Potentiometric & Ion-Selective Theory (pH, ORP, and ISE Probes)
Every single one of our potentiometric sensors operates on Nernstian electrochemical principles. Take our standard pH probe (QT-W201PS), the Redox ORP sensor (QT-W210OS), or specialized ion probes like Ammonia (QT-W206AN), Calcium (QT-W218CI), Nitrate (QT-W337NS), Nitrite (QT-W225NS), Chloride (QT-W220CI), and Potassium (QT-W219PI).
These sensors do not require chemical indicators. Instead, they feature selective glass bulbs or solid-state polymer membranes that interact exclusively with your target ion. When the target ions press against the active membrane, a localized electrical charge builds up. The probe measures the voltage difference between this active membrane and a highly stable internal reference junction, translating the voltage directly into a concentration reading.
Amperometric & Conductometric Theory (DO, Conductivity, and Sanitizer Probes)
For tracking dissolved gases and sanitizing chemicals, we rely on direct electron transfer and electrical field measurements.
- Conductivity and Salinity: Our Conductivity sensor (QT-W203ES) and Salinity probe (QT-W209SS) apply a small alternating current across internal electrodes. The sensor measures how easily this electrical charge travels through the dissolved salts, yielding an instantaneous conductivity reading that stays incredibly steady without drifting out of whack.
- Amperometric Diffusion: Our traditional polarographic Dissolved Oxygen sensor (QT-W202DO), Residual Chlorine probes (QT-W211RC and the constant-voltage QT-W750RC), Ozone sensor (QT-W750OZ), and Chlorine Dioxide probe (QT-W750CD) apply a precise, constant voltage to a noble metal cathode. As the target chemical diffuses through the membrane, it undergoes an oxidation-reduction reaction at the cathode. The resulting electrical current is directly proportional to the chemical concentration, giving you instant, real-time control over your sanitization loops.
Optical Absorbance Theory (Beer-Lambert COD and Chroma Probes)
For our light-beam probes, we throw out wet chemistry completely and rely on the Beer-Lambert law. Take our COD sensor (QT-W207CS) or the Chroma color analysis probe (QT-W230CS).
These sensors shine a specific light beam straight through the dirty process stream. Because organic pollutants absorb ultraviolet light at a wavelength of 254 nm like a dry sponge, the sensor simply measures how much light gets blocked on its way to the internal receiver. The probe translates this light absorption into a COD concentration value in real time, with no boiling sulfuric acid, no toxic mercury, and absolutely zero waiting around for digestion.
Nephelometric Light Scattering Theory (Turbidity, TSS, and MLS Probes)
To track suspended particles without filtering or drying samples, our sensors utilize light scattering principles.
- 90-Degree Scattering: Our standard Turbidity sensor (QT-W336TB) and TSS probe (QT-W214TS) shine an infrared beam into the water. The light bounces off floating dirt, and a detector positioned at 90 degrees measures the scattered light intensity to calculate turbidity values.
- Laser Nephelometry: For ultra-pure drinking water, our Laser Turbidity sensor (QT-W204LT) uses a highly focused laser source to capture trace particulates with extreme sensitivity.
- Backscattering: For reading through thick activated sludge in aeration tanks, our Mixed Liquor Suspended Solids probe (QT-W215MS) utilizes backscattering, measuring the light that bounces directly backward to prevent the sensor from getting blinded.
Luminescence & Fluorescence Spectroscopy Theory (Fluor DO, Algae, and Hydrocarbon Probes)
For specialized organic tracking, our optical probes use light-induced excitation of active molecules.
- Fluorescence DO Phase Shift: The Fluorescence Dissolved Oxygen sensor (QT-W338FO) shines a blue light onto an active luminescent layer on the sensor tip. Oxygen molecules in the water quiet down that glow. The probe measures the phase shift of the reflected light, providing a highly stable dissolved oxygen reading that never consumes oxygen or drifts.
- Pigment Fluorescence: Our Chlorophyll probe (QT-W212CS) and Blue-Green Algae sensor (QT-W213BA) shine specific excitation wavelengths into the water, causing live algae pigments to fluoresce. The sensor captures the emitted light, telling you exactly how much algae is present before your intake filters get clogged.
- Trace Hydrocarbon Fluorescence: The Oil in Water probe (QT-W216OW) targets the aromatic hydrocarbons in oil, triggering a localized fluorescent response to detect trace leaks before they damage your filtration membranes.
Quick Reference: Sensor Model Specifications
| Sensor Model | Targeted Parameter | Technical Range & Accuracy | Measurement Theory |
|---|
| QT-W201PS | pH | 0 to 14 pH (±0.01 pH) | Potentiometric glass-electrode |
| QT-W210OS | ORP | -2000 to +2000 mV (±1 mV) | Redox potential |
| QT-W203ES | Conductivity | 0 to 2000 µs/cm (±1% FS) | Alternating current conductometry |
| QT-W202DO | Polarographic DO | 0 to 20 mg/L (±5% FS) | Membrane-based amperometry |
| QT-W211RC | Residual Chlorine | 0 to 20 mg/L (±1 mV) | Amperometric reduction |
| QT-W750RC | Constant Voltage Chlorine | 0 to 20 mg/L (±1 mV) | Amperometric reduction |
| QT-W750OZ | Ozone | 0 to 20 mg/L (±1 mV) | Direct amperometry |
| QT-W750CD | Chlorine Dioxide | 0 to 20 mg/L (±1 mV) | Direct amperometry |
| QT-W338FO | Fluorescence DO | 0 to 20 mg/L (±1 mV) | Luminescent phase decay |
| QT-W207CS | COD | 0 to 500 mg/L (±5% FS equiv. KHP) | UV-Vis absorption |
| QT-W336TB | Turbidity | 0 to 4000 NTU (±5% FS) | 90-degree infrared scattering |
| QT-W204LT | Laser Turbidity | 0 to 20 NTU (±2% FS) | Laser nephelometry |
| QT-W215MS | MLS (Sludge) | 0 to 30 g/L (±5% FS) | Near-infrared backscattering |
| QT-W214TS | TSS | 0 to 30 mg/L (±5% FS) | Near-infrared backscattering |
| QT-W230CS | Chroma Color | 0 to 500 PCU (±5% FS) | Optical spectrophotometry |
| QT-W216OW | Oil in Water | 0 to 50 PPM (±3% FS) | UV fluorescence spectroscopy |
| QT-W212CS | Chlorophyll | 0 to 500 ug/L (±5% FS) | Fluorescence pigment excitation |
| QT-W213BA | Blue-Green Algae | 0 to 300,000 cells/ml (±5% FS) | Fluorescence pigment excitation |
| QT-W206AN | Ammonia Nitrogen (NH3-N) | 0 to 18,000 mg/L (Slope: 56±4 mV) | Gas-permeable potentiometric ISE |
| QT-W218CI | Calcium Ion (Ca2+) | 0 to 40,000 ppm (Slope: 56±4 mV) | Solid-state potentiometric ISE |
| QT-W209SS | Salinity | 0 to 70 PSU (±1% FS) | Alternating current conductometry |
| QT-W337NS | Nitrate Nitrogen (NO3-N) | 0 to 100 mg/L (±5% FS) | Solid-state potentiometric ISE |
| QT-W225NS | Nitrite Nitrogen (NO2-N) | 0 to 100 mg/L (±5% FS) | Solid-state potentiometric ISE |
| QT-W220CI | Chloride Ion (Cl-) | 0 to 100 mg/L (±5% FS) | Solid-state potentiometric ISE |
| QT-W219PI | Potassium Ion (K+) | 0 to 100 mg/L (±5% FS) | Solid-state potentiometric ISE |
Consumable Upkeep: The Reality of Sensor Lifespans
Let's call it like it is: even though these direct, reagent-free probes save you from buying massive boxes of testing chemicals, they still need a little bit of love to keep their readings spot on. You can't just throw them in a pipe and forget about them for five years.
Calibration Potions
Sensors naturally get a bit lazy over time. You've got to dunk them in fresh, certified calibration liquids (like pH buffers or conductivity standards) to reset their baseline. Some smart controllers can do this automatically, but if you're dealing with really nasty industrial runoff, a quick manual dunk is the safest bet to make sure your data is true.
Keeping the Muck Off
Gunk, slime, and biological algae love to stick to sensor tips and block the light or choke the membranes. Multi-parameter arrays and turbidity probes need automatic cleaning wipers to physically scrub the glass clean (because nobody wants to crawl into a freezing cold holding tank on a Friday afternoon just to wipe slime off a lens!).
The Replacement Cycle
Optical probes (like our UV COD or glowing DO sensors) are incredibly long-lasting because they don't use up their internal parts. But electrochemical tips and ion membranes are chemically active, meaning they will eventually wear out. Keeping a few spare replacement tips on the shelf is the ultimate insurance policy against sudden system downtime, keeping your data satisfyingly spot on.
