Online pH sensors are the core equipment for monitoring the acidity and alkalinity of solutions in industrial process control. Their installation location, flow mode, and grounding design directly affect measurement accuracy and equipment lifespan. Below are three core points for analysis:
1、 Installation location selection: Avoid interference and ensure representativeness
Vertical installation priority
The sensor should be inserted vertically into the pipeline or reactor to avoid particle deposition on the surface of the sensitive membrane. If horizontal installation is required, anti sedimentation devices such as inclined 45 ° deflectors should be installed to ensure that the fluid flushes the membrane surface.
Avoid dead corners and turbulent areas
The installation point should be far away from areas that are prone to turbulence or eddy currents, such as pump outlets, valves, elbows, etc., to prevent mechanical impact from damaging the glass film or causing measurement fluctuations. For example, when installing in a pipeline, it is necessary to choose a position where the length of the straight pipe section is ≥ 10 times the diameter of the pipe.
Temperature and pressure adaptation
Ensure that the temperature and pressure at the installation location are within the sensor range. High temperature environment (>80 ℃) requires the use of high-temperature sensors and equipped with cooling sleeves; High pressure conditions (>1MPa) require a pressure resistant design to avoid membrane rupture.
2、 Flow pattern design: optimizing flow velocity and direction
Flow rate control
The ideal flow rate is 0.3-1.5m/s. If the flow rate is too low, it may cause sedimentation to cover the membrane surface, while if the flow rate is too high, it may cause membrane wear. For example, in a sewage treatment plant, it is necessary to stabilize the flow rate at 0.8m/s by adjusting the pump frequency or installing a throttle valve.
Flow design
The fluid should wash the sensor membrane surface from bottom to top and use gravity to assist in removing bubbles. If it is a horizontal flow, an exhaust valve needs to be installed upstream of the sensor to prevent air accumulation and the formation of measurement blind spots.
3、 Grounding system construction: eliminating static electricity and electromagnetic interference
Single point grounding principle
The sensor housing, signal line shielding layer, and transmitter housing need to be connected to the same grounding electrode through low resistance conductors (≤ 4 Ω) to avoid ground loop interference caused by multiple grounding points. For example, in a chemical workshop, the grounding electrode should be buried 1.5 meters underground, away from power cables.
Shielding layer treatment
The shielding layer of the signal line needs to be grounded at one end of the transmitter and suspended at the other end to prevent electromagnetic induction noise from entering. If the transmission distance is greater than 100m, twisted pair shielded cables should be used and signal isolators should be installed.
Anti-static measures
In flammable and explosive environments, sensors need to be connected to anti-static grounding grids through electrostatic grounding clamps with a resistance value of ≤ 100 Ω to avoid safety accidents caused by static sparks.
4、 Key points for maintenance and calibration
Regularly perform two-point calibration using standard buffer solutions (pH 4.01, 7.00, 10.01), and clean the membrane surface with deionized water before calibration. If scaling occurs on the membrane surface, soak it in a 1% hydrochloric acid solution for 5 minutes. Scratching with hard objects is strictly prohibited. The lifespan of sensors is usually 1-3 years, and they need to be replaced in advance according to the working conditions.
Through scientific installation, reasonable flow design, and reliable grounding, the online pH sensor can ensure long-term stable operation with a measurement error of<± 0.02 pH, providing accurate data support for process control.