Emerson Fisher FLOBOSS 407, Инструкция по эксплуатации

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FloBoss 407 Instruction Manual
3-20 Rev 5/00
3.4.11 Pulse Input Isolated Module
A schematic representation of the field wiring connections to the input circuit of the Pulse Input
Isolated module is shown in Figure 3-17.
NOTE
The Pulse Input Isolated module is designed to operate only with discrete
devices having their own power source such as “wet” relay contacts or
two-state devices providing an output voltage. The module is inoperative with
non-powered devices.
The Pulse Input Isolated module operates when a field device provides a voltage across terminals B and
C of the module. The voltage sets up a flow of current sensed by the module. When the field device no
longer provides a voltage, current stops flowing.
This interrupted, or pulsed current flow is counted and accumulated by the PI module which provides
the accumulated count to the ROC/FloBoss electronics upon request.
A 10-ohm scaling resistor (R1) is supplied by the factory, which accommodates a field device with
pulse amplitude (Vo) of 11 to 30 volts dc and a duty cycle of 50%. However, it is desirable to optimize
the value of R1 to reduce the current drain from the source or reduce the heat generated in the module
due to amplitudes greater than 30 volts dc. The formula for determining the value of R1 is given in
Figure 3-17. For optimum efficiency, R1 should be scaled for a loop current (I) of 5 milliamps.
+
–
SELF-POWERED
PULSE DEVICE
R
W
= RESISTANCE OF FIELD WIRING
V
O
= VOLTAGE FROM PULSE DEVICE = 11 TO 30 VDC
R1 + R
W
+ 2.2K = LOOP RESISTANCE = 3.4K OHMS MAX
– R
W
– 2.2K
TO OPTIMIZE SCALING RESISTOR R1:
I = LOOP CURRENT = 5 mA TYPICAL
R1 =
V
O
V
O
– 1
I
R
W
C
B
+
–
A
N/C
DOC0149A
R1=10
2.2K
PI ISO
Figure 3-17. Pulse Input Isolated Module Field Wiring