Hach ORBISPHERE G1100 User Manual page 105

Glossary
Master / Slave modes
Parallel communication
PLC
PROFIBUS-DP
PROFIBUS-DP
GSD files
Relative pressure
Resistivity
RS-232
RS-422
RS-485
Serial communication
Single twisted pair
USB
104
A device operating as a master will poll one or more devices operating as a slave. This means a
slave device cannot volunteer information; it must wait to be asked for it.
Parallel communication represents a connection in a computer system in which the bits of a byte
are transmitted over separate channels at the same time.
Programmable Logic Controller. It communicates with other process control components through
data links. It is used in process control for simple switching tasks, PID control, complex data
manipulation, arithmetic operations, timing and process and machine control.
The PROFIBUS-DP (Decentralized Peripheral) fieldbus is designed especially for communication
between automation control systems and distributed I/O at the device level. Each DP device has
specific parameters such as device version, baud rate, data format, I/O length, user parameters,
etc. These parameters are stored in a file with .GSD extension.
The GSD file is provided by the manufacturer and is required for device configuration. A GSD file
is a readable ASCII text file that contains both general and device-specific specifications for
communication (Communication Feature List) and network configuration.
Relative pressure is the over pressure in a system (i.e. absolute pressure less atmospheric
pressure). This is the customary gauge reading.
The opposition offered by a body or substance to the passage through it of a steady electric
current.
RS-232 is a serial communication standard providing asynchronous communication capabilities
with hardware flow control, software flow control, and parity check. Maximum transmission
distance is up to 15 meters at a max. 20,000 bps. A converter is required to interface RS-232 with
RS-422 or RS-485.
RS-422 is intended for point-to-point communications. It provides much longer transmission
distance but less signal line compares to RS-232. RS-422 adopts differential transmission
technology and thus provides high-speed transmission up to 10mbps and maximum transmission
distance up to 1.2km/110kbps.
RS-485 is an enhanced version of RS-422 and is used for multipoint communications, meaning
that many devices may be connected to a single signal cable. It is compatible to RS-422 interface
and provides 2 wire bus topology.
Serial communication represents a connection in a computer system in which the bits of a byte
are transmitted sequentially over a single wire.
In this version, all devices are connected to a single Twisted Pair. Thus, all of them must have
drivers with tri-state outputs (including the Master). Communication goes over the single line in
both directions. It is important to prevent more devices from transmitting at once (software
problem).
Universal Serial Bus. An external peripheral interface standard for communication between a
computer and external peripherals over a cable using bi-serial transmission. The USB host uses a
type A connector.