Remote monitoring of parameters for a pressure transducer through hart protocol and LabView environment.
Rancea, Irina ; Sgarciu, Valentin ; Stamatescu, Grigore 等
1. INTRODUCTION
Technological process supervision involves acquisition and
monitoring of a large number or parameters. Using the Internet
connection one can store those parameters in high performance servers
and data bases. The paper is focused on a solution for monitoring
parameters for a pressure transducer with sensitive piezorezistive
element through the HART protocol, designed for long distances.
2. SYSTEM ARCHITECTURE
2.1 Hardware Resources
The system uses the relative pressure transducer SITANS P, MS
series, 7MF4013 manufactured by Siemens. Its schema is presented in
Fig.1. The transducer measures the relative pressure (the difference
between process pressure and atmospheric pressure); this pressure is
then converted in unified electric signal, scale 4/20 mA cc. The
transformations flow is: pressure difference [right arrow] force [right
arrow] modification of electric resistivity [right arrow] electric
current. The pressure [p.sub.e] is passed through process connector to
the measure cell. The pressure is sent to a silicone piezorezistive
sensor through the diaphragm and the filling liquid that takes over the
distorsions of the measure diaphragm. As a result of pressure variations
the resistance of the four sensistive pizorezistive elements connected
in a bridge is changed. This generates an output tension from the bridge
balanced with the input pressure. The tension is amplified by the
measure amplifier and converted in digital signal that is evaluated by
the microcontroller and then converted through the Digital-Analog
convertor. The analog output has a variation between 4mA and 20 mA for a
pressure variation between [p.sub.min] and [p.sub.max]. The transducer
can be set to a conditional point of working through the two buttons or
through the HART modem.
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2.2 HART Communication Protocol
The HART communication is realized between two devices: a field
device and a control or monitoring system. HART provides two
simultaneous communication channels: analog signal 4-20mA and digital
signal. The 4-20mA signal communicates the primary measured value using
a current loop of 4-20mA--it is one of the fastest and reliable
industrial standards. (Merget, 2003)
HART is a master-slave communication protocol every slave
communication (field device) is initiated a communication master device.
On every HART loop two masters can be connected. The primary master is,
in general, a distributed control system (DCS), programmable logic
controller (PLC) or another PC. The slave devices can be transducers,
executive elements and control equipments. (Lu et. al, 2007) (Fig. 2)
The HART communication protocol is based on the Bell 202 communication
standard and operates using the FSK principle. (Pereira et. al, 2003)
The devices that can communicate through the HART protocol can work in
two network configurations: point-to-point and multipoint.
[FIGURE 3 OMITTED]
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HART Server is a specialized software that allows building
hierarchically extended configurations and facilitates the data access
from HART devices and associated processes in a format that can be used
in different management applications. (Fig. 4) (Wang et. al, 2007)
2.2 Application Architecture
The monitoring system is installed and configured on a local
workspace; the access to the application server is done through an
Internet connection, as in Fig. 5., Fig. 6. and Fig. 10. (Vlad et. al,
2005)
The application has a communication module that is responsible with
the remote data transmission. It was developed using NI DataSocket
Server-Client communication. The server module writes data in the
server, and every client can read/write data due to his rights. Also,
the server application can read command data from the server and apply
it to the sensors (Fig.4 and Fig. 5).
3. CASE STUDY
The assembly contains the following modules (Fig. 9):
--Compressor--power supply with compressed air able to maintain o
pressure of 8 bars. When the pressure is under 6 bars it starts
automatically.
--RP--pressure reducer
--ME--Manometer--pressure analog indicator of high precision, HEISE
manufactured, class 0.1, domain 0-4 bars
--Basin--container that simulates a tehnological installation
working with pressure till 10 bars
--TP--SITRANS P DM--pressure transducer, configurable through HART
protocol
--RE--evacuation faucet and simulate disturbances
--SA--power supply of 24 V cc
--SV--servo-valve 8288200.9650.02400
--DI-158U--acquisition/distribution of numerical and analog data
module connected to PC through USB (DATAQ manufactured)
[FIGURE 6 OMITTED]
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[FIGURE 9 OMITTED]
[FIGURE 10 OMITTED]
The operating mode of the transducer through HART protocol can be
configured wit the HART Server application (Fig. 7 and Fig. 8). OPC (OLE
for Process Control) has a communication interface between various
sources of data and applications that provides the information from
those sources. The main target of the OPC Server is to transfer data
through unshared routes of communication to physical devices. HART
Server can obtain information from the configured HART devices such as
their state, their configuration parameters and their tolerance.
4. CONCLUSIONS
The application was designed and developed to test the possibility
of adding remote monitoring. It was used for a series of experiments
between several laboratories. As main part of this paper we presented
the process of remote monitoring of the pressure transducer with
sensitive piezorezistive element, but the server can deal with more than
one application in the same time. In the future we will implement it in
an industrial factory.
5. REFERENCES
Lu X.; Guo W. (2007). The Application of HART protocol in the
Converter of Magnetic Flowmeter, Proceedings of the World Academy of
Science, Engineering and Tehnology, Vol. 23, august 2007, ISSN 1307-6884
Merget O. (2003). The Electronic Integration of Field Devices, IEEE Computing & Control Engineering Journal, Vol. 14, october-november
2003, pp. 22-23
Pereira J.; Postolache O.; Girao P.S. (2003). HART Protocol
Analyser based in LabView, Intelligent Data Acquisition and Advanced
Computing Systems: Technology and Applications, proceedings of the
second IEEE International Workshop, september 2003, pp. 174-176
Vlad, M.; Sgarciu, V.; Rancea, I. (2005). Acquisition and
monitoring of process parameters using Internet, CSCS15--15th
International Conference on Control Systems and Computer Science,
Politehnica University Bucharest, Vol. 1, pp. 8-14
Wang H.; Shi L.; Yank X.; Xu S. (2007). Research and Development of
On-line Monitoring and Management System to Hart Field Devices, IEEE
Electronic Measurement and Instrument, ICEMI, 8th International
Conference, pp. 3-410-3-402