Каталог Weidmuller: Electronics - Analogue Signal Conditioning

Technical appendix/Glossary
Glossary
EIA-232/ RS232
EIA-422/ RS422
EIA-485/ RS485
Electrical equipment
Explosion groups
The term EIA-232 (originally RS-232) refers to a serial interface standard developed
by a U.S. standards committee (now known as the EIA – Electronic Industries
Alliance) in the early 1960s. EIA-232 specifies the connection between the data
terminal equipment (DTE) and the modem (data communication equipment or DCE).
It defines timing, voltage level, plug and protocol details. EIA-232 defines a voltage
interface. The information bits are encoded using electrical voltage. The data lines
(TxD and RxD) use a negative logic whereby a voltage level between -3 V and
-15 V (ANSI/EIA/TIA-232-F-1997) represents a logical one and a voltage level
between +3 V and +15 V represents a logical zero. Signal levels between -3 V and
+3 V are undefined.
EIA-422 (also known as RS-422) is an interface standard for cable-based differential,
serial data transmission. In contrast to the asymmetric serial interface specified by
the EIA-232 standard, the EIA-422 interface is designed for symmetric
transmissions. This means that two sets of twisted pair wires are required to carry
the positive and negative signals from the sender to the receiver. This minimises
common-mode interferences and also increases the data rates in comparison to the
asymmetric EIA-232 interface. EIA-422 can be used to establish a full-duplex,
point-to-point connection. Multi-drop networks with one sender and up to ten
receivers are also possible. The sender and receiver in multi-drop networks can
only be operated in half-duplex (in one direction). Because of the high data rate
(up to several MBit/s), a wire pair on the EIA-422 interface must be terminated with
a terminating resistor (normally 120 ohm).
EIA-485, also referred to as RS-485, is an interface standard for digital, cablebased,
differential, serial data transmissions. EIA-485 uses a wire pair for transmitting
inverted and non-inverted levels for a single-bit data signal. The original data signal is
reconstructed by the receiver as the difference between the two voltage levels. This
has the advantage of increasing the resistance to interference, since common-mode
interference then has no effect on the transmission. The EIA-485 interface operates
with a voltage differential of +/-200 mV, so that the voltage interface has a differential
related to half of the operational voltage. It normally uses a single wire pair and is
operated in half-duplex. However full-duplex operations are possible with two wire
pairs.This connection has multi-point capabilities; up to 32 nodes can be connected
to an EIA-485 bus. Standard cable lengths run up to 1.2 km in length and support
transmission speeds up to 10 MBit/s. The wire pairs must be terminated with
resistors (typically 120 Ohm) because of the cable length and high data rates.
All of the electrical and electronic components and circuits within an enclosure.
Depending on the ignition protection, explosion-protected equipment intended for
gases, vapours and mists are divided into three explosion groups (IIA-IIB-IIC).
The explosion group provides a measure of the explosive break-though capability of
gases (in an explosive atmosphere). The requirements for the equipment increase in
strictness from II A to II C.
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