Near-Infrared Online Moisture Measurement System for Paper

What is the Near-Infrared Online Moisture Measurement System for Paper?

A near-infrared online moisture system mounts across the paper machine and measures water content continuously at the water absorption bands. It provides full-width moisture profiles for automatic control of drying and for quality documentation.

Overview

A near-infrared source and detector pair, or a scanning head, measures reflected or transmitted radiation at wavelengths where water absorbs strongly, typically around 1.45 and 1.94 µm, with reference wavelengths used to compensate for basis weight, filler and lamp ageing. Because penetration is limited to a few hundred micrometres, the measurement represents the sheet surface but is closely related to the total moisture of a thin sheet. Several heads can be spaced across the web for a simultaneous profile, or a single head can traverse, and results feed a control loop that adjusts steam pressure or dryer speed. Calibration uses the oven reference method and is grade specific, and the system requires a clean optical path, calibrated standards and a periodic verification routine.

How does it work?

All moisture methods compare the mass of water in the sample with either the wet mass or the dry mass, and the chosen reference must always be reported because moisture content and dry matter content give different numbers. The reference method dries a specimen to constant mass in an oven at a specified temperature and calculates the mass loss. Halogen drying performs the same measurement quickly on a built-in balance, using a halogen radiator for faster and more uniform heating, and requires correlation with the oven method for each paper grade. Karl Fischer titration is a chemical method: iodine reacts quantitatively with water, and the endpoint is detected electrochemically, so it measures water specifically and is unaffected by other volatile substances. Microwave and near-infrared instruments measure indirectly through absorption or dielectric response and need calibration against a reference method.

What are the key features?

• Water absorption band measurement near 1.45 and 1.94 µm
• Reference wavelength compensation for basis weight
• Full-width profile from multiple heads or scanning
• Signal output for dryer control loops
• Automatic traversing with machine and cross direction mapping
• Grade-specific calibration with reference method data

What are the technical specifications?

A typical near-infrared online moisture measurement system for paper configuration offers wavelength bands of About 1.45 µm and 1.94 µm water bands, moisture range of 2–20%, accuracy after calibration of ±0.2% absolute typical, measurement spot of 10–30 mm, scan speed of Up to 20 m/min traverse and web widths of Up to 8 m with multiple heads. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Near-Infrared Online Moisture Measurement System for Paper is used in automatic dryer control on paper machines, full-width moisture profile monitoring, cross direction moisture variability reduction and continuous quality record for each reel. Across the wider Moisture Testing class, laboratories also deploy it for incoming moisture checks on pulp and recovered paper, machine-direction moisture control during papermaking and finishing and converting moisture verification.

Which standards and certifications apply?

Relevant standards and methods include ISO 287, ISO 638, ISO 760, TAPPI T412, ASTM D644, ASTM D6869 and IEC 61010-1. Certification candidates for this model are CE and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Sample handling dominates the uncertainty because paper equilibrates with the surrounding air within minutes. Cut sealed specimens, weigh them quickly in a closed container, and record the temperature and relative humidity of the laboratory, since the standard equilibrium condition defines the moisture of a well-conditioned sheet. Oven temperature, drying time and the use of a desiccator before weighing must follow the method, and the balance should be checked with certified masses. For indirect instruments, recalibrate whenever furnish, coating, grade or basis weight changes, and keep the reference results used to build the calibration. Store paper samples away from heat and direct sunlight before testing.

How do I select the right Near-Infrared Online Moisture Measurement System for Paper?

Specify an online near-infrared system when moisture must be controlled continuously rather than verified afterwards, or when cross-direction profiles are needed to improve uniformity. Confirm the installation positions, the number of heads required for your web width, the output protocol of your control system and how calibration data will be maintained as grades change.

How does it compare with other Moisture Testing variants?

Choose the reference oven method when a specification value is required, since almost all paper moisture standards are written around it. Select a halogen instrument for routine control where speed matters, but establish and document the correlation with the oven method for each grade, including for coated and highly filled papers. Karl Fischer titration suits samples where volatile substances other than water are present, such as papers containing solvents, and can be combined with an oven accessory for solid samples that do not disperse. Microwave and near-infrared instruments are chosen for production use: the near-infrared systems mount on the machine and measure across the full web width continuously, while microwave instruments suit bale and stack checking on the floor.