Multi Parameter Meters

Polarographic (and galvanic) DO sensors use a membrane-covered electrode that consumes a small amount of oxygen during measurement and requires periodic membrane replacement and electrolyte refill; optical (luminescent) DO sensors measure oxygen's effect on a luminescent compound's fluorescence and don't consume oxygen or require membrane replacement, generally needing less frequent maintenance, though they typically cost more upfront.

pH and conductivity readings are both temperature-dependent — the same sample can give different raw readings at different temperatures — so meters use automatic temperature compensation (ATC), measuring sample temperature via a built-in or attached sensor and correcting the displayed reading to a standard reference temperature (usually 25°C), ensuring readings are comparable across different sampling conditions.

Calibration frequency depends on use intensity and regulatory requirements, but a common practice is calibrating pH before each day's use or each sampling session, and conductivity/DO on a less frequent but regular schedule (weekly or per the meter's manufacturer guidance) — any meter used for regulatory compliance reporting should follow the applicable program's specified calibration frequency and documentation requirements.

Contacting electrode sensors work well for lower-conductivity, relatively clean samples and are generally lower cost; inductive (toroidal) sensors don't have exposed electrodes to foul and handle higher-conductivity or dirtier samples (like wastewater or brine) more reliably over time, making them preferred for continuous or harsh-condition monitoring.

Some combination probes integrate pH, ORP and temperature sensing in a single probe body, but dissolved oxygen and conductivity typically require their own dedicated sensors due to different measurement principles — a true multi-parameter meter usually has multiple probe inputs or a multi-sensor combination probe rather than one sensor measuring everything.