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What is used to measure the specific density of electrolyte in a battery?
Thermometer
Tachometer
Multi-meter
Hydrometer
Hydrometer
A hydrometer is an instrument specifically designed to measure the specific gravity (relative density) of liquids. In lead-acid battery maintenance, it is used to determine the state of charge by measuring the density of the sulfuric acid electrolyte.
A hydrometer is an instrument specifically designed to measure the specific gravity (relative density) of liquids. In lead-acid battery maintenance, it is used to determine the state of charge by measuring the density of the sulfuric acid electrolyte.
SG=╧БwaterтАЛ╧БelectrolyteтАЛтАЛ тАФ The definition of specific gravity as the ratio of electrolyte density to pure water density.
The hydrometer operates on Archimedes' Principle, which states that a floating body displaces its own weight of the liquid in which it floats. As the electrolyte's concentration of sulfuric acid changes during charge (higher density) or discharge (lower density), the buoyant force changes. Consequently, the calibrated float sits at different levels, allowing the user to read the specific gravity value on the graduated stem.
A fully charged lead-acid battery typically has a specific gravity between 1.260 and 1.280.
A discharged battery typically shows a specific gravity near 1.100 to 1.150.
Temperature compensation is often required since electrolyte density changes with temperature.
Hydrometers must be handled carefully to avoid spills of corrosive sulfuric acid.
Simple and reliable method for state-of-charge determination
Non-electronic, no power source required for measurement
Cost-effective tool
Requires manual withdrawal of electrolyte
Risk of acid exposure
Not suitable for sealed (VRLA/AGM) batteries
Lead-acid battery maintenance in substations
Automotive battery health checks
UPS battery system diagnostic monitoring
Thermometer: Measures temperature, not density.
Tachometer: Measures rotational speed of motors/generators.
Multi-meter: Measures voltage, current, or resistance, but cannot directly measure fluid density.
D is correct тАФ The hydrometer measures the specific density (specific gravity) of the electrolyte, which indicates the state of charge of the battery.
Always remember that for maintenance, voltage measurements alone can be misleading; checking electrolyte density via hydrometer provides a more accurate picture of chemical state.