Aalborg DPC, Operating Manual

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11
HOST PC
RS-232
RS-485
Up to 64 devices on
one RS-485 segment
Up to 2000 feet
RS-232 to RS-485
Converter
WITH RS-232
INTERFACE
NOTE: RS-232 to RS-485 Converter
has to be configured for 2 wire
half duplex system
ADDRESS: 11 ADDRESS: 12 ADDRESS: 13 ADDRESS: 14 ADDRESS: FF
RS-232
Signal GND
RS-232 TX
RS-232 RX
GND
3 2
1
J4
PHONEJACK
STEREO
1 2
3
J4
PHONEJACK
STEREO
3
2 1
J4
PHONEJACK
STEREO
1 2 3
J4
PHONEJACK
STEREO
1 2 3
J4
PHONEJACK
STEREO
RED
WHITE SHIELD
-SLEEVE GND
-TIP RX(-)
AALBORG P/N: CBL-A485
RX(-)TX(+)GND
T(-)
T(+)
DPC#1
DPC#2
DPC#3 DPC#4 DPC#64
RING TX(+)
TX (+)
RX
(-)
RX
(-)
TX (+)
TX (+)
RX
(-)
TX (+)
RX
(-)
TX (+)
RX
(-)
FIGURE 5: DPC Mass Flow Controllers RS-485 Communication Interface Connections
When the DPC device is set as the last device on the long RS-485 bus segment, the 120

bus termination resistor must be connected between the RS-485 (+) and (-) terminals
close (< 6 feet) to this device.
CAUTION: The DPC instrument offers an integrated switchable 120

termination resistor between the RS-485 (+) and (-) pins. On instruments
with a local display and joystick interface, the 120

termination resistor
can be activated (enabled) using General Settings / Communication Port /
RS-485 Termination menu selection. By default, the instrument is shipped
from the factory with the RS-485 Termination mode set to Disabled.

4. PRINCIPLE OF OPERATION
The DPC fl ow controllers are based on the measurement of the differential pressure across
specially designed restrictor fl ow elements. The restrictor fl ow element is designed to es-
tablish laminar fl ow across the entire range of the instrument’s operation from 0 to 133%
of full scale range. A high accuracy and high resolution differential pressure sensor is uti-
lized to measure pressure drop across laminar fl ow channel, which is linearly proportional
to volumetric fl ow rate. To convert volumetric fl ow in to the mass fl ow, high accuracy and
high resolution absolute pressure and temperature sensors are utilized.
Based on data from the sensors and Gas Properties from the built-in data base of the instru-
ment, the micro-controller calculates Volumetric and Mass Flow, which along with Pressure
and Temperature parameters are available on the instrument display or via digital interfaces.
In addition, the Mass Flow reading is accessible via the instrument Analog interface which
can be set by user to 0-5, 0-10 Vdc or 4-20mA mode.
If custom length cable is required, it can be assembled using the connection diagram
shown in
Figure 5: