- You cannot place a new order from your country (United States).
search
search
HM Digital Electrode Sonde pH for PH-200
The HM Digital Electrode Probe pH for PH-200 is the original SP-P2 replacement sensor restoring measurement capability to your professional pH meter. pH sensors employ a glass membrane that generates voltage proportional to hydrogen ion concentration — a fundamentally different technology from stainless steel EC probes, with inherently shorter operational lifespan. This replacement probe integrates a glass pH sensor, reference element and thermistor for automatic temperature compensation across the 0 to 14 pH measurement range. Tool-free installation takes under five minutes. Two-point calibration with pH 7.01 and pH 4.01 buffer solutions restores factory accuracy. Always store in KCl solution to prevent membrane dehydration. Order from plantandflower.be with fast delivery across Belgium.
HM Digital pH Replacement Probe for PH-200 – Glass Electrode Technology Restored
pH measurement accuracy degrades predictably over time. The glass membrane electrode in your HM Digital PH-200 has a finite operational life determined by membrane thickness, reference electrolyte condition and junction integrity. When calibration no longer compensates for drift, the SP-P2 replacement probe restores factory-level performance at a fraction of full meter replacement cost. Proper maintenance of pH sensors starts with correct storage — keep the electrode in KCl storage solution to preserve membrane hydration and reference stability.
Glass membrane pH sensing: how it works and why it degrades
pH electrodes operate on the Nernst principle. A thin glass membrane develops an electrical potential proportional to the hydrogen ion activity difference between the sample solution and the internal reference electrolyte. This potential, measured in millivolts, is converted by the meter's processor into a pH reading. The glass membrane is intentionally thin to maximise ion sensitivity, but this makes it susceptible to several degradation mechanisms. Repeated exposure to strongly acidic or alkaline solutions gradually etches the membrane surface. Temperature cycling induces micro-stress in the glass structure. Extended dry storage causes irreversible dehydration of the gel layer that facilitates ion exchange. These factors combine to produce progressively slower response times and reduced measurement accuracy that calibration alone cannot correct.
- Glass pH sensor: generates millivolt potential proportional to H+ ion concentration for linear response across the full 0-14 pH range.
- Reference element: provides a stable reference potential against which the pH signal is measured differentially.
- Integrated thermistor: enables automatic temperature compensation from 0 to 50°C, eliminating thermal measurement error.
- Exclusive compatibility: engineered specifically for the HM Digital PH-200 — not interchangeable with other meter models.
Replacement procedure and two-point calibration
Sensor replacement requires no tools. Power off the PH-200, detach the degraded probe and connect the SP-P2 until it locks securely. Power on and initiate two-point calibration for maximum accuracy across the measurement range. Calibrate first with pH 7.01 buffer solution to set the zero point, then with pH 4.01 buffer to define the slope. This two-point procedure corrects both offset and gain errors simultaneously, ensuring accurate readings throughout the 5.0 to 8.0 range critical for hydroponic and soil-based cultivation. Use fresh buffer solution for each calibration — reused buffer introduces contamination that produces systematic calibration error.
Storage protocol: the critical factor in probe longevity
More pH probes fail from improper storage than from measurement wear. The glass membrane must remain hydrated at all times — a dehydrated membrane loses its ion-exchange gel layer permanently and cannot be recovered. Store the electrode in KCl storage solution inside the protective cap between uses. Never use deionised or distilled water for storage: the absence of dissolved salts creates an osmotic gradient that depletes the reference electrolyte. After each measurement, rinse with clean water and replace the cap. Periodic cleaning with electrode cleaning solution removes protein and mineral deposits that slow response time. With disciplined maintenance, expect six to twelve months of reliable service from each replacement probe.
Order the HM Digital pH Replacement Probe for PH-200 from plantandflower.be with fast shipping across Belgium. Restore measurement precision without replacing the entire instrument.
Will the SP-P2 probe work with pH meters other than the PH-200?
The SP-P2 is engineered exclusively for the HM Digital PH-200 pH/Temperature meter. The connector and electronic interface are model-specific. It is not compatible with other HM Digital meters or pH meters from other manufacturers.
Why does a pH probe degrade faster than an EC probe?
pH probes use a fragile glass membrane that interacts electrochemically with hydrogen ions, making it susceptible to etching, dehydration and reference depletion. EC probes use robust stainless steel or platinum pins that simply measure electrical resistance between electrodes, with far fewer degradation pathways.
What happens if I store my pH probe in distilled water?
Distilled or deionised water creates an osmotic pressure differential that draws electrolyte out of the reference element through the junction. This depletes the internal reference solution, causing unstable readings and shortened probe life. Always use KCl storage solution or pH 4 buffer as a substitute.
How do I perform a two-point calibration after installing the new probe?
Immerse the probe in pH 7.01 buffer solution first and calibrate the zero point. Rinse with clean water, then immerse in pH 4.01 buffer and calibrate the slope point. This corrects both offset and gain across the measurement range. Always use fresh buffer solution that has not been previously used or contaminated.