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.

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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)

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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