Moisture Measurement in Gypsum Board

Process Sensors will be attending the 9th Global Gypsum Conference for the global trading, marketing, production and processing technology of gypsum.? An application sheet explaining the importance of moisture measurement in gypsum board follows:

The Importance of Moisture Measurement in Gypsum Board

The durability, strength and hardness of finished board is heavily dependent on moisture content. Measuring moisture content not only improve quality, but ensures ongoing product consistency, resulting in fewer reject boards and saving on rework costs.? RFM-1000, Process Sensors? on-line RF sensor, measures moisture, enabling optimization of the production process through feedback and/or feed forward control of the temperature set point within the different kiln zones. Process optimization maximizes quality product throughput, saving on energy & raw materials and also indirectly on labor and plant costs.

Gypsum Board Production Process

Gypsum (CaSO4.2H2O) is obtained either naturally from gypsum deposits in the ground, or synthetically as a byproduct of another process. Most synthetic gypsum is derived from Flue Gas Desulphurization (FGD) of fossil burning fuel power plants. Board can be manufactured from natural gypsum, synthetic gypsum or a combination of the two. Regardless of the derivation of the gypsum, it is crushed, dried, ground to a fine ?flour,? then calcined to drive off all the chemically combined water as steam. Water and other ingredients, e.g., sand and fire retardants, are added, and the wet mix is pumped to a conveyor whereupon it is sandwiched between 2 layers of paper. The board sets as it?s conveyed towards the kiln, is cut into drying lengths and loaded onto a deck within the kiln. The dryer comprises 3 or 4 temperature zones. Upon exiting the kiln, the board is cut to final length, trimmed then packaged.

Sensor Details & Installation

The RF sensor comprises a 30, 60 or 90cm aluminium antenna with teflon spacers, cabling and operator interface. Temperatures exceeding 50? C necessitate the use of aluminium/ceramic antennae, and 260? C; stainless steel/ceramic antennae. Coax cabling is required for all applications where ambient temperature exceeds 60? C. Sensor mountings are constructed from stainless steel. Owing to the differential expansion coefficient of aluminium and steel with temperature, the aluminium sensor is only fixed at one end within the kiln. The other end is free to expand horizontally eliminating the potential for dryer blockages owing to the sensor bowing upwards. The sensor is located 6mm below the bottom face of the board, and requires good clearance beneath, to allow debris to fall through the open frame enclosure.

RF Moisture Measurement in Gypsum Board

Within the dryer, the sensor is normally located on a representative deck, usually deck 4 or 5 in an 8 deck dryer. Sometimes the sensor is located on a wetter deck to most quickly eliminate the source of reject boards. However, this could cause burning on the drier decks unless the kiln is balanced.


The RFM-1000 generates a RF fringe field of approximately 2 MHz into the board. The board conductance changes with water born dielectric variation, and this produces a raw dielectric value that is directly proportional to the moisture content of the product. Moisture can be measured in the range 0-80%, but will require different calibrations for low, medium and high moisture levels. Radio frequency measurements are not influenced by changes in PH and dissolved salts, but are affected by shifts in distance between product and sensor, density changes and appreciable temperature changes. Pass height variation is not of concern when measuring on the lower edge of the board. Compensation inputs are available for density and temperature changes if required, but all that is typically needed is a change of calibration when switching between products of different thicknesses. The sensor features high speed measurement capability, up to 200 measurements per second, and together with the automatic product loss and return measurement hold signal, this enables the output of individual board moisture averages.

Induction Heating Applications

After unsatisfactory experiences with competitive pyrometers, this nationally known manufacturer of fasteners for aerospace applications recently installed fifteen Model PSC Sirius SI16 pyrometers on their Inductoheat, Ameritherm, and Tocco induction heating machines.

The machines pre-heat high-duty alloy blanks that are then forged into fasteners used in aircraft and space module construction.? The accuracy, precision adjustable focus and laser aiming of the Sirius pyrometer is critical to ensure correct temperature and heat distribution in the blanks.? This is essential to avoid post-forging stresses that could give rise to fastener failure in use.

A company spokesman, who selected the PSC? Sirius SI16?s over the competition, stated that ?The Process Sensors product was the only one that met or? ? exceeded our rigid requirements in the manufacturing environment.? All the pyrometers have performed flawlessly.?

