Implementation of a PC-based data-logger software for air pollution monitoring networks

Transcription

1 Air Pollution XIII 455 Implementation of a PC-based data-logger software for air pollution monitoring networks G. Latini 1, L. Magnaterra 1, S. Tascini 1 & G. Cencioni 2 1 Dipartimento di Energetica Università Politecnica delle Marche, Ancona, Italy 2 Ecos s.a.s., Ancona, Italy Abstract Automatic acquisition of meteorological and air pollution data is a central aspect in environmental monitoring. A monitoring network is composed of a set of stations with complex acquiring devices, a data-logger and a communication system. All the components of the network can be a source of failures. The stations are usually located far from laboratories and are intrinsically prone to malfunctions. This paper describes the most relevant aspects of a new datalogger software, developed by the authors in collaboration with the company in charge of installation and maintenance of the environmental monitoring network of Ancona Province, Italy. The aim of the project was the development of a costeffective system which is easy to use, maintain and configure, which shall be able to prevent data loss for long time periods. The system is PC-based with the capability of remote configuration and especially remote calibration of acquiring devices. 1 Introduction Environmental monitoring networks are composed of stations with complex, and often very expensive, acquiring devices but the basic role is played by the datalogger that continuously stores data from all devices in the station and sends them, on demand, to the master control centre. Obviously, data-logger breakdowns and/or malfunctions are a primary cause of data loss, also for long time periods if the problem is not quickly detected and fixed [1]. In the environmental monitoring network of Ancona Province, data-logger malfunctions represent the main cause of data-loss, therefore the company in

2 456 Air Pollution XIII charge of installation and maintenance of the network, the ECOS s.a.s., in collaboration with the authors decided to develop a software for a new PC-based data-logger that shall overcome many of the problems leading to data loss. The PC-based system is a cost-effective solution and presents many advantages with regard to an ordinary data-logger: - it is easy to maintain since broken parts can be quickly detected and substituted with a variety of marketed hardware; - it is easy to configure and each station can be equipped with somehow different hardware, according to the kind of acquiring devices into the station itself; - it is characterized by great possibilities of upgrade and expansion. 2 Hardware and software architecture The data-logger core is a set of data acquisition boards for the PCI-bus, installed into a Personal Computer. The prototype supports up to six PCI cards, but the required number of PCI-slots depends on the number of analog or digital inputs and on the kind of acquisition cards. Furthermore, to make the remote control of devices feasible, the PC must have a suitable number of serial ports. The system has been tested with two Advantech PCI-bus cards, namely a 100 KS/s, 12-bit resolution, 32-channels Isolated Analog Input Card [3] and a 48-bit Digital Input/Output Card [4]. With this composition the logger can have up to 32 differential or 16 single-ended analog input channels or a combination. Besides hardware malfunctions, data losses also originate from wrong configurations that lead to non-valid sampled data. Therefore the aim of the project was also the development of automatic acquisition and configuration software with a clear and straightforward interface to prevent human errors. The software has been developed through Visual Basic for Microsoft Windows 2000 Operating System and is composed by a Client Software and a Server Software. The Server Software, installed on the data-logger of the remote station, consists of four processes (Figure 1): - Father Process (FP) - Acquiring Process (AP) - Logging Process (LP) - Communication Process (CP) At the system start-up, the Father Process configures the whole system according to the configuration database, and then starts the AP and LP processes (son processes). The Acquiring Process handles the communication with the PCI-cards; it continuously reads values from analog and digital channels and stores them into PC reserved memory locations. The Logging Process handles the update of database records containing the sampled data. LP converts values read by the AP from volts to proper units, and saves them according to the userdefined sampling rate; moreover it computes and stores hourly means. The Communication Process handles the connections with a remote client that by means of the Client Software can download and modify the current configuration, upload a new configuration and manage acquiring devices connected to PC serial ports.

