Agriculture Reference
In-Depth Information
standard (ASAE S530.1 AUG2007) the temperature sensor for the system is to be
located in the hot air line immediately (3 m maximum) ahead of the mix-point where
seed cotton is first exposed to the heated air. The mix-point air temperature should
not exceed 177°C (Hughs et al., 1994; ASABE, 2008).
Seed cotton harvested with low fiber moisture may need moisture added before
fiber-seed separation and lint cleaning to reduce fiber damage caused by the aggres-
sive mechanical actions in the gin stand and lint cleaners, or to stabilize weight at the
bale press. Two approaches are widely used to restore the moisture in cotton fiber.
One is to directly spray liquid water on the cotton. The other is to use humidified air
to moisten cotton. Systems using these approaches are commercially available and
are in use. However, those systems must be used properly with careful calibration
and maintenance so that fiber is not overmoistened.
Accurate measurement of cotton moisture is an essential requirement for proper
management of cotton moisture. The most commonly used approaches for mea-
suring cotton fiber moisture are gravimetric, chemical, spectroscopic, and electric
methods (Rodgers et al., 2009).
The gravimetric method is the standard for determining cotton fiber moisture
content, and other methods use the gravimetric method as the reference. The gravi-
metric method uses an oven to dry a cotton sample to remove its moisture content.
The sample is weighed before and after drying, and the mass difference between
initial and oven-dried masses is calculated. The moisture content (wet basis) of the
sample is the ratio of the mass difference to the initial mass. Although the gravimet-
ric method is fairly accurate, it is not feasible for real-time process control because
of the long measurement time required.
The primary chemical method for determining cotton fiber moisture content is
the Karl Fischer (KF) titration measurement of moisture extracted from the fiber
(Gordon et al., 2010). The KF titration measurement is based on the KF reagent,
which reacts selectively to water. Automatic moisture measurement instruments
using KF titration are commercially available. However, they are expensive and also
not practical for online moisture measurement because of their slow response.
Spectroscopic methods can be used to determine moisture content by measur-
ing the absorption of electromagnetic energy by water molecules. Water absorption
occurs at many wavebands across the electromagnetic spectrum, but strong bands
are in the NIR region, including bands near 1450 and 1950 nm. As electromagnetic
waves themselves, microwaves have been used to measure cotton bale moisture con-
tent. Microwave moisture measurement systems include a microwave emitter and a
receiver. In a transmission-based system the emitter is placed at one side of the bale,
whereas the receiver is aligned with the emitter at the opposite side. Microwave
energy from the emitter passes through the bale to the receiver, and some microwave
energy is lost by absorption of water in the cotton. The energy reduction is used as a
measure of cotton moisture content of the bale. A major advantage of spectroscopic
methods is that they are fast, making it possible for use in real-time process control.
Some spectroscopic instruments for online cotton lint moisture measurement are
commercially available.
Electrical methods for measuring cotton moisture content mainly involve
resistance-based and dielectric-based sensors. The sensors detect impedance or