The Application

Induction heating uses high frequency electromagnetic energy to rapidly heat metals. Application constraints typically include confined sighting paths, small targets, variable emissivity surfaces, smoke in the sight path and strong magnetic fields.

The design features of the Sirius pyrometers are aimed at eliminating or minimizing the impact of these factors on the measurement.? The narrow, short wavelength spectral response reduces errors due to variable emissivity.? Adjustable focusing and laser aiming simplify sighting on specific areas of the product, while avoiding partial obstructions in the sight path.? Digital signal processing and careful electronic design minimize magnetic interference.

The Market

Induction heating machines are common across manufacturing industries wherever metals are heat treated or formed.? The fastener industry, auto and aircraft components manufacturing, tool making and
pipe forming, as examples, all use a multiplicity of induction heating systems.

This processing method is also found in less obvious applications such as rebar coating and bearing manufacturing.

Many induction heating OEM?s have traditionally used competitive IR sensors, but it is clear that the high accuracy SI16 with wide temperature range, small spot size, adjustable focus laser aiming, standard analog and digital output capabilities make this the preferred sensor of choice in the induction heating marketplace.

Model No.: PSC?s Sirius SI16-0300-1300-1-2-2-5-1-A

Temperature range: 572?F to 2372?F ( 300 to 1300?F )

Process Sensors Attends SNAXPO 2009

Process Sensors attended the SNAXPO 2009 Show held March 29-April 1 in Orlando, FL to demonstrate instruments showing the importance of measuring moisture and oil in snack food manufacturing environments.  According to the Snack Food Association, ?More than 100 exhibitors filled the SNAXPO show floor offering new ideas, products and services for snack food company decision makers seeking to build their businesses.?

An application sheet explaining the importance of measuring moisture and oil in potato chips follows.

Measuring Moisture & Oil in Potato Chips

The continuous measurement of moisture prior to packaging is a key consideration in the production of potato chips.? The proper moisture level of finished chips helps guarantee taste, texture and shelf life.

The use of NIR (Near Infrared Reflection) moisture gauges in snack food manufacturing environments has become an accepted technology for monitoring and control.? The on-line measurements are instantaneous and non-contact.? Any change in moisture level can be immediately recognized by the use of a Process Recorder, eliminating the potential for customer quality complaints or waste.

NIR can also be used to measure oil content, along with moisture.? The oil measurement is most often done at-line as a quality indication prior to packaging.

Chip Manufacturing Process
Potatoes are peeled, sliced and de-starched prior to Frying and Seasoning. Measurements of oil and moisture are typically made shortly after the exit of the Fryer. Moisture measurement at the exit of the Fryer can be used to optimize moisture %, this results in greater product consistency, longer shelf-life and less waste material.

Transmitter Installation
PSC moisture transmitters should be located after the fryer outlet, over the vibrating conveyor.? The transmitter should be mounted 10? from the surface of the potato chips.? Heat at the fryer outlet can create very high temperatures.? If the transmitter must be located close to the outlet of the fryer, it is important to consider cooling.

The MCT330SF moisture transmitter is designed to measure moisture, oil and product temperature in a food processing environment. The transmitter is housed in a stainless steel enclosure and employs a food grade optical window. The MCT is optimized with filter combinations to measure moisture and oil at the same time.? The viewing window in the sensor is a food grade polymer.? The stainless steel housing is sealed so that the NIR sensor can tolerate a wash-down environment.

The MCT-330SF is fitted with an air purge assembly to prevent oil or moisture from depositing on the sensor?s lens.? The Stainless Steel Enclosure can also be fitted with a Vortex cooler in the event of a very elevated temperature environment.

Measurement Performance
Moisture measurement in potato chips is a very well understood and documented application. NIR wavelengths, algorithms, and sensor optical parameters are pre-set at the PSC factory.

A calibration is entered into the MCT-330SF at the PSC factory.? There is no calibration required after installation on the processing line.

It is important to locate the MCT so that there is always product beneath the NIR sensor.? The measurement works by detecting reflected light.? The light must be reflected off of the product, not the vibrating conveyor!