INTRODUCTION

The Model 485T Tester can be used to check the condition of signals at any node on an RS-422 or RS-485 network. The tester determines if the maximum permissible negative or positive voltages are being exceeded. If these voltage levels are exceeded it is possible to damage the RS-422/485 receivers and drivers. The tester also checks to see if minimum required differential voltages exist on the lines. The tester uses the normal data that is transmitted on the line to check the value of the minimum differential voltage. There is an RS-232 output that can be used to view the network data.

RS-422 AND RS-485 STANDARDS

The RS-232 Standard (Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange) was developed many years ago by the Electronic Industries Association (EIA). It was used to connect modems to terminals for dial-up computer systems. Since the modem and terminal were usually located close to each other, wire length was not much of a factor in the standard. RS-232 maximum wire lengths were set at 50 feet. RS-232 lines can run farther with special (low capacitance) wire but there is a practical limit of 300 or so feet.

The EIA then developed two newer standards to allow serial data communications to go past the 50 foot barrier. The first is RS- 422, Electrical Characteristics of Balanced Voltage Digital Interface Circuits. The second is RS-485, Standard for Electrical Characteristics of Generators and Receivers for use in Balanced Digital Multipoint Systems. Using these standards, wire lengths of about 4000 feet are attainable. This is possible by using two wires for each signal instead of the one wire used in RS-232.

A typical RS-232 system can have eight wires, seven signals and one ground, not all of which are used in every system. As each signal goes high or low (typically +12 and -12 volts) it uses the one ground wire as a reference. Ground currents can cause confusion. Also, the RS-232 drivers are not capable of driving much more than 2500 picofarads before the signal on the line is badly distorted.

Both RS-422 and RS-485 use two wires for each signal. These two wires are driven differentially. When one wire is low the other is

Documentation Number 485T1995 Manual

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B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350

PH (815) 433-5100 --

FAX (815) 433-5105

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B&B Electronics 485T manual Introduction
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485T specifications

B&B Electronics has been a prominent player in the field of industrial connectivity solutions, and one of their notable products is the 485T. The 485T is a robust serial communication device designed specifically for converting RS-232 signals to RS-485. This device is particularly valuable in environments that necessitate reliable signal transmission over extended distances, which is where traditional RS-232 connections typically fall short.

One of the standout features of the B&B Electronics 485T is its ability to support communication over long distances of up to 4,000 feet. This makes it an ideal solution for applications in industrial settings, where distances between devices often exceed the limitations of standard serial connections. With data rates of up to 115.2 kbps, the 485T ensures that information can be transmitted swiftly and efficiently, making it suitable for various real-time monitoring and control applications.

The 485T incorporates advanced technologies that enhance its performance and reliability. For instance, it features built-in surge protection, which safeguards the device and connected equipment from voltage spikes and transient events. This is crucial in industrial environments where electrical noise and surges can be commonplace. Additionally, the device is designed to support multiple nodes on the RS-485 network, accommodating up to 32 devices simultaneously. This versatility allows for expanded networking capabilities, making it easier to integrate multiple devices and sensors into a cohesive communication system.

In terms of configuration, the B&B Electronics 485T is user-friendly, featuring jumper settings that allow for quick adjustments to accommodate different application requirements. Users can easily switch between half-duplex and full-duplex modes, providing greater flexibility based on the needs of their specific communication networks.

The 485T's compact design makes it easy to integrate into existing systems without taking up excessive space, and its durable construction ensures reliability in demanding environments. Furthermore, with a temperature range designed to withstand industrial conditions, the device can function effectively in both warm and cold settings.

In conclusion, the B&B Electronics 485T is a powerful solution for anyone in need of reliable and long-distance RS-232 to RS-485 conversion. With its high data rates, long-distance capabilities, and enhanced durability, the 485T serves as an excellent choice for industrial communication applications, ensuring that devices remain connected and operational even in the most challenging environments.
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