Pulse Input Source Module; Figure 3-16. Pulse Input Source Module Field Wiring - Emerson Fisher FLOBOSS 407 Instruction Manual

FloBoss 407 Instruction Manual

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.
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
terminals B and C, the opening and closing of the contacts causes current to either flow or not flow
between V and ground at terminal C.
s
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
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.
ROC-POWERED
PULSE DEVICE
Rev 5/00
CAUTION
. When a field device, such as a set of relay contacts, is connected across
s
I
R
W
TO OPTIMIZE SCALING RESISTOR R1:
V – 1
S
R1 =
I
R1 + R + 2.2K = LOOP RESISTANCE = 3.4K OHMS MAX
W
I = LOOP CURRENT = 5 mA TYPICAL
R = RESISTANCE OF FIELD WIRING
W
V = SOURCE VOLTAGE FROM MODULE = 11 TO 30 VDC
S

Figure 3-16. Pulse Input Source Module Field Wiring

N/C
A
+
B
–
C
– R – 2.2K
W
)
s
R1=10
PI SRC
V
2.2K S
3-19