Infrared moisture meter

Infrared moisture meters are divided into two major categories:Infrared heating loss-on-drying (laboratory benchtop)、Near-infrared spectroscopy type (online / handheld, non-contact), the principles are completely different, and many people easily confuse them.

I. Two Principles

1. Infrared heating moisture analyzer (thermogravimetric method)

Benchtop laboratory instrument, similar in principle to halogen moisture analyzers, with infrared lamps as the heating source / infrared tubes.

• Principle: Infrared radiation heats the sample, moisture evaporates, and the built-in balance measures the weight difference before and after heating to calculate moisture content.
• Test time:315 min。
• Advantages: Low cost, simple operation;
• Disadvantages: Sample is destroyed; other volatile substances in the sample are counted as moisture, leading to higher results; not suitable for materials that decompose at high temperatures.

2. Near-infrared spectroscopy moisture meter (NIR, industrial online/handheld)

Non-contact, non-destructive testing, the most common on production lines.

• Principle: Water molecules OH Bonds absorb specific near-infrared wavelengths (1.94 μm etc.) have strong absorption; the instrument emits multi-wavelength infrared light to irradiate the material and measures the reflected light intensity; usingDual / Three-wavelength compensationEliminates interference from material color and roughness, converting to moisture content.
• Features:Does not contact or damage the sample, millisecondsResults in seconds, can monitor continuously online。
• Disadvantages:Must be calibrated, different materials require establishing corresponding calibration models; affected by material thickness and surface conditions; can only measure moisture at a certain depth on the surface.

II. Instrument Classification

1. Benchtop infrared heating moisture analyzer: Laboratory, grains, feed, plastic pellets, medicinal materials, pastes; sampling for testing, sample is dried and destroyed.
2. Handheld near-infrared moisture meter: On-site rapid spot checks, non-destructive.
3. Online near-infrared moisture meter: Probe type on production lines, installed above the conveyor belt, real-time output 420mA/RS485 Signal, can be linked with drying equipment for closed-loop production control, for papermaking, tobacco, coal, food, building materials, chemical powders.

III. Main Industry Applications

• Grain and Feed: Cereals, flour, feed pellets
• Food