1. pH Meter – Working Principle

• Based on electrochemical measurement.
• Uses a glass electrode and reference electrode.
• When immersed in solution, a potential difference (mV) is generated depending on hydrogen ion (H⁺) concentration.
• The analyzer converts this voltage into pH value (0–14 scale).

2. Conductivity – Working Principle

• Based on the ability of water to conduct electrical current.
• Two or four electrodes apply an AC voltage across the solution.
• The current flow depends on ionic concentration.
• Higher ions → higher conductivity (μS/cm or mS/cm).

3. Chemical Oxygen Demand (COD) – Working Principle

• Measures the amount of oxygen required to oxidize organic matter.
• Water sample is treated with a strong oxidizing agent (like potassium dichromate).
• Organic matter gets oxidized.
• The analyzer measures color change or absorbance using photometric method. Result expressed in mg/L of O₂.

4. Dissolved Oxygen (DO) – Working Principle
Two common methods:
a) Electrochemical (Clark Electrode):

• Oxygen diffuses through a membrane.
• It reacts at the cathode, producing current proportional to DO level.
  b) Optical Method:
• Uses luminescent sensor.
• Oxygen quenches the light signal.
• Change in light intensity/lifetime gives DO concentration.

5. Turbidity – Working Principle

• Based on light scattering principle.
• A light beam passes through water.
• Suspended particles scatter light.
• Detector measures scattered light at 90° (nephelometric method).
• Output in NTU (Nephelometric Turbidity Units).

6. Chlorine – Working Principle
Two methods:
a) Colorimetric Method:

• Chlorine reacts with reagent (DPD).
• Produces pink color.
• Intensity measured photometrically.
  b) Amperometric Method:
• Measures current produced due to chlorine reaction at electrode.
• Current ∝ chlorine concentration.

7. Ammonia – Working Principle

• Typically based on Ion-Selective Electrode (ISE) or colorimetric method.
  ISE Method:
• Ammonia gas diffuses through membrane.
• Changes internal pH of electrode.
• Potential difference corresponds to ammonia concentration.
  Colorimetric Method:
• Ammonia reacts with reagents to form colored compound.
• Analyzer measures absorbance.