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FloBoss 407 Instruction Manual
Rev 5/00
3-19
3.4.10 Pulse Input Source Module
A schematic representation of the field wiring connections to the input circuit of the Pulse Input
Source module is shown in Figure 3-16.
CAUTION
The Pulse Input Source module is designed to operate only with non-powered
discrete devices such as “dry” relay contacts or isolated solid-state switches. Use of
the module with powered devices may cause improper operation or damage to
occur.
The Pulse Input Source module provides a voltage across terminals B and C that is derived from
internal voltage source V
s
. When a field device, such as a set of relay contacts, is connected across
terminals B and C, the opening and closing of the contacts causes current to either flow or not flow
between V
s
and ground at terminal C.
This interrupted, or pulsed current flow is counted and accumulated by the PI Source module which
provides the accumulated count to the ROC/FloBoss electronics upon request.
A 10-ohm scaling resistor (R1) is supplied by the factory and accommodates a source voltage (V
s
)
of 11 to 30 volts dc and a pulse source with a 50% duty cycle. The source voltage is the input voltage
to the ROC/FloBoss. 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 3-16. For optimum efficiency, R1should be scaled
for a loop current (I) of 5 milliamps.
PULSE DEVICE
ROC-POWERED
V
S
= SOURCE VOLTAGE FROM MODULE = 11 TO 30 VDC
R1 + R
W
+ 2.2K = LOOP RESISTANCE = 3.4K OHMS MAX
– R
W
– 2.2K
R
W
= RESISTANCE OF FIELD WIRING
TO OPTIMIZE SCALING RESISTOR R1:
I = LOOP CURRENT = 5 mA TYPICAL
R1 =
I
I
R
W
V
S
– 1
B
C
–
A
N/C
+
R1=10
2.2K
PI SRC
V
S
Figure 3-16. Pulse Input Source Module Field Wiring
Содержание Fisher FLOBOSS 407
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