Figure 3-18. Slow Pulse Input Source Module Field Wiring - Emerson Fisher FLOBOSS 407 Instruction Manual

FloBoss 407 Instruction Manual
3.4.12 Slow Pulse Input Source Module
A schematic representation of the field wiring connections to the input circuit of the Slow Pulse Input
Source module is shown in Figure 3-18.
The Slow 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 Slow Pulse Input source module operates by providing a voltage across terminals B and C
that is derived from internal voltage source V
is connected across terminals B and C, the closing of the contacts completes a circuit, which causes a
flow of current between V
This current flow is sensed by the SPI module, which signals the ROC/FloBoss electronics that the
relay contacts have closed. When the contacts open, current flow is interrupted and the SPI module
signals the ROC/FloBoss electronics that the relay contacts have opened. The ROC/FloBoss software
counts the number of times the contacts switch from open to closed, 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 that accommodates a source voltage (V
11 to 30 volts dc. The source voltage is either the input voltage to the ROC/FloBoss or the output
voltage of the I/O converter card if one is installed (ROC364 only). 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-
18. For optimum efficiency, R1 should be scaled for a loop current (I) of 3 milliamps.
ROC-POWERED
DISCRETE DEVICE

Figure 3-18. Slow Pulse Input Source Module Field Wiring

Rev 5/00
CAUTION
. When a field device, such as a set of relay contacts,
s
and ground at terminal C.
s
I
R w
TO OPTIMIZE SCALING RESISTOR R1:
V - 1
s
R1 = - R
w
I
R1 + Rw + 3.3K = LOOP RESISTANCE = 4.5K OHMS
I = LOOP CURRENT = 3 mA TYPICAL
R = RESISTANCE OF FIELD
w
V = SOURCE VOLTAGE FROM MODULE = 11 TO 30 VDC
s
N/C
A
+
B
-
C
- 3.3K
) of
s
R1=10
SPI SRC
V
3.3K s
DOC0151
Modified
3-21