Step 1: Understanding the Concept:
This question asks for the specific term used to define a type of grain loss during the operation of a mechanical thresher. Thresher efficiency is evaluated by measuring different types of losses.
Step 2: Detailed Explanation:
Let's define the different types of losses in a thresher:
Threshing Action: The core of a thresher is the threshing cylinder and concave. This is where the grain is detached from the straw/panicle by impact and rubbing.
Separation and Cleaning: After threshing, the mixture of grain, straw, and chaff is separated. The straw is typically removed by a straw walker, and the chaff is blown away by a blower/fan, while the grain falls through sieves.
Now let's analyze the loss types:
(A) Cylinder loss (or Un-threshed loss): This refers to the grains that are not detached from the panicles/straw during the threshing action in the cylinder-concave unit. These un-threshed grains then exit the thresher along with the main straw outlet. The question defines the loss as "un-threshed grains from all outlets," which precisely matches the definition of cylinder loss.
(B) Blower loss (or Cleaning loss): This refers to the whole, healthy grains that are blown out of the thresher along with the chaff and other light material by the cleaning fan. This happens if the blower speed is too high.
(C) Sieve loss (or Separation loss): This refers to the free grains that have been threshed but fail to be separated from the straw and exit the machine with the straw from the straw walker or straw outlet.
(D) Visible damage loss: This refers to the percentage of grains that are broken, cracked, or visibly damaged by the mechanical action of the thresher.
Step 3: Final Answer:
The percentage of grains that remain un-threshed and exit the machine is called cylinder loss or un-threshed loss. Therefore, option (A) is the correct answer.