Yokogawa EJX440A - Manual (Page 8)

IM 01C25T03-01E 2-1
2. CONDITIONS OF COMMUNICATION LINE
2. CONDITIONS OF COMMUNICATION
LINE
The BRAIN communication signal is superimposed
onto the 4 to 20 mA DC analog signal. Since the
modulated wave is a communication signal, superim-
posing it on the normal signal will, from basic prin-
ciples, cause no error in the DC component of the
analog signal. Thus, monitoring can be performed via
the BT200 while the transmitter is on-line.
2.1 Connecting the BT200
Connection to the transmitter with the BT200 can be
made by either connecting to the BT200 connection
hooks in the transmitter terminal box or by connecting
to a relaying terminal or a terminal board.
Relaying
terminals
Distributor
Control room
Terminal board
F0201.EPS
SUPPL Y
PU LS E
CHECK ALARM
Figure 2.1 Connecting the BT200
2.2 Communication Line Re-
quirements
DPharp
BT200
Cable
resistance Rc
Cable resistance Rc
Load
resistance R
cc
Power
supply
᭹ Loop resistance = R + 2Rc
= 250 to 600
Ω
᭹ Loop capacitance = 0.22
µ
F max.
F0202.EPS
Figure 2.2 Communication Line Requirements
2.3 Power Supply Voltage and
Load Resistance
When configuring the loop, make sure that the external
load resistance is within the range in the figure below.
(Note) With an intrinsically safe transmitter, external load resistance
includes safety barrier resistance.
600
250
0 10.5 16.6 25.2 42
External
load
resistance
R (
Ω
)
Power supply voltage E (V DC)
F0203.EPS
Communication
applicable range
R=
E–10.5
0.0244
Figure 2.3 Relationship between Power Supply Voltage
and External Load Resistance