Yokogawa Removable Chassis DX1000N - Manual (Page 103)

2-9
IM 04L41B01-17E
Using the Serial Interface
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2
3
4
5
6
App
Index
Note
• The method used to eliminate noise varies depending on the situation. In the connection
example, the shield of the cable is connected only to the DX’s ground (one-sided grounding).
This is effective when there is a difference in the electric potential between the computer’s
ground and the DX’s ground. This may be the case for long distance communications. If there
is no difference in the electric potential between the computer’s ground and the DX’s ground,
the method of connecting the shield also to the computer’s ground may be effective (two-sided
grounding). In addition, in some cases, using two-sided grounding with a capacitor connected
in series on one side is effective. Consider these possibilities to eliminate noise.
• When using the two-wire interface (Modbus protocol), the 485 driver must be set to high
impedance within 3.5 characters after the last data byte is sent by the host computer.
Serial interface converter
The recommended converter is given below.
SYSMEX RA CO.,LTD./MODEL RC-770X, LINE EYE/SI-30FA, YOKOGAWA/ML2
CAUTION
Some converters not recommended by Yokogawa have FG and SG pins that are not
isolated. In this case, do not follow the diagram on the previous page (do not connect
anything to the FG and SG pins). Especially in the case of long distance communications,
the potential difference that appears may damage the DX or cause communication errors.
For converters that do not have the SG pin, they can be used without using the signal
ground. For details, see the manual that comes with the converter.
On some non-recommended converters, the signal polarity may be reversed (A/B or +/-
indication). In this case, reverse the connection.
For a two-wire system, the host device must control the transmission driver of the
converter in order to prevent collisions of transmit and received data. When using the
recommended converter, the driver is controlled using the RS (RTS) signal on the
RS-232.
When instruments that support only the RS-422 interface exist in the
system
When using the four-wire system, up to 32 DXs can be connected to a single host device.
However, this may not be true if instruments that support only the RS-422 interface exist
in the system.
When YOKOGAWA’s recorders that support only the RS-422 interface exist
in the system
The maximum number of connection is 16. Some of YOKOGAWA’s conventional
recorders (HR2400 and µR, for example) only support the RS-422 driver. In this case,
only up to 16 units can be connected.
Note
In the RS-422 standard, 10 is the maximum number of connections that are allowed on one
port (for a four-wire system).
Terminator
When using a multidrop connection (including a point-to-point connection), connect a
terminator to the DX if the DX is connected to the end of the chain. Do not connect a
terminator to a DX in the middle of the chain. In addition, turn ON the terminator on the
host device (see the manual of the host device). If a converter is being used, turn ON its
terminator. The recommended converter is a type that has a built-in terminator.
Select the appropriate terminator (120 Ω), indicated in the figure, according to the
characteristic impedance of the line, the installation conditions of the instruments, and so on.
2.3 Connecting the DX