that fiber optics is replacing. The difference is that fiber optics use light pulses to transmit information down fiber lines instead of using electronic pulses to transmit information down copper lines. Looking at the components in a fiber-optic chain will give a better understanding of how the system works in conjunction with wire based systems. At one end of the system is an optical transmitter. This is the place of origin for information coming on to fiber-optic lines. The optical transmitter accepts coded electronic pulse information coming from copper wire. The RS-485 to Fiber Optic board (PL102335) then processes and translates that information into equivalently coded light pulses. An injection-laser diode (ILD) is used for generating the light pulses. Using a lens, the light pulses are funneled into the fiber-optic medium where they then travel down the cable. The light (near infrared) that is used within the PL102335 device is 850nm and is generally used for shorter distances up to 2.5 miles long. Think of a fiber cable in terms of very long cardboard roll (from the inside roll of paper towel) that is coated with a mirror on the inside of the tube. If you shine a flashlight in one end, you can see light come out at the far end - even if it s been bent around a corner. Light pulses move easily down the fiber-optic line because of a principle known as total internal reflection. This principle of total internal reflection states that when the angle of incidence exceeds a critical value, light cannot get out of the glass; instead, the light bounces back in. When this principle is applied to the construction of the fiber-optic strand, it is possible to transmit information down fiber lines in the form of light pulses. The core must be a very clear and pure material for the light or in most cases near infrared light (850nm, 1300nm, and 1500nm). The core can be plastic (used for very short distances) but most are made from glass. Glass optical fibers are almost always made from pure silica. There are three types of fiber optic cable commonly used: single mode, multimode, and plastic optical fiber (POF). The RS-485 to Fiber Optic board (PL102335) uses single mode cable. Single Mode cable is a single strand (the RS-485 to Fiber Optic module (PL102335) application requires the use of 2 fibers) of glass fiber with a diameter of 8.3 to 10 microns that has one mode of transmission (RX or TX). Single Mode Fiber with a relatively narrow diameter through which only one mode will propagate carries higher bandwidth than multimode fiber but requires a light source with a narrow spectral width. Single mode fiber gives you a higher transmission rate and up to 50 times more distance than multimode, but it also costs more. Single mode fiber has a much smaller core than multimode. The small core and single light-wave virtually eliminate any distortion that could result from overlapping light pulses, providing the least signal attenuation and the highest transmission speeds of any fiber cable type. Optical fibers are connected to terminal equipment by optical fiber connectors. These connectors are usually of a standard type such as FC, SC, ST, LC, or MTRJ. The FOSTC uses the ST connectors. 2 Operator Interface
Dip-Switch Detail The WattMaster Controls, Inc. Serial to Fiber Optic Converter for the WCC III system consists of two parts. The FOSTC Serial to Fiber Optic Converter and the FOSTC Serial to Fiber Optic adaptor board. With the cover off of the FOSTC Fiber Optic to Serial Converter, Figure 2 shows the Switch detail of the FOSTC Serial to Fiber Optic Converter (shown set for WCC III SAT III communications.) In order for the FOSTC Fiber Optic to Serial Converter to work with the WCC III communication, the internal Dip-switch as shown in Figure 2 must be properly set. Please remove the cover and verify the dipswitch setting. The WCC III SAT communications is 19.2K, RS-485 / 2-Wire Mode. WattMaster Controls modifies/replaces the standard RS-485 driver in the standard FOSTC Serial to Fiber Optic Converter. This newer driver chip that is installed can handle +/- 60 Volts of differential voltages on the RS-485 R and T connections with respect to ground. The standard RS-485 driver chips can only handle -7 to +12 Volt of differential voltages on the RS-485 R and T connections with respect to ground. Figure 2: Serial to Fiber Optic Converter Switch Detail for the WCC III System Operator Interface 3
Dip-Switch Setup Dip-Switch Setup The Dip-Switch (SW1) on the FOSTC defines the mode of operation when being used for RS-422 or RS-485. Positions 1 through 5 on the switch determine the timeout of the RS-485 driver. Because the driver is controlled by hardware, a specific time must be set to tell the hardware how long to wait for data on the fiber side before turning off the RS-422/485 driver. If this time is set too short, the driver could be disabled before transmission is complete, resulting in data corruption. If the time is set too long, the RS-485 device may respond before the RS-422/485 driver in the FOSTC is disabled, thus corrupting this response. We recommend that the timeout be set for approximately one character time or longer. The character times for several different baud rates are selectable on switch positions 1 through 5. If you need a different timeout than what is provided, R10 can be removed and replaced with a different value R9. Table 1 shows different timeout values for the switch positions as well as typical R9 replacement values. RS-485 Timeout Selection Baud Rate R9 Time(ms) Pos. 1 Pos. 2 Pos. 3 Pos. 4 Pos. 5 1200 820 K 8.20 2400 430 K 4.30 4800 Not Used 2.20 9600 Not Used 1.30 19.2K Not Used 0.56 38.4K Not Used 0.27 57.6K Not Used 0.22 76.8K