FloBoss 407 Instruction Manual
3-22
Rev 5/00
3.4.13 Slow Pulse Input Isolated Module
A schematic representation of the field wiring connections to the input circuit of the Slow Pulse Input
Isolated module is shown in Figure 3-19.
NOTE
The Slow 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 Slow 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, which signals the
ROC/FloBoss electronics that the field device is active. When the field device no longer provides a
voltage, current stops flowing and the SPI module signals the ROC/FloBoss electronics that the device
is inactive. The ROC/FloBoss software counts the number of times the current starts flowing, and
stores the count. The software checks for the input transition every 50 milliseconds.
A 10-ohm scaling resistor (R1) is supplied by the factory, which accommodates an external voltage
(V
o
) of 11 to 30 volts dc. 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 high source voltage. The
formula for determining the value of R1 is given in Figure 3-19. For optimum efficiency, R1 should be
scaled for a loop current (I) of 3 milliamps.
+
-
DISCRETE
DEVICE
SELF-POWERED
V = VOLTAGE FROM DISCRETE DEVICE = 11 TO 30 VDC
R1 + R
+ 3.3K = LOOP RESISTANCE = 4.5K OHMS MAX
R = RESISTANCE OF FIELD
I = LOOP CURRENT = 3 mA TYPICAL
o
w
- R - 3.3K
TO OPTIMIZE SCALING RESISTOR R1:
R1 =
V
O
V - 1
o
I
R
W
w
C
B
A
+
-
N/C
DOC0152A
SPI ISO
3.3K
R1=10
I
w
Figure 3-19. Slow Pulse Input Isolated Module Field Wiring
Содержание Fisher FLOBOSS 407
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