Jump up to main page of Converters to see prices: click here
J990
RS232 to 20mA loop isolated interface.
Opto-isolated, bidirectional, duplex 4-wire or simplex 2-wire I loop.
Supports up to 19Kkbps or more, the supported data speed depends on the line length and quality.
Allows communications up to 1Km or more,
with protection from ground currents and accidental connections to high voltage.
At the far end the loop can be driven by another STD-990 for isolation at
that end, or by a JED 3-slot motherboard power supply.
A plug-pack at one
end can provide isolated loop power for both directions.
Case: 25x50x100mm.
Incl 16 way (2x8) cnnctr & ribbon cable.
Interconnects
RS232 systems (e.g. a PC) to industrial systems (e.g. PLC) via the 20mA loop standard.
Loop current flows in normal state (broken by TX byte, giving a security alarm
if line broken (overrun error in communications software).
Isolation rated at 2,500 volts.
Allows multi-dropping with a number of stations connected in series with no special TX ‘‘connect-to-line’’ control software needed.
RX can monitor transmission on line, so verifying transmission is actually happening on the serial network.
This device is designed with five functions in mind:
1.
To extend the common RS232 communication standard to distances of 1 Km. or more.
2. To eliminate the problem of ground currents and common mode voltages which
can exist between the
grounds of electronic equipment separated by distance,
especially in industrial or rural-agricultural applications of computers.
3. To totally protect the computing or data logging equipment at both ends of a data link from accidental connection of one or more signal connections between equipment to a high voltage, e.g. 240 volt mains or surges induced by lightning.
4. To allow connection between existing 20-mA interface equipped systems and RS232C
connections on JED
or other control computers, or PC’s from any source,
which usually have RS232C only communication facilities.
5. This device is particularly useful in interfacing Programmable Logic Controllers to PC’s.
Data Path.
RS232 data is
fed through a Hewlett Packard HCPL4100 current loop transmitter/isolator.
Both terminals of this driver are available on screw terminals on the isolated
side.
20 mA loop current passes through the LED of a 20 mA opto-isolator
receiver (HCPL4200) and the
output is converted back to RS232 data.
The
RS232 connections are two rows of stake pins configured in such a way that a ribbon
cable can mate directly with a D25 connector as a DTE or DCE device.
Loop Power Supply.
There is no electrical connection
between the RS232 and the 20 mA sides,
so power for the loop cannot come
from the RS232 system.
Power for the RS232 output is actually generated from
the RS232 signals themselves.
A simple bridge rectifier
and filter capacitor with two 20 mA active current sources is provided for the
transmit and receive loops.
This power supply is normally fed with a 12-15
volt AC or DC signal from a double insulated plug pack which is available as an
option.
Loop power is normally provided to a system for both transmit and
receive loops from one end of a system and so one plug pack can power both loops
and is needed at only one end.
Performance is quoted by HP at 20 KBaud data
rate at 400 metres.
Curves shown on the data sheets show a linear relationship
between speed and line length.
Induced noise isolation is excellent, even
with unscreened cables, although in extreme cases shielded cables could help.
However performance is many times better than an RS232 system
with the
added advantage of complete isolation of the wiring from the computers at either
end.
External power supply, isolated, 9 to 12 VDC required
PAK9 plug pack mains adaptor 240VAC to 9VDC: $20+GST