Not Used 0.14 115.2K Not Used 0.10 153.6K 6.2 K 0.06 230.4K 4.3 K 0.04 460.8K 2.2 K 0.02 ON OFF OFF OFF OFF ON OFF OFF OFF OFF OFF OFF OFF OFF ON OFF OFF OFF ON OFF OFF OFF ON OFF OFF OFF ON OFF OFF OFF ON OFF OFF OFF OFF ON OFF ON ON OFF ON ON ON OFF OFF ON OFF OFF OFF OFF ON OFF OFF OFF OFF ON OFF OFF OFF OFF Position 6 of SW1 sets the unit in a Multidrop mode or a Pointto-Point mode. When the FOSTC is set in a Multidrop mode, data arriving on the Fiber Optic receiver is repeated back out the transmitter. When set in a Point-to-Point mode, data arriving at the Fiber Optic receiver is not sent back out the Fiber Optic transmitter. Position 6 must be turned On when the FOSTC is to be used in a multi-drop ring configuration and must be turned Off when the FOSTC is to be used as either end of a pointto-point communication line. See Figure 3 for typical system setups using the FOSTC in its different modes. Positions 7 and 8 of SW1 determine when the RS-422/485 driver and receiver are enabled. Position 7 controls the driver and Position 8 controls the receiver. For RS-422 operation, set both switches to the Off position. For multi-drop RS-485 fourwire systems, position 7 should be On and position 8 should be Off. This allows the receiver to be enabled all of the time and eliminates some possible timing problems. For RS-485 two-wire systems, both switches should be in the On position. This disables the RS-422/485 receiver whenever the driver is enabled, preventing data from being echoed back to the fiber side of the FOSTC. Table 2 illustrates the switch settings for typical setups. 422/485 Switch Settings RS-485 2-Wire Mode (Half Duplex) RS-485 4-Wire Mode (Full Duplex) RS-422 Mode (Full Duplex) Position 7 TX Enable ON ON OFF Table 2: 422/485 Switch Settings Position 8 RX Enable ON OFF OFF Table 1: RS-485 Timeout Selection 4 Operator Interface
Fiber Optic Adapter Board Figure 3: The PL102334 FOSTC Fiber Optic Adapter Board Fiber Optic Adapter Board The PL102334 FOSTC Fiber Optic Adapter Board provides for a two-wire, RS-485 interface to the FOSTC Fiber Optic converter for the WCC III / SAT III communications loop. It is also the power supply for the FOSTC Serial to Fiber Optic Board. RS-485 BIAS Jumpers The RS-485 BIAS jumpers for the terminating resistors need to be ON only when there is no WCC III - MCD connected to the FOSTC fiber optic adapter board s SAT RS-485 communication loop. It is recommended that this circuit board has its own 24 VAC transformer for optimal isolation on the RS-485 side. The LED D3 POWER will light when the PL102334 circuit bard has power (24VAC) applied to it. The LED D4 COMM will blink with the flow of data to and from the RS-485 communications loop. The RS-485 BIAS jumpers for the terminating resistors need to be OFF only when there is a WCC III MCD connected to the FOSTC fiber optic adaptor board s SAT RS-485 communication loop. Operator Interface 5
Fiber Optic Adapter Board Figure 4: The PL102334 FOSTC Fiber Optic Adapter Board Coupled to the FOSTC Serial to Fiber Optic Converter Figure 5: The PL102334 FOSTC Fiber Optic Adapter Board Shown in a Typical Application 6 Operator Interface
FOSTC Overview Fiber optic cabling has inherent resistance to EMI/RFI and transient immunity, making it ideal for industrial and utility data communication applications. The FOSTC was designed to provide the most versatile connection possible between any two-wire, RS-485 equipment using Fiber Optic cable. The FOSTC can be used for point-topoint communications between serial devices or in a multi-drop fiber ring configuration, allowing multiple serial devices to communicate with each other. The FOSTC allows any two pieces of asynchronous serial equipment to communicate full or half-duplex over two fibers at typical distances up to 2.5 miles (4 km). To extend the distance of the fiber link beyond 2.5 miles, use B&B model FOSTDRP Fiber Optic Repeater. 2 for typical point-to-point and multi-drop configurations. The most important consideration in planning the fiber optic link is the power budget of the fiber modem. This value represents the amount of loss in db that can be present in the link between the two modems before the units fail to perform properly. This value includes line attenuation as well as connector loss. For the FOSTC the typical connector-toconnector power budget is 12.1 db. Because 62.5/125 m cable typically has a line attenuation of 3 db per Km at 820 nm, the 12.1 db power budget translates into 2.5 miles. This assumes no extra connectors or splices in the link. Each extra connection would typically add 0.5 db of loss, reducing the possible distance by 166 m (547 ft.). The actual loss should be measured before assuming distances. The FOSTC uses a separate LED emitter and photo-detector operating at 820 nm wavelength. Connections to the emitter and detector are on ST type connectors. Almost any multimode glass fiber size can be used including 50/125 m, 62.5/125 m, 100/140 m, and 200 m. One fiber is required for each connection between a transmitter and receiver. In a point-to-point configuration, two fibers are required between the two modems, one for data in each direction. A multi-drop ring configuration requires one fiber between TX and RX around the loop. See Figure Operator Interface 7
WCC III System Overview Figure 6: Typical WCC III System Overview with the FOSTC Used to Connect a Second Building to the WCC III System 8 Operator Interface
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Form: WM-FBROPTICS-TGD-01A Printed in the USA February 2009 All rights reserved. Copyright 2009 WattMaster Controls, Inc. 8500 NW River Park Dr. Parkville, MO 64152 Phone (816) 505-1100 www.wcc-controls.com Fax (816) 505-1101