LEVEL DETECTION CIRCUITRY
location. Using relays, this system provides alarms on high and low level. It may also provide
control functions such as repositioning a valve and protective features such as tripping a pump.
Density of the fluid whose level is to be measured can have a large effect on level detection
instrumentation. It primarily affects level sensing instruments which utilize a wet reference leg.
In these instruments, it is possible for the reference leg temperature to be different from the
temperature of the fluid whose level is to be measured. An example of this is the level detection
instrumentation for a boiler steam drum. The water in the reference leg is at a lower temperature
than the water in the steam drum. Therefore, it is more dense, and must be compensated for to
ensure the indicated steam drum level is accurately indicated.
Ambient temperature variations will affect the accuracy and reliability of level detection
Variations in ambient temperature can directly affect the resistance of
components in the instrumentation circuitry, and, therefore, affect the calibration of
electric/electronic equipment. The effects of temperature variations are reduced by the design
of the circuitry and by maintaining the level detection instrumentation in the proper environment.
The presence of humidity will also affect most electrical equipment, especially electronic
equipment. High humidity causes moisture to collect on the equipment. This moisture can cause
short circuits, grounds, and corrosion, which, in turn, may damage components. The effects due
to humidity are controlled by maintaining the equipment in the proper environment.