Installing a Total Nickel Online Monitor

Installing a total nickel water quality automatic monitor is not simply a matter of fixing the instrument in place. Two risks shape the entire procedure: adsorption and contamination of nickel on tubing surfaces, and bubble interference in the optical detection path. Installation quality directly determines whether later data can pass practical sample comparison, so each step should be organized within the framework of HJ 353–2019.

Site selection comes first. The instrument should be placed in a ventilated, shaded, dust-free indoor environment, away from strong electromagnetic and vibration sources such as variable-frequency drives and main distribution cabinets. The sampling point should be located where the discharge flow is well mixed, with the sampling head submerged below the water surface but well above the bottom to avoid drawing in sediment. The distance from the station to the sampling point should be kept as short as practicable; a long line increases sample residence time and the opportunity for nickel adsorption on the tube wall.

Mechanical fixing must be level. A floor-standing cabinet should be mounted vertically on a solid, flat base and checked with a spirit level, so that internal pumps and valves are not subjected to uneven stress. Sufficient clearance should be left at the front and rear for maintenance, and around the digestion module for heat dissipation and operation. Wiring ports should be sealed, with additional rain protection for outdoor or damp locations.

The tubing system is the most project-specific part of a total nickel installation. PVC and ordinary rubber tubing should not be used, because they tend to adsorb nickel ions. PTFE or silicone tubing with an adequate inner diameter should be selected to reduce blockage and wall retention. A filter should be installed on the sampling line, with pore size chosen according to the suspended solids content, to prevent particles from entering the reaction cell. The line from the station to the sampling point should be laid with a downward slope so that water can drain by gravity when the pump stops, limiting sediment deposition and biofilm growth. Fluororubber seals should be used at all connections to prevent leakage and air ingress.

Electrical and communication installation should follow the principle of separating power and signal lines. The instrument should be supplied from an independent stabilized power source, with proper grounding. Power cables and RS485 or 4–20 mA signal cables should be routed in separate conduits, and shielded twisted-pair cable should be used for signals to reduce electromagnetic interference with the photometric baseline.

After physical installation, leak testing and air purging are necessary before calibration. Start manual sampling mode and check all tubing connections, valves, and the digestion cell for leakage or air ingress. Then purge air from the water path and adjust the peristaltic pump so that sample and reagent volumes are stable and uniform. If bubbles remain, they will enter the colorimetric light path and cause sharp fluctuations in absorbance, distorting the calibration curve.