3 Air Pollution XIII 457 Figure 1: The Server Software structure. To enable the server-client link, the user must only define a standard RAS connection within the server PC. No other action is required as the PC operating system manages communication and file transfer. 3 System configuration and control The operator can interact with the data-logger by a simple GUI. The start-up form (Figure 2) is divided in two main sections; a configuration section (CS) with buttons that point to forms used to modify the configuration database, and a visualization section (VS) with buttons that lead to forms used for monitoring the data-logger activities. Figure 2: The Server Software start-up form. By the VS forms the operator can observe values acquired by the PCI cards, in voltage and in converted units, can examine data collected during the last 24 hours and can check the status of the link with the control station [2]. The Measures Control Form (Figure 3) shows pollution and meteorological data acquired by the Logging Process both in PPB and physical units. In

4 458 Air Pollution XIII addition, by this form is possible to enable or to disable a measurement process, just clicking on the related led on the right. Figure 3: Measures control form. When a measurement is disabled, for instance because the operator performs an instrument calibration, a flag into the database will point out that the sampled value must be rejected. Likewise to the Measures Form, the Digitals Control Form shows the status of digital alarms. 3.1 The configuration database Information regarding data-logger set-up is stored in the configuration database that contains tables regarding the following elements: - station identification (such as name and ID number) - identification of PCI-boards (type, features and PCI slot) - set-up of all channels (input/output, single-ended/differential) - set-up of measurements - set-up of digital alarms Every change of the system current configuration forces FP to read again the database and to restart the son processes AP and LP. When FP starts, it checks the installed PCI acquisition cards and the station ID. If the station or one of the found cards is not properly configured into the database, the acquisition is stopped and a warning is generated. The configuration tables for the cards can be modified through the PCI Card Configuration Form (Figure 4). Such tables are important since most boards do not maintain the channel set-up when the PC is turned off. Practically, FP reconfigures the PCI boards whenever the PC is switched on, according to the previous set-up data stored into the database.

5 Air Pollution XIII 459 Figure 4: PCI cards configuration form. Figure 5: Measurement configuration form.

6 460 Air Pollution XIII Figure 5 shows the Measurement Configuration Form, by which the user defines all the measurement that shall be logged. The software automatically generates the ID number of the measurement device while the operator should set the following parameters: - name - units - sampling rate - type of mean (arithmetic or vectorial) - acquisition board - channel s ID number on the board - type of channel (differential or single-ended) - input voltage - output voltage of the analyser - type of measure (analog/digital, voltage/current) - conversion coefficients from volts - filtering options Filtering options have been introduced to implement an automatic data prevalidation. The data-logger can reject a value that differs from the previous one by a specified quantity in module or in percentage. After the operator has opted for choice values, the program checks if a channel has been assigned to more than one analyser then, for each new parameter, automatically generates the variables to store the hourly means and the digital status of the measures. 4 Remote control Figure 6: The Client Software GUI. The master control centre, through the Client Software (Figure 6), can make a remote set-up of the data-logger, and a remote calibration of some acquiring

7 Air Pollution XIII 461 devices, establishing a communication by any analog, ISDN or GSM modem. Moreover the Client Software is able to perform the data download from the remote measurement stations. If enabled, data download can be executed manually or automatically, by choosing a calling time. From a local database the Client Software reads the connection parameters for the remote stations, for example name, phone number, passwords and can download data from all the stations using a user-defined calling sequence. The automatic download feature can be utilized only when the Server Software is installed in all the stations of the network. Therefore it had to be disabled during the test sessions, since Ancona Province still makes use of another software to automatically download data. 4.1 Data-logger remote configuration Remote Configuration is based on the exchange of the configuration databases between control centre and remote stations. A simple communication protocol has been implemented to transfer the configuration databases. When the Client Software, running on the control centre PC, requests the configuration database, the Server Software in the measurement station places a copy of its database in a shared folder and sends a message conf request ok. The copy is then transferred via FTP. The user modifies the database and then retransfers it. When the transfer is complete the acquisition process in the remote data-logger is restarted. The Client Software, continuously checks to avoid changes into the configuration database that could lead to ambiguous or wrong situations. Only the Server Software in the remote station can make a number of operations; for example, the operator in the control centre cannot add a new element to the list of existing acquiring devices or assign a new channel s ID number to an acquiring device. Some allowed actions are: - to rename measures - to adjust the conversion parameters - to modify the sampling rate - to change the filtering options - to disable or enable measures 4.2 Device remote control and calibration Most acquiring devices can be remotely controlled by a host RS-232 device such as PC. Since the communication protocol is different between devices, it was necessary to write a DLL for each model. With the Device Remote Control and Calibration Form (Figure 7) the user can select the analyser to control and send a command selectable among them recognized by such device. Furthermore the user can send a complete sequence of commands to perform a defined operation. To test the remote control, we connected two devices to the data-logger, namely a chemi-luminescent Nitrogen oxides analyser [5] and a UV photometric Ozone analyser [6]. Both analysers have been controlled via RS-232 from the Client Software, without any particular problem. While sending RS-232

8 462 Air Pollution XIII commands to examine or change analyser set-up is quite easy, remote calibration procedure may be more complex. In general, analysers should be re-calibrated with a certain frequency, usually multipoint calibration is recommended in the following conditions: - no later than three months after the most recent calibration or performance audit which indicated analyser calibration to be satisfactory; - interruption of more than three days in analyser operation; - any time major disassembly of components; - transfer of the analyser to another location - any time the zero or span drifts exceed the calibration limits Figure 7: Device remote control and calibration form. Remote calibration is one of the main goals that this project attempted to achieve. By RS-232 commands it is possible to simulate pressing the analyser front panel pushbuttons; therefore the remote operator can remotely control the calibration sequence following the same procedure to be performed into the station, in front of the analyser. The major difficulty is that several analysers require an external gas source to be calibrated. To drive the gas flow, the system uses a regulator controlled by one of the output channels of a PCI-board (Figure 8). 5 Conclusions For a test the new data-logger has been installed into an existing measurement station, which collects the following data: o Concentration of Nitrogen oxides (NO, NO 2, NO x )

9 Air Pollution XIII 463 o Concentration of Sulphur dioxides (SO 2 ) o Concentration of Carbon monoxide (CO) o Concentration of Methane (CH 4 ) o Concentration of hydrocarbons (HC) o Concentration of non-mechanic hydrocarbons (NMHC) o Concentration of dust particles (PM10) o Sun radiation o Air temperature o Wind direction o Wind speed Figure 8: Remote calibration implementation. During test sessions both software and hardware worked fine. We encountered difficulties during the integration of the first test station equipped with the new data-logger within the existing network. Ancona Province airquality database has an obsolete structure, really inadequate to manage a large number of measurement stations. For instance the ID numbers of measures are manually assigned and moreover all the measures into the whole database are identified by a single progressive integer number, while ECOS data-logger performs an automatic assignment and identifies a measure by two numbers: the measure ID and the station ID. This approach makes simpler to add or to remove acquiring devices into a station or the station itself into the network. In order to make the new database compatible with the existing one, we had to write conversion software, but a complete reorganization of Ancona Province air-quality database is strongly recommended. Tests are still in progress. However after preliminary results we can declare that the PC-based data-logger really seems to be working fine. It is a cost-

10 464 Air Pollution XIII effective solution, and the possibility to remotely control the analysers makes the system very important in the management of a wide monitoring network. References [1] Latini G, Passerini G, Handling Missing Data: Application to Environmental Analysis, WIT Press [2] Magnaterra L, Tascini S, ECOSoft 1.0 User s Guide, [3] PCI channel Isolated Analog Input Card User s manual, Advantech Co., Ltd., [4] PCI bit Digital Input/Output Card for PCI Bus User s manual, Advantech Co., Ltd., [5] Model 200A Nitrogen Oxides Analyzer Instruction Manual, Advanced Pollution Instrumentation, Inc., [6] Model 49C UV Photometric O3 Analyzer Instruction Manual, Thermo Environmental Instruments, Inc., 2000.