Conductivity – Description

Electrical Conductivity (EC) describes how easily an electric current can pass through a substance, especially liquids containing dissolved ions.

⚡ 1. Definition

Electrical conductivity is the ability of a solution to carry electric charge, mainly through the movement of:

• Cations (+ ions)
• Anions (− ions)

The more ions present, the higher the conductivity.

📏 2. Units

• Siemens per meter (S/m) — SI unit
• Common practical units for liquids:
  • µS/cm (microsiemens per centimeter)
  • mS/cm (millisiemens per centimeter)

🔬 3. Principle of Measurement

Conductivity is measured by applying an AC voltage between two electrodes and measuring the resulting current:

\sigma = \frac{1}{\rho}

Where:

• σ (sigma) = electrical conductivity
• ρ (rho) = resistivity of the material

🌊 4. In Liquids (Electrolytic Conductivity)

Conductivity depends on:

• Ion concentration (more salts → higher EC)
• Ion mobility (temperature dependent)
• Type of dissolved substances (Na⁺, Cl⁻, Ca²⁺, etc.)

📊 5. Typical Conductivity Ranges

• Ultra-pure water: ~0.05 µS/cm
• Distilled water: ~0.5–10 µS/cm
• Drinking water: ~50–800 µS/cm
• River water: ~50–1500 µS/cm
• Seawater: ~50,000 µS/cm (≈ 50 mS/cm)

🌡️ 6. Temperature Effect

• Conductivity increases about ~2% per °C rise
• Standardized to 25°C reference temperature

🧪 7. Measurement Setup

• Conductivity cell (electrodes): graphite, platinum, or stainless steel
• Cell constant (K): defines geometry of electrodes
• AC excitation: prevents electrode polarization
• Often combined with TDS (Total Dissolved Solids) estimation

🧭 8. Key Characteristics

• Direct indicator of dissolved ionic content
• Does not identify specific ions
• Widely used in:
  • water quality monitoring
  • hydroponics
  • industrial process control
  • environmental testing