Yokogawa Standalone MW100 - Manual (Page 115)

2-27 IM MW100-01E
Installation and W
iring
1
2
3
4
5
App
Index
Note
• The noise rejection method differs depending on the conditions of use. In the connection
example, the cable shielding is only connected to the ground of the main unit (one-sided
grounding). This method is effective for noise rejection during long distance communications
and other processes when there is a difference of potential between the grounding of the
computer and that of the main unit. If there is no difference in potential between the PC
ground and the main unit ground, it may also be effective to connect to the PC ground
as well (two-sided ground). There are also cases where it is effective to use two sided
grounding with a capacitor connected in series on one side. Consider the above options
when taking measures against noise.
• With the 2-wire configuration (Modbus protocol), after the last data is output from the
upstream PC, the 485 driver must be set to high impedance before 3.5 characters.
Serial Interface Converter
The following are recommended models of converters.
Sysmex RA CORP./MODEL RC-770X, LINE EYE/SI-30FA, YOKOGAWA/ML2
CAUTION
Some converters not recommended here have non-insulated FG and SG
terminals. When using such converters, do not connect them as shown on the
previous page (do not connect anything to the converter’s FG ad SG terminals).
Especially for long-distance situations, potential differences can arise causing
damage to instruments or communication abnormalities. Also, if the converter
has no SG terminal, use the converter as-is without connecting signal ground.
For details, see the user’s manual for the converter.
Some converters not recommended here have reversed signal polarity (A/B or +/–
markings). When using such converters, be sure to reverse the connections.
When Using Instruments That Only Support RS-422A
For 4-wire configurations, up to thirty-two MW100s can be connected to a single
upstream device. However, if at least one of the devices in the system only supports RS-
422A, it may not be possible to connect up to thirty-two units.
When Using Recorders That Only Support Yokogawa RS-422A
The maximum number of units that can be connected in this case is sixteen. Drivers for
some conventional Yokogawa recorders (the HR2400, µR series, and other recorders)
only support RS-422A. When such recorders are used, only a maximum of sixteen units
can be connected.
Note
In the RS-422A standard, up to ten units can be connected to a single port (in 4-wire configurations).
Termination Resistance
This module has built-in termination resistance. When using multi-drop connections
(including point-to-point connections), for the outermost unit, turn terminator switch ON.
Turn it OFF for units in the middle. Also, turn ON termination resistance for the connected
upstream device (see the manual of the upstream device). When using a converter, turn
ON its termination resistance. The recommended converters have built-in termination
resistance.
2.7 Connecting the RS-422A/485 Interface (/C3 Option)