Cameron NUFLO MC-III EXP, Руководство пользователя

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MC-III™ EXP Flow Analyzer Section 2
Analog (4-20 mA) Rate Output
The 4-20 mA rate output provides a linear current output that represents flow rate. This output requires a two-
conductor cable connected to an 8 to 30 VDC power supply (voltage required is dependent on loop resistance)
and a current readout device located in the remote location. The 4-20 mA rate output current loop also powers
the MC-III EXP. The internal battery (lithium or alkaline) provides a power supply backup to maintain
timekeeping accuracy and to continue accumulating volume in the event that the 4-20 mA current loop fails.
Figure 2.14 shows the minimum required voltage to power the instrument for a given loop resistance. In
addition, the mathematical relationship between loop voltage and load resistance is given. For example, if a
power supply voltage of 24 volts is available to power the current loop, the maximum load resistance would
be 800 ohms.
Caution: The 4-20 mA rate output and the flowmeter frequency output circuits are not isolated
from each other and cannot be used simultaneously. When the 4-20 mA output option is
used, do not connect external power to TB3.
For information on configuring the 4-20 mA rate output with the keypad, see Configuring the Rate Display,
page 35
. For information on configuring the 4-20 mA rate output with the interface software, see
4-20 mA
Output, page
66
.
TB1
PU
LS
E
IN
PU
T
RE
SE
T
IN
PU
T
TF
M
A&S
GND
TB
3
EXT POWER
TB2
RS
485
SL
AV
E
4-2
0
OU
T
PU
LS
E
OU
T
6-3
0 V
DC
J1
J2
RESET
SWITCH
BA
TT
ER
Y
POWER SUPPLY
8 to 30 VDC
LOAD
Resistor may be
included in readout
device.
4-20 mA and
flowmeter frequency
(amp & square)
cannot be used
simultaneously.
*
*
LOOP SUPPLY VOLTAGE (VDC)
LOAD RESIST
ANCE (OHMS)
OPERATING
REGION
Figure 2.14—4-20 mA rate output wiring