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ADA-1020
2.2. DESCRIPTION
ADA-1020 converter is a device used to convert the RS232 to current loop standard without interfering with the format of transmitted
data and does not require the power supplying from the RS232 port. The converter supports RS232 asynchronous data transmission
at baud rate up to 38.4 kbps via two pairs of twisted-pair cable.
ADA-1020 is equipped with one female DB-9F connection to connect RS232 interface and screw terminal block for connection of
Current Loop bus and power supply. Connector DB-9F RS232 interface is made like DCE, it let connect converter to computer in use
the typical extension cable RS232 (cable for modem connection) without crossing Tx with Rx and RTS with CTS.
Converter uses signals Rx, Tx and GND for operating, which are entered via DB-9F connector. RTS signal is looped with CTS and
DTR with DSR and DCD inside the converter. Other signals are not connected.
You can connect to the Current Loop line two ADA-1020 converters operates in full duplex or half duplex mode in point-to-point
topology.
RS-232 interface
DB-9F connector
(RS-232)
ADA-1020
RS-232 to CURRENT LOOP
CONVERTER
RX
TX
CL
(CURRENT LOOP)
Current Loop
Interface
53mm
Version with active transmitter +/- 20mA
2.3. CURRENT LOOP TRANSMITTER
The Current Loop transmitter at ADA-1020 is made as:
- active, on the base power source generate current +/- 20mA or 0-20mA (depend on converter's version). The transmitter has short
circuit protection on TX+ and TX- lines.
- passive 0-20mA, on the base transistor, has also short circuit protection on TX+ and TX- lines.
The transmitter of Current Loop 0-20mA can work as ACTIVE or Passive, the selection is made by the TX switch on the front panel
(see Fig.1).
The passive transmitter can be used only for creation of current loop bus, see point 3.5.
The diagram of the transmitter & receiver is shown on figure below.
2.4. CURRENT LOOP RECEIVER
In the ADA-1020 converter has been used passive RX receiver consisting of optoisolator (optical coupler) and protective elements.
The receiver circuit has RX+, RX- terminals as well as the terminal marked as RX-*. In the circuit with RX-* terminal has been used
additional resistor (1000 ohms or 560 ohms depend on the converter version) to reduce power in the case of connecting the receiver
to transmitter which has NOT short circuit current limit to 20mA.
The RX red LED on front panel of the converter is a signalization of NO current flow through optocoupler. This LED is ON when it is:
- not connect transmitter to receiver,
- wrong connection of transmitter to receiver,
- broken connection of transmitter to receiver.
The diagram of the transmitter & receiver is shown on figure below.
PWR
10 – 30
VDC
Power supply
10-24-30 VDC
Version with active / passive transmitter 0 / 20mA
Fig 1. View of the ADA-1020
RS-232 interface
DB-9F connector
(RS-232)
ADA-1020
RS-232 to CURRENT LOOP
CONVERTER
ACT
PSV
RX
TX
PWR
TX
CL
(CURRENT LOOP)
10 – 30
VDC
Power supply
10-24-30 VDC
Current Loop
Interface
4
62mm
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