Falling load generator
When we are setting up an exposure parameter, for a particular part of the body to be exposed, we follow a three parameter setting, i.e KVp, mA and time or two parameter setting, i.e KVp and mAs. In case of two parameter setting, KVp is elected and then mAs is selected. The mAs setting automatically selects mA and exposure time. The mA and the time selected are fixed throughout the exposure duration.
In a Falling load generator, when a mAs is selected, the generator starts with maximum mA possible based on the heat-loading potential of the x-ray tube. When the tube reaches its maximum heat load, the generator automatically reduces the mA to the next lower level, that the tube can handle and the exposure continues with lower levels of mA till it delivers the set mAs.
With this technique the generator always uses the shortest exposure time possible to deliver the set mAs.
Please see the graphical representation of the technique for easy understanding: