Residual Chlorine Sensor

A: Polarographic (membrane-covered amperometric) sensors use a gas-permeable membrane and an electrolyte; dissolved chlorine diffuses through the membrane to a working electrode held at a fixed potential. They measure free chlorine, require periodic membrane/electrolyte replacement, and suit lower-conductivity media. Potentiostatic (membrane-free / gel-covered amperometric) sensors apply a fixed electrode potential in direct contact with the sample, have no consumable electrolyte or membrane, respond faster and require lower maintenance; they also measure free chlorine (HOCl). Selection depends on maintenance budget, media fouling level and required response time.

A: Free chlorine in water exists as hypochlorous acid (HOCl, active) and hypochlorite ion (OCl-, less active), and the ratio shifts with pH (mainly pH 5.5-8.5). For accurate free-chlorine control over a varying pH range, pH compensation is recommended; combined pH+free-chlorine sensors compensate automatically. If pH is stable, a pH-compensation-free free-chlorine probe is acceptable.

A: Typical minimum detection limit for membrane-free potentiostatic and membrane amperometric free-chlorine probes is approx. 0.005-0.01 mg/L (5-10 ug/L). Confirm the exact figure from the model datasheet; total-chlorine probes generally have a higher detection limit.

A: Yes. Most residual chlorine sensors integrate a Pt100 or NTC temperature element and provide automatic temperature compensation (ATC), since chlorine reaction rate and membrane permeability depend on temperature. ATC improves accuracy across seasonal and process temperature swings.

A: Typically 40-45 C continuous for amperometric free-chlorine probes. Short-term peaks up to about 60 C are possible, but sustained high temperature accelerates membrane aging, electrolyte consumption and electrode fouling, reducing service life.

A: For flow-cell inline installation, typical maximum working pressure is 3-6 bar (0.3-0.6 MPa), depending on the sensor body and the matched flow cell rating. Verify both the sensor and flow cell pressure limits before piping selection.

A: Yes. Digital models output RS485 Modbus RTU and can be integrated directly into PLC/DCS via standard function codes; combined with a matched transmitter, you can read mV, mg/L, temperature and diagnostic status.

A: Yes. The standard thread is PG13.5 and the probe is compatible with common flow cells (e.g., CCA250-type); confirm the flow cell body material and sealing ring for chemical compatibility with the process medium.

A: Typically every 1-3 months depending on chlorine concentration, fouling and temperature; replace when the calibration slope drifts or response time slows. Higher chlorine loads and dirty media shorten the interval.

A: Yes, free-chlorine probes are suited to pool circulation loops, ideally paired with pH compensation. Organics, UV and bather load cause fouling, so regular cleaning and periodic recalibration are required for stable long-term operation.

A: Yes within the working pH window, but accuracy depends on pH because HOCl/OCl- speciation changes with pH. In variable-pH water (e.g., pH 5.5-8.5), use a pH-compensated free-chlorine sensor or a combined pH+chlorine unit for reliable readings.

A: On-site calibration is commonly done by the DPD (N,N-diethyl-p-phenylenediamine) colorimetric comparison on a grab sample, or by dosing a standard chlorine stock solution to produce a known free-chlorine concentration. Use a two-point check (zero and a working standard) when process accuracy is critical.

A: Direct replacement is possible when thread (PG13.5), signal type (4-20 mA or RS485) and electrical interface match the existing transmitter; otherwise use a matching adapter, cable or the paired transmitter. Verify electrode chemistry compatibility (free vs. total chlorine) before ordering.

A: Sensor body and cable connector are typically rated IP65-IP68 for outdoor/submersible duty; confirm the IP class of the mating connector and terminal enclosure so the whole loop meets the required protection.

A: Generally no. Membrane-free potentiostatic designs have no electrolyte to replace; some models use a replaceable service cap or sensor head for long-term maintenance, which is still far less frequent than membrane-type electrolyte service.

A: Yes. Fouling on the electrode/membrane surface reduces response and accuracy; heavy solids also disturb the hydrodynamic film. Mitigate with regular cleaning, an optional self-cleaning/wiper head, or upstream filtration for turbid streams.

A: Yes, cable length can be customized. For long runs use shielded cable and keep signal attenuation in mind; digital RS485 outputs tolerate longer cable lengths than analog 4-20 mA. Confirm the connector and shielding spec with the manufacturer.