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RF Modules Implement Turnkey Wireless Data Collection

The manufacturer says . . .

ChipCenter's Alex Mendelsohn says . . .

The RF Neulink RF9600 Wireless modem is designed for ease of use and flexibility of operation. Flow control, I/O data rate, packet size, and many other features may be reconfigured to meet specific system needs. The desired configuration and address ID are programmed via the serial port and are stored in memory. Data in and out of the unit need not be in any particular format, as each byte entering will be properly transmitted and then received at the far end. No padding characters are required, and no "dribble bits" will come out of the receiving unit. Even though data are sent in packets, the user will see a transparent link, with each byte going in one end and coming out the far end. Hardware or software flow control can be enabled for serial I/O speeds of up to 57.6 kbits/s. Transmitted packets are formatted automatically within the RF9600, which adds and later removes source and destination addresses and CRC detection code. For point to multi-point operation, where address determination is done by each remote modem, the model RF9600B "Base Modem" is used. The RF9600B allows the central computer to address each specific modem individually by preceding data streams with a destination address. The range can be increased with the addition of a store and forward RF9600 or a fast switching external power amplifier. Frequency Ranges 136–150 MHz 150–174 MHz 403–416 MHz 416–430 MHz 430–450 MHz 450–470 MHz 470–480 MHz 488–496 MHz 496–512 MHz

These 9,600 bits/s Gaussian frequency-shift-keyed (GFSK) modules are made by the Neulink Division of RF Industries. RFI is a company that's been dishing up wireless data systems for SCADA applications (System Control and Data Acquisition), as well as other RF modems and two-way radios, for over twenty years. As such, you can benefit from company expertise, as well as a product line including complementary products, such as higher speed systems and even antennas. In line with the company's industrial background, one of the first things on the spec sheet that caught my eye were temperature ratings. The spec sheet shows a -30°C to +60°C range for these modules. Unlike many 0–70°C products, that means the RF9600s should work reliably in almost any industrial environment—even outdoors with the addition of a suitable weatherproofed enclosure. Intelligent Packages Integrating digital and analog transceiver functions in one microprocessor-based frequency-synthesized package, an RF9600 develops two watts of RF at its 50 W antenna output jack. The operating power is from 12 V sources, where the modules draw about 150 mA while receiving, jumping to about 750 mA when transmitting a packet. The cost per module is a bit less than $600. Lamentably, Neulink encapsulates your data in a proprietary protocol packet, so RF9600 boxes can only be used with other Neulink RF systems. Protocol issues aside, RF9600s are quite programmable, supporting multi-point addressing with more than 65,500 different addresses. That permits you to establish an RF network containing a number of these boxes, within practical limitations of topology, addressing, and overhead. Note that these modules can be ordered in a number of frequency bands between 136 MHz and 512 MHz, but some parts of this covered spectrum are allocated to other services, both commercial and amateur. Neulink clearly states that it's your responsibility to place these modules appropriately and to obtain proper FCC licensing, so take heed. Also, the modems comply with Part 15 of the FCC rules and regulations, and as such must not be modified without special permission. Store-and-Forward Networking Each RF9600 can also store and forward data from other units in order to fill in RF blind spots, or to extend range. The hex addressing scheme for this even permits you to create sub-nets. However, there may be hidden nodes in such a configuration, possibly causing latencies due to lack of collision detection. Indeed, Neulink recommends not using these boxes in wide-area networking schemes. On the host side, individual RF9600 modems can route data asynchronously either through TTL interfaces to a computer or other system, or via an RS-232 serial I/O line. Although the raw data rate at the RF layer is 9,600 bits/s, the async side can operate at speeds to 57 kbits/s. Flow control on an RS-232 connection, if desired, can be established using either hardware or software handshaking. You can even hitch one of the boxes to a landline modem to extend an RF network into the wired domain. Command String Programming You set up one of these modems using simple command strings through nothing more elaborate than an ASCII terminal or terminal emulator, such as the venerable DOS-hosted ProComm program. Asymmetrical data rates are also supported—the serial I/O rate of each RF9600 in a network can be programmed independently, permitting two RF9600s with different asynchronous port data rates to communicate with each other across the same RF path. At the RF level, the RF9600 modules handle all link data-flow management tasks, relaying packets transparently from one RF9600 to another. In most cases, all you need do is program an RF9600 with the correct operating frequencies if they're different from the preprogrammed default frequency. You then insert an address, and the unit is ready to send and receive RF packets. Bt, there are two layers of addressing in an RF9600 system, a feature that supports millions of I/Os to be addressed individually. The top layer of addressing is done in the modems themselves, where each unit's 16-bit ID identitifes it in the RF network. Beyond that, each modem can have up to eight I/O modules stacked on it, each with its own address that's set with a rotary switch. Neulink offers a wide variety of these I/O modules, as well as integrated products. The company's RF Neulink SLM, for example, comprises an RF Neulink RF9600 modem that's interfaced with up to eight stackable I/O control modules. Each I/O module provides the electrical interface for monitoring and control functions. Modules range from relay-output types to optically isolated I/Os, and analog-input types. The latter include on-board 8-bit data converter chips and integral supply-voltage measurement hooks for remotely monitoring a Neulink module's voltage. Remote terminal units (RTUs) and so-called SLM modules also provide a mimic mode (note that the Neulink SLM RTUs are essentially preconfigured with I/O modules. The turnkey offering already has a top cover removed, a ribbon cable installed, and an RF module attached). In mimic mode, an RTU slaves one unit's multiple I/Os to another unit's corresponding I/Os. Two Neulink SLM RTUs can therefore be used interactively to control and monitor remote devices from a central location—without needing a PC or external radio. In a mimic-mode application, a remote SLM's multiple I/Os can be used to sense and control external electro-mechanical devices, and another SLM can be at a central monitoring location with its I/Os interfaced to indicators that display status. It can also be interfaced to switches that can activate remote devices. Mix and Match Modules To its credit, Neulink offers a nice mix of modules. The firm's Model SLM-A, for example, is an I/O module with eight optically isolated (500 V) and jumper-defined I/Os. It also includes an 8-bit analog input that can accommodate signals over a range from 0–5 V (input impedance is greater than 10 kW). Shown on the company's Web page, the SLM-A module's open-collector outputs only handle to 5 mA. As such, the SLM-A has been discontinued, and is superseded by the SLM-B version. The -B spin is essentially an identical I/O module, but it has a higher current handling spec than its -A cousin had. Its open-collector outputs use Darlington transistors that permit sinking up to 100 mA. The SLM-B costs about $180. A $150 Model SLM-C is available for precision work. It's a dual analog-I/O module; its two inputs and two outputs use 12-bit A/D converters and D/A converters that provide 0.5 percent absolute accuracy. For power hefting to 125 W, Neulink offers a Model SLM-D four-channel relay module. Priced at $195, and equipped with four sets of Form C (SPDT) relays, it can switch up to 5 A at 30 V DC or 250 V AC (max). A Model SLM-E relay module also offers four channels of Form C relay switching, but it uses latching relays. Its latched coils draw current only during status changes, saving current demand. The SLM-E is priced at $210. The relay life on either of these modules is rated for at least one million closures. For more details, contact Neulink 7610 Miramar Rd. San Diego, Calif. 92126 Phone: (858) 549-6340     or (800) 233-1728 FAX: (858) 549-6349 Web: www.rfneulink.com

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