Different level measuring systems : A Comparison
PRINCIPLE | SYSTEM | CHARACTERISTICS | |
ADVANTAGE | DISADVANTAGE | ||
SIGHT | DIPSTICK | Simple, cheap, instant | Need to remove to read |
SIGHT GLASS | Cheap, fairly foolproof, pressure up to 700 Mpa and 300oC | Need to careful handling, brittle. | |
TAPE/FLOAT | Cheap, can be used with corrosive liquids, but opening for tape. | Low pressure/ atmospheric only. Can Stick. | |
POTENTIOMETER FLOAT | Voltage output as above | Stiction | |
MAGNETIC | As above | Stiction | |
DISPLACERS | SPRING BALANCE | Can be used for interfaces, limited range. | Expensive |
TORQUE TUBE | Most displacer transmitters use this, accurate but limited range. | Limited range. | |
PRESSURE | PRESSURE GAUGE | Cheap, open and closed tank. | Not available readily in low range in H2O. |
BUBBLER METHOD | Can be used for slurries, or corrosive mixtures. | Requires air supply. | |
WEIGHT | LOAD CELLS | Accurate non-contact method. | Need frequent recalibration. |
ELECTRICAL | CONDUCTIVITY | Rugged, requires little maintenance. | Limited to conductive liquids. |
RESISTANCE | Rugged, requires little maintenance. | First few inches not accurate. | |
CAPACITIVE | Rugged and accurate. | Tank must be metal if only probe is used. | |
ULTRASONIC | ECHO TYPE | Non-contact | High pressurize wont work, expensive. |
RADIATION | ABSORPTION | Non-intrusive. | Expensive, not accurate, hazardous source. |
THERMAL | THERMISTOR | New method, cost reasonable. | On/Off only |