The range selection of pollution source automatic monitoring equipment must strictly follow national environmental policies and regulations to ensure the authenticity, accuracy, and completeness of monitoring data. The selection should be based on the emission limits of the monitoring points and the actual operating conditions. The core principle is that the upper limit of the range must meet the normal monitoring requirements, avoid distortion of effective data due to "peak", and fully consider the concentration range of pollutants during stable operation of pollution prevention and control facilities, while also taking into account high concentration emissions under abnormal operating conditions as much as possible.

The calibration of the measurement range and the signal output method are directly related to the validity of the data, mainly divided into the following four situations:

（1） Single calibration curve, analog signal output dual range
This is currently a common method. Although the equipment (such as SO ₂ analyzer) is set with dual ranges (such as 0-100/500 mg/m ³), it only uses one calibration curve and outputs an analog current signal of (4-20) mA. The range switching is automatically determined by the device based on the measured values. This method has limited effectiveness in improving the measurement accuracy of low concentration ranges, and there is a risk of data distortion due to range switching or signal "topping". Under regulatory policies that emphasize the direct application of data, its applicability needs to be carefully evaluated.

（2） Dual/multi calibration curve, analog signal output dual/multi range
This method calibrates separately for different range segments, forming independent calibration curves (as shown in Figure 1), and outputs them through analog signals. Its signal output form is the same as the previous one, but due to independent calibration of different range segments, it can ensure high measurement accuracy throughout the entire measurement range (including low range and high range), which is more in line with the requirements for data accuracy.

（3） Single calibration curve, digital signal output
When the device uses digital signals (such as RS485, network transmission) to directly output pollutant concentration values, range switching is only reflected in the internal display or recording of the device. If only a single calibration curve is used, setting dual ranges has little significance in ensuring measurement accuracy and cannot solve the accuracy problem within the full range.

（4） Dual/multi calibration curve, digital signal output
This is a way to achieve measurement quality. The equipment has dual/multi range and corresponding independent calibration curves, and directly outputs concentration values through digital signals. It not only ensures the measurement accuracy of the equipment in various range ranges, but also avoids the errors and "top touch" risks that may be caused by analog signal conversion through digital transmission, representing the current technical direction that meets high standard regulatory requirements.

In summaryIn the context of strengthening the use of online monitoring data for supervision, adoptEquipped with independent multiple calibration curves and combined with digital signal outputThe equipment that can ensure the accuracy and reliability of monitoring data throughout the entire process is the preferred choice for recommendation. The equipment range configuration and calibration method must be based on meeting the requirements of emission standard supervision and data quality.

SINZEN Xinze Instrument