CEMS particulate matter monitor

3. Schematic diagram of host structure

●The host includes a laser light source and power control unit, a photoelectric sensing and small signal preprocessing unit, a scattered light receiving unit, a display and input unit, an output driving unit, and a main control unit. The 650nm beam emitted by the laser enters the emission source at a small angle, and the laser beam interacts with smoke particles to produce scattered light. The backscattered light enters the sensor through the receiving system and is converted into an electrical signal for processing The circuit part realizes the functions of photoelectric conversion, modulation of laser beam, signal amplification, demodulation, power control of light source, and V/I conversion.

System Schematic Diagram

2. Selection of parameters

●The measurement range and measurement area of the HRD-SK-3001 particulate matter monitor are adjustable under on-site conditions, but the adjustment process is relatively complex. It is recommended that users select accurate parameters for the manufacturer to adjust when ordering to simplify the installation process. Generally, when the user does not specify the parameters, the measurement range of the manufacturer's factory is adjusted to (0-200) mg/m3, and the DGT parameter of the measurement area is adjusted to 2000mm. The better working state of general measuring instruments is around 2/3 of their full range, but it is not the same for smoke detectors, whose working point is at 1/3 or even lower of their full range. This is because the on-site smoke and dust emissions have a large dynamic range even when the dust removal equipment is working normally. The electrostatic precipitator with three electric fields often operates in the state of three electric fields, two electric fields, or even a single electric field. The bag filter also often operates in situations where one or several bags have slight leaks. Therefore, the smoke detector needs to balance the accuracy of measurement and a large dynamic range.
●The measurement area of HRD-SK-3001 particulate matter monitor refers to the length of the area in front of the smoke and dust monitor where the backscattered light generated by the interaction between the laser beam of the smoke and dust monitor and the particulate matter can be perceived by the receiving system if there is particulate matter. For the HRD-SK-3001 particulate matter monitor, the backscattered light generated by the interaction between particles and laser beams within a distance of 2500mm in front of the smoke and dust monitor can be perceived by the receiving system, while particles beyond 2500mm cannot be received by the receiving system even if they have scattered light. The measurement area of the smoke and dust monitor is marked on the instrument nameplate. There are two key points for its use: one is that the parameter must be greater than or equal to the distance from the flange end face of the smoke and dust monitor to the opposite chimney or flue wall, ensuring that the reflected light from the flue wall does not mix with the scattered light of the smoke and dust monitor; In addition, this parameter must be greater than the thickness of the flue wall plus a distance of about 300-500mm to ensure that the measurement area is inside the flue.

3. Installation

The situation where the pressure at the measuring point is negative pressure

The situation where the pressure at the measuring point is positive pressure

3. High concentration issue

Both the optical method and the scattering method have nonlinear problems at higher concentrations, which means that there is no proportional relationship between concentration and instrument output. Both the scintillation method and the electrostatic induction method have similar situations. Fortunately, within the concentration range required for general emission monitoring, the deviation caused by this non-linearity can be ignored. Generally speaking, without precise calculation and on-site experience estimation, optical and electrostatic induction methods do not need to consider the deviation caused by non-linear factors when the smoke concentration is below 500mg/m3 (here, non-linear only refers to non-linear factors caused by light or charge changes due to interference between particles). Of course, for the penetration method and scintillation method, the size of the optical path should also be considered, and for the scattering method, the size and position of the sampling measurement area should be taken into account. In some cases, it is necessary to measure high concentrations of smoke and dust emissions. For example, at some measuring points before desulfurization and dust removal, the smoke and dust concentration may exceed 1000mg/m3, while at some measuring points, the smoke and dust concentration can reach 20g/m3. In this case, nonlinear factors must be considered. In fact, if each set of instruments is installed on site for environmental monitoring, a reference is required to accurately quantify the relationship between instrument output and smoke concentration. Broadly speaking, the correlation and linear relationship between two sets of data are two different concepts. The correlation coefficient between two sets of data is 1 (or completely correlated), but the relationship between them may not be linear. Therefore, there is still an issue of matching patterns between the two sets of data. The relationship matching pattern between the two sets of data (reference data and instrument recorded data) in the reference experiment is generally achieved through multiple regression. Generally, quadratic regression can be used to meet the environmental emission standards. So for measurements at high concentrations, a regression matching pattern with at least two iterations is required. For data regression, first make the regression data into two rows and then follow the following steps to directly perform it using Excel:
1Click on the Chart Wizard
2Select the scatter plot and click 'Next'
3Select the two rows of data to be regressed and click 'Next'
4Click 'Finish'
5Move the cursor to the data point in the figure, click to select the data series, and then right-click
6Select 'Add Trend Line' from the menu discussed
7Select 'Polynomial Regression', choose order 2
8Click on the 'Options' page to check' Display Formula 'and' Display Correlation Coefficient '‘
9Confirm completion

The 4-20mA output of a typical smoke detector has been converted through data acquisition or software. The current becomes voltage V, and the voltage is converted into concentration value through C=KV. If the coefficient K is set to 1, the value recorded by the software is the original signal voltage. By regressing the results of voltage and isokinetic sampling, the response coefficients can be obtained. The quadratic regression result is generally C=K0+KV-K1 * V * V. After such regression, there may be very small constant terms that can generally be ignored. Figure 10 shows the correlation between the same set of data using linear regression and quadratic regression.