ScreenMaster RVG200
Paperless recorder
3 Installation
OI/RVG200-EN
21
3.7 Relays
One relay is provided as standard (position F). An additional relay module can be fitted in positions A, B, C
or D to provide 6 additional relays per module.
The maximum individual relay current is 5A. The total load for all relays within the recorder must not exceed
36 A.
Relay contacts are fitted with arc suppression components as standard.
3.8 MODBUS module
A MODBUS module can be fitted internally to the power supply board in position E to provide a 2- or 4-wire
isolated RS485 interface.
3.8.1 Host computer serial communications
The serial interface option module uses the MODBUS Remote Terminal Unit (RTU) Master / Slave protocol.
An appropriate RS422 / 485 communications driver must fitted to the host (Master) computer. It is strongly
recommended that the interface has galvanic isolation to protect the computer from lightning damage and
to increase signal immunity to noise pick-up.
3.8.2 2- or 4-wire connection
MODBUS serial communications must be configured as 2-or 4-wire serial links – see Figs 3.9 and 3.10,
respectively. The recorder must be added to the link configuration on the host system – refer to information
supplied with the host system.
Fig. 3.9 2-wire connection
8
9
10
11
12
13
Terminal block E
Host computer
Rx/Tx +
Rx/Tx –
COM
GND
1.8 k
pull-up resistor
1.8 k
pull-down resistor
Tx +
Tx –
Rx +
Rx –
0 V
+5 V
'B'
'B'
'A'
'A'
GND
