-
About JIAYU
-
-
-
Resource Center
-
News Center
-
◉ Introduction to Online Monitoring and Comparison
Online monitoring device comparison verification refers to the service of evaluating the performance and verifying the accuracy of data of various online monitoring equipment through third-party testing institutions. Using manual monitoring as a reference method, the monitoring behavior of verifying the accuracy and effectiveness of pollutant automatic monitoring equipment monitoring results ensures that the monitoring device can provide reliable and accurate data in actual operation, meeting regulatory requirements in environmental protection, industrial safety, quality control and other fields. Through regular comparison and verification, various monitoring data and comparison errors can be obtained in a timely and accurate manner, comprehensively and objectively grasping the operation status of online monitoring equipment, preparing for effective data analysis and overall acceptance of online monitoring systems, and avoiding compliance risks or production accidents caused by data distortion.
The testing content covers the basic performance of the device, data collection capability, communication stability, and consistency with standard methods to ensure compliance with national or industry standards.
◉ Online monitoring and comparison of legal basis and requirements
According to the Regulations on the Administration of Pollutant Discharge Permits, polluting units are required to conduct self-monitoring in accordance with the law and keep original monitoring records. At the same time, documents such as the General Principles of Technical Guidelines for Self Monitoring of Pollutant Discharge Units provide specific technical guidance.
Polluting units should develop detailed self-monitoring plans, clarify monitoring points, indicators, frequency, and methods, and ensure the authenticity and accuracy of monitoring data. For online monitoring systems, regular comparative monitoring is required to verify their accuracy and reliability.
◉ Specific implementation of comparative monitoring
（1） Compare monitoring content and projects
Comparative monitoring usually involves comparing online monitoring equipment with manual monitoring methods to evaluate the measurement accuracy and stability of online equipment. The monitoring items should cover the main pollutants of the polluting units, such as sulfur dioxide and nitrogen oxides in the exhaust gas, chemical oxygen demand and ammonia nitrogen in the wastewater, etc.
Zero drift, range drift, indication error, repeatability, response time, linear error, temperature influence, humidity influence, voltage fluctuation influence, signal transmission stability, data acquisition integrity, communication protocol compliance, anti-interference ability, calibration function verification, alarm function testing, data storage ability, clock synchronization accuracy, airtightness detection, insulation resistance, protection level verification, etc.
（2） Compare monitoring scope
Smoke online monitoring system, water quality online monitor, atmospheric environment monitoring station, VOCs online monitoring equipment, noise online monitoring system, radiation environment monitor, sewage discharge monitoring device, heavy metal online analyzer, gas leakage monitoring system, dust concentration monitor, temperature and humidity online monitoring equipment, pH online monitor, dissolved oxygen online monitor, flow online monitoring device, pressure online monitoring system, wind speed and direction monitor, vibration online monitoring equipment, toxic and harmful gas monitor, water quality five parameter monitor, odor online monitoring system, etc.
（3） Compare monitoring frequency
The frequency of comparative monitoring should be determined based on the actual situation of the polluting unit and regulatory requirements. Generally speaking, for key polluting units or enterprises with unstable emissions, the frequency of comparative monitoring should be increased to ensure the accuracy of online monitoring data.
（4） Compare monitoring methods
Comparative monitoring should adopt national or local standard monitoring and analysis methods to ensure the comparability and accuracy of monitoring data. At the same time, the detailed process and data of comparative monitoring should be recorded for inspection.
Standard gas comparison method: using standard gases to verify the accuracy of gas analyzers
Weight method: Verify the accuracy of particle monitoring data through weighing
Chemical analysis method: comparing laboratory chemical analysis methods with online data
Spectral analysis method: using spectral technology to verify the reliability of monitoring data
Electrochemical method: Verify sensor performance through electrochemical principles
Dynamic gas distribution method: used for linear testing of gas analyzers
Multi point calibration method: full range calibration verification of monitoring equipment
Interference testing method: evaluating the impact of cross interference on monitoring results
Environmental adaptability testing: Verify the stability of the device under different environmental conditions
Long term stability testing: evaluating the performance changes of equipment during continuous operation
Communication protocol testing: verifying the compliance of data transmission protocols
Sampling system testing: Evaluating the representativeness and accuracy of the sampling system
Data integrity testing: checking the integrity of data collection and storage
Alarm function test: Verify the reliability of the device's alarm function
Safety performance testing: Evaluating the electrical safety and explosion-proof performance of equipment
（5） Monitoring data management and disclosure
Data recording and preservation: Polluting units should establish a comprehensive monitoring record ledger, recording information such as the time, location, indicators, methods, and results of comparative monitoring. The original monitoring records and monitoring reports should be kept for at least 5 years for inspection purposes.
