Service manual

B - 49
Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 2.0
Appendix B • Vission 20/20 Application Procedures
Phoenix Contact PSM-ME-RS485/
RS485-P Isolator
The Phoenix Contact isolator/repeater is used to electri-
cally isolate the RS485 signal from the network and to
improve the signal strength of the RS485 signal over
long distances. It has the added benefi t of active noise
suppression since it regenerates the active signal in rela-
tion to time and amplitude. Therefore, any noise on the
signal lines into the device will not be passed through
the device onto the network. The following test shown
in Figure B-25 was setup and performed to measure the
benefi ts of the isolator on an RS485 serial network run-
ning Modbus RTU protocol.
NOTE
The Phoenix Contact PSM-ME repeater was powered
from the +24vDC supply from the Vission 20/20
panel in this test.
t TERMINATION RESISTORS FOR
A&B ARE ON.
t SELECT BAUD RATE SWITCHES
TO MATCH NETWORK SPEED
PHOENIX CONTACT REPEATER
(PSM - ME - RS485/RS485-P)
SUPPLY POWER +24 VDC OR AC
VISSION 20/20
P12
JP2
(NOTE: LABELING
CONVENTION OF A & B
TERMINALS PER MAXIM,
WHICH IS IN CONFLICT OF
EIA-485 SEPCIFICATION)
TEK 2014
PROBE 1 PROBE 2
USB/RS485
“B” LINE IS POSITIVE
(COMPARED TO “A”)
WHEN LINE IS IDLE
-A
+B
GND
A
B
GND
SHD
GND
B
A
A
B
PORT A PORT B
Figure B-26. Phoenix Contact PSM-ME Isolator Test