Usually, the equipment used for online water quality monitoring uses distilled water as zero calibration solution. Generally speaking, in operation, equipment should be tested for zero, range and repeatability before leaving the factory.
Definition of zero drift:
At the beginning of the detection period, the zero and range values of the instrument are calibrated manually or automatically, and the initial analog zero and range readings are recorded. Measure (manually or automatically) and record zero and range readings every 24 hours; Then calibrate the zero and range values of the instrument and record the zero and range readings; Continuous 168 hours (7 days). Calculate zero drift and range drift according to (3)-(6):
A. zero drift:
Δ δZ = sub -Z0(3)
ZD =δZmax/r× 100%………………………………………………(4)
Where: the initial value of zero reading;
Zi—— the ith zero reading;
ZD- zero drift;
Δ z-absolute error of zero drift;
Δ δ zmax-the maximum absolute error of zero drift;
R refers to the full-scale value of the instrument.
First of all, there are many reasons for zero drift, which can also be reduced through daily maintenance and calibration. On-line equipment for sewage treatment is generally installed at the water outlet, generally industrial sewage and domestic sewage, and it is necessary to determine whether it has an impact on water quality according to the process. There are the following drift reasons for reference only:
1. The laboratory generally uses distilled water to test the zero drift. After a period of field operation, the measuring cell and detector will be polluted, and in some cases, positive drift will occur, which will lead to baseline drift when measuring low concentration data and produce larger data.
2. The aging of optical components and the attenuation of internal voltage or photometric test will cause the baseline of zero drift to move down, resulting in the measured value being low or directly unmeasurable. At this time, it is necessary to replace components or instruments and recalibrate the zero point.
3. Under certain circumstances, there is also the influence of reagents. If there is no standard reagent preparation, it will also have different degrees of influence on the instrument. There is also the purity of the reagents used, and the determination results of several prepared reagents such as analytical purity, excellent purity and chemical purity are not exactly the same.
The above views are for reference only. If you have any questions, please ask.