Information Disclosure: Polluting units should disclose comparative monitoring information to the public through enterprise websites, information platforms designated by environmental protection departments, and other channels in accordance with regulations and deadlines, and accept social supervision.
◉ Common problems
（1） Who should be considered as the standard when laboratory data is significantly lower than online monitoring data?
Online comparison is based on laboratory monitoring data. When there is a significant difference between online monitoring data and laboratory data, the laboratory can further conduct error analysis to verify the sources of errors such as systems, methods, environments, reagents, etc. The technical specifications for continuous monitoring of fixed pollution source flue gas emissions (SO2, NOX, particulate matter) (HJ75-2017) and the operational technical specifications for online monitoring systems for water pollution sources (CODCr, NH3-N, etc.) (HJ355-2019) both describe the use of laboratory monitoring data as a benchmark to determine the accuracy of online monitoring.
（2） What parameters may affect the accuracy of the comparison?
Exhaust gas: cross-sectional area, measuring range, pitot tube coefficient, velocity field coefficient, regression curve/K coefficient of particulate matter, etc.
Wastewater: measurement range, calibration factor, correction value, digestion time, digestion temperature, etc.
（3） What aspects should be noted before comparison?
1. Exhaust gas:
The temperature of the heat tracing tube is above 120 ℃, and the temperature of the condenser is 2-6 ℃. Malfunctions can cause condensation and blockage in the gas path, and the value cannot be measured.
During the sampling process, the blowback function must be turned off. The reverse blowing path will cause the flow velocity to become zero, resulting in a zero value for the extracted pollutants.
Pay attention to the marking position, compare the exhaust gas flow rate, mark it as position N, otherwise it is invalid data.
2. Wastewater:
The pH and online pH probes should be compared at the same sampling point.
According to the requirements of 354 and 355, it is necessary to sample through the mixing port of the automatic sampler. When comparing, the sample is usually taken immediately after the automatic sampler supplies the sample, and the sampling time is the display time of the analyzer data.
Pay attention to the marking position. When making quality control samples, substitute samples, or accuracy samples, generally cut the C mark. The actual water sample comparison should have drainage and flow rate, and the marking position should be N, otherwise it is invalid data.
Please record the data time on the data acquisition instrument. If the instrument and data acquisition instrument use 4-20mA signals, there may be errors. The data uploaded to the platform by the data acquisition instrument shall prevail.
（4） With the implementation of HJ1331 and HJ1332 portable methods for non methane total hydrocarbons, what are the advantages and disadvantages compared to HJ38 before?
Portable instruments can read directly on site, which is closer to the status of online monitoring equipment and also closer to the data. However, the detection accuracy of portable instruments is not as high as that of laboratory gas chromatographs (high detection limit), and portable instruments use hot and wet methods for testing, requiring additional humidity testing to convert their test values to dry basis values, which requires higher requirements for on-site sampling personnel.
（5） What are the possible situations where the particle reference method has high data but low online monitoring data?
1. The regression curve or K coefficient calculation for online monitoring may be incorrect;
2. When debugging, there is no condition for using regression curves, and the K coefficient method should be used;
3. The particulate matter is extracted without using constant velocity sampling method, or the tracking rate does not meet the requirements;
4. The discharge process is relatively special, for example, pollutants produce extremely fine particulate metal salts during the treatment process, which increases the weight of the filter membrane.
◉ Compliance Services
As a professional third-party testing technology service organization, Jiayu Testing has qualifications such as CMA and CNAS. In the field of environmental testing, it currently has more than 1000 CMA testing parameters, covering water and wastewater, air and waste gas, soil and sediment, noise and vibration, and solid waste toxicity identification. The laboratory is built and managed strictly in accordance with standards, equipped with advanced instruments and equipment, and has a professional technical team with superb skills. It has rich industry service experience and strong testing technology capabilities. Based on the principles of objectivity and fairness, it provides authoritative testing reports with legal effect to the society, and provides full chain environmental risk management support for enterprises and regulatory departments. Welcome to contact us, Jiayu Testing Consultation Hotline: 400-9269-886!
Recommended for you
Wechat Public
Account
Hotline
Hotline
Follow
The Public
Follow Us
- Back