Air Monitoring 39
a resolution of 32-bit fl oating number according to IEEE 754. All communication interfaces must be well documented. The data sampling rate shall be at least every 10 seconds and manual data input is allowed for certain parameters.
C Input processing and production of FLD Loss of connection to the interfaces must be identifi ed. Input data is valid if the connection is valid and the AMS is in measuring mode. FLD shall be stored along with status information and, if the raw concentration is scaled, any scaling factors that have been applied.
D Calculation of reported data Figure 2: Importance of data averaging rules
Long-term averages (LTA), including daily averages, are calculated by averaging the validated STA data. The qualifying period for daily averages is 6 hours, i.e., the daily average is reported only when there are at least 6 h of valid STA data. Other long-term averages have a qualifying period of at least 10% of the LTA period, e.g., at least 72 hours or three days for a monthly average.
Mass emissions are calculated by multiplying the unvalidated concentration data by the stack fl ow data in the usual way, noting that these must be at the same reference conditions. However, the mass emission is set to zero if there are negative STA values of either concentration or fl ow.
Other topics covered by Part 1 of the standard include: i) defi nition of report contents; ii) monitoring and reporting the number of AMS invalid days, e.g., days with three or more missing STA for Large Combustion Plant; iii) fl ow weighted averaging for common stacks; iv) calculation of rolling averages; v) calculation of percentile concentrations; vi) monitoring and reporting exceedances of the Valid Calibration Range and vii) manual data entry.
EN 17255 Part 2 – DAHS requirements
Part 2 of the standard specifi es requirements for data acquisition, data processing, data storage, data output, the generation of reports, system functions and data integrity.
A DAHS The various elements of the DAHS, including interfaces with the AMS, are shown in Figure 3 with the functionality described earlier mapped onto these elements in Figure 4.
B Interfaces Analog communication resolution shall be at least 12-bit (recommended 16-bit) with a relative accuracy better than 0.1% of range. Digital communication transfers the associated status information to the DAHS ensuring that there is unique addressing of input data sources, and synchronised transfer of values, and their corresponding status signals, with
Calculation of the calibrated, standardised and validated short- term averages follows the procedures specifi ed in Part 1 of the standard as described above and as illustrated in Figure 4 which also shows the calculation of long-term averages and comparisons with the appropriate ELVs. Part 1 states that the QAL2 calibration is applied to the short-term average and notes that the QAL2 calibration can be applied to the fi rst-level data without changing the results, as implemented in Figure 4.
Mass emissions calculation and reporting is also shown in Figure 4 with an example of submission of total annual mass emission to the European Pollutant Release and Transfer Register (E-PRTR).
Warnings, Alarms and Violations Monitoring of ELV exceedances (violations) and the AMS operational states, with the generation of corresponding alarms, is mandatory. An alarm shall be raised if the connection to an input source is broken. Alarms shall be stored with a start and an end timestamp, or with a start timestamp and an associated duration. Transmission of signals and alarms to external systems is required, e.g., the plant Distributed Control System (DCS).
E Report generation
System reports These reports shall contain: periods/hours of DAHS unavailability over the calendar year; FLD for selected inputs; QAL2/AST data, e.g., calibration functions and the Valid Calibration Rang along with the dates/times of the QAL2/AST testing and the associated parameter setting within the DAHS; QAL3 drift corrections (if applicable); event log entries; listing of warnings, alarms and violations with dates/times; DAHS confi guration parameters with the date/time of the last revision; version numbers for software modules.
Emissions reporting for compliance purposes varies between Member States and sometimes within Member States. The DAHS must obviously be capable of producing these bespoke reports in the required formats and media, e.g., as a pdf or as an Excel workbook.
F Data storage The following requirements are specifi ed for the data storage system: multiple concurrent user access; encrypted communication; tamper-proof data transfer and handling; permanent data retention for at least fi ve calendar years; backup on an external device and prevention of data loss by transaction secure write operations.
System functions A watchdog is required to ensure that all elements of the DAHS are working as expected with an event log to record any unexpected or signifi cant events, e.g.,
Figure 3: DAHS elements
confi guration changes. It must be possible to set the DAHS in a test mode to verify the confi guration and check the reported data. The results shall be exportable in a simple, machine-readable format. With regards to system time management, a built-in motherboard PC clock is not suffi cient and the use of a server with Network Time Protocol capability is allowed.
The event log shall include the: type of event (e.g. unsuccessful attempts to log in, communication faults to AMS, power cuts, watchdog restarts, changes to the system clock more than 5 seconds); event description; event category, e.g., an important event requiring immediate action or a less important event with an advisory notifi cation; user name associated with the event and the time stamp of the log entry. Examples include: confi guration changes; power loss; data communication issues and a change of the time clock greater than 5 seconds.
Part 2 of the standard covers only the basic structure of a DAHS, although the exact defi nition of where a DAHS starts and ends is useful guidance for the DAHS supplier. The requirements emphasise that secure data transmission is a must have in a modern IT environment. However, it should be noted that the detailed emissions reporting requirements are defi ned by local standards and guidance within each Member State.
EN 17255 Part 3 – DAHS Performance
testing (certifi cation) Part 3 of the standard requires certifi cation (type approval) of the DAHS and specifi es how the requirements of Parts 1 and 2 of the standard are checked and verifi ed during certifi cation. This allows the plant operator to install a pre-qualifi ed DAHS at the plant.
System tests are conducted by an independent test laboratory, on a single DAHS unit, with subsequent type approval granted by an independent certifi cation body, e.g., TÜV. Every component of the DAHS is tested, i.e., all of the elements shown schematically in Figure 5.
Part 3 specifi es and describes the DAHS test procedures and defi nes what is required of the independent test laboratory. Tests are defi ned as generic, specifi c (requiring additional test equipment and procedures) and documentation based, and the test results are assessed against the performance criteria defi ned in Parts 1 and 2 of the standard. Specifi c tests often require the injection of a test signal into the DAHS. Reporting checks take into account the intended application, e.g., Large Combustion Plant or Waste Incineration plant, and the system documentation is also reviewed.
Figure 5: DAHS architecture Procedures are defi ned for checking the following elements:
• Data acquisition: emissions, peripheral, fl ow, plant and manually entered data; sampling rate/resolution; Analogue Digital input ranges and accuracy; live zeros (a non-zero voltage or current is assigned to the start of the measuring range, enabling monitoring for broken wires) and the remote data logging unit.
• Input data processing: FLD formation, including the sampling interval; data fl agging as valid/ invalid/out-of-range and QAL3 drift corrections (if applicable).
• Reported data: implementation of the calculation procedures for FLD, STA and LTA and checking warnings, alarms and violations.
• Reports: Generic and regulator specifi c emissions reports; system reports and the functioning of automatic and/or manual report generation.
• Data storage: date/time stamping; FLD, STA, warnings, alarms violations and events.
• System functions: check that every action shows up in the Event Log (DAHS initiated or manually entered); check that all confi guration modifi cations are recorded in the Event Log; test
Figure 4: Data handling processes
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