Endpoint can be defined as a target particle size mean or distribution.
a) Power Consumption. Power consumption of the mixer motor for end-point determination and scale-up is widely used because the measurement is economical, does not require extensive mixer modifications and is well correlated with granule growth . Intragranular porosity also shows some correlation with power consumption. Normalized work of granulation (power profile integrated over time) can accurately determine endpoints and is correlated well with properties of granulates.
b) Impeller Torque. Direct torque measurement requires installation of strain gauges on the impeller shaft or on the coupling between the motor and impeller shaft. Since the shaft is rotating, a device called a slip ring is used to transmit the signal to the stationary data acquisition system.
c) Torque Rheometer. A torque rheometer provides an off-line measurement of torque required to rotate the blades of the device and can be used to assess rheological properties of the granulation. It has been extensively used for endpoint determination. The torque values obtained have been termed a “measure of wet mass consistency” .
d) Reaction Torque. As the impeller shaft rotates, the motor tries to rotate in the opposite direction, but does not because it is bolted in place. The tensions in the stationary motor base can be measured by a reaction torque transducer.
e) Other Possibilities. When agglomeration is progressing very rapidly, neither power consumption nor torque on the impeller may be sensitive enough to adequately reflect material changes. Some investigators feel that other measurements, such as torque or force on the impeller blades, may be better suited to monitor such events. There are other ideas floating around—for example, use of neural networks to describe and predict the behavior of the wet granulation  or control of the endpoint by a rapid image processing system . A technique for measuring tensile strength of granules, in addition to power consumption measurement, to facilitate optimal endpoint determination, has been described by Betz, Bürgin and Leuenberger. Powder flow patterns in wet granulation can be studied using positron emission particle tracking .
a) Acoustic. Applicability of piezo-electric acoustic emission sensors to endpoint determination has been studied since the beginning of this century . The technique is very promising, especially since it is non-invasive, sensitive and relatively inexpensive. Granulation process signatures obtained with an acoustic transducer can be used to monitor changes in particle size, flow and compression properties.
b) Near-Infrared (NIR). Use of a refractive NIR moisture sensor for endpoint determination of wet granulation has been described by several authors . There are technological challenges associated with this approach, as the sensor can only measure the amount of water at the powder surface.
c) FBRM. Focused beam reflectance measurement (FBRM) is a particle-size determination technique based on a laser beam focusing in the vicinity of a sapphire window of a probe . The beam follows a circular path at speeds of up to 6 m/s. When it intersects with the edge of a particle passing by the window surface, an optical collector records a backscatter signal. The time interval of the signal multiplied by the beam speed represents a chord length between two points on the edge of a particle. The chord length distribution (CLD) can be recalculated to represent either a number or volume-weighted particle size distribution. In many cases, CLD measurements are adequate to monitor dynamic changes in process parameters related to particle size and shape, concentration and rheology of fluid suspensions.