This method uses mercury as a conductor. A number of conduct rods are placed at various liquid levels. As head h increases, the rising level of mercury above the datum, shorts successive resistors R and increases the value of h directly.
Advantages 1. Direct reading is possible 2. Simple 3. cost-effective measuring principle 4. Multi-point detection with one process connection
Disadvantages. 1. The liquid being measured must be conductive in nature. 2. The sensor tips deteriorate over time and can need periodic cleaning to keep them from fouling 3. Deposition of contaminate will give error in reading