VEGA D91 Profibus PA - Manual (Page 4)

4 Pressure transmitter D91 (Profibus PA)
Product description
1 Product description
1.1 Function and configuration
D91 pressure transmitters, which incorporate
an isolating system, are efficient instruments
for hydrostatic level measurement. The hy-
drostatic pressure of the medium acts on the
separating diaphragm of the isolating system
and is transferred via the isolating liquid to a
ceramic-capacitive CERTEC
® measuring cell.
The pressure on this measuring cell effects a
capacitance change within the measuring cell
via the diaphragm. This capacitance change
is detected by an ASIC (Application Specific
Integrated Circuit) and converted into a pres-
sure-proportional signal by the integrated
electronic module with microcontroller. Pre-
cise, high-resolution digital processing of
measurement data ensures excellent techni-
cal data.
Isolating systems are used to protect the
measuring cell against aggressive products
or high temperatures. By selecting the suit-
able isolating liquid and diaphragm material,
systems with a temperature resistance up to
400°C are possible.
The electronics module is powered by a
Profibus DP - PA segment coupler. The
measured pressure is transmitted as a digital
signal via the bus cable to the processing
system and can be displayed on the indicat-
ing module.
To improve reliability, the functionality of im-
portant electronic components is continu-
ously checked, and internal parameters such
as sensor value, temperature and operating
voltage are closely monitored.
The pressure transmitters with ceramic
CERTEC
® measuring cell offer the advantage
of continuous self-monitoring: measuring and
reference capacitances of the measuring cell
constitute a predefined ratio over the entire
measuring range. Any deviation from these
data is a reliable indicator of a malfunction of
the measuring cell. If errors or malfunctions
are detected during these routines, fault
signals are triggered according to the
Profibus PA specification.
The pressure transmitter D91 consists of two
parts, the transmitter and the processing
unit. Both parts are connected via a three-
wire screened cable (depending on the ver-
sion, with or without breather capillaries). The
processing unit contains the adjustment
elements (address switch, keys and LCD)
and the terminals for the Profibus PA cable.
0 - 20 bar
Transmitter
Processing unit
Profibus PA
cable