Yokogawa DR240 - Manual (Page 25)

3-6 IM DR231-11E
Converter
Recommended converter : Sharp Z-101HE
Caution
Some converters other than the recommended, do not have the FG and SG termi-
nals insulated. In such cases, do not connect as in the diagram on the previous
page (do not connect anything to the FG and SG terminals of the converter). Es-
pecially when it is long distance, the potential difference may damage the devices
or the communication may become unreliable.
Also, converters without the SG terminal can be used without grounding. For
details, refer to the converter’s manual.
Some converters other than the recommended have their signal polarity reversed (indication of A/B
or +/-). In this case, reverse the connection. If the “RD” LED on the front panel of the RS-422-A/
RS-485 module blinks when it receives data, the connection is correct. If it lights, the connection
may be reversed.
In the case of the two-wire system, the host computer must control the ON/OFF of the transmission
driver of the converter in order to prevent the collision of the send and receive data. When using the
recommended converter, ON/OFF is controlled using RTS.
Using the Module with Devices Using the RS-422-A
Maximum of 31 devices with respect to 1 host computer can be connected with this module, but in
a system in which devices using the RS-422-A are used together, this may not be possible.
• In a system in which former Yokogawa recorders are used together
Some of the former Yokogawa recorders (such as HR2400 and
µ
R) use the RS-422-A driver. In
this case, the maximum number of devices that can be connected is 16.
Note
• According to the RS-422-A standard, the maximum number of devices that can be connected with respect to one port is 10
devices (in the case of a four-wire system).
Terminator
When devices are connected in multi-drop configuration (includes point-to-point connections), turn
the terminators of the modules on the extreme ends ON. All modules in between should have them
turned off. Terminators are turned ON/OFF using the TERMIN switch on the front panel.
Also, turn ON the terminator on the host computer (refer to the computer’s manual). When convert-
ers are used, turn their terminators ON also. The recommended converter needs an external termi-
nator to be installed, but some converters are internal types.
3.3 RS-422-A/RS-485 Interface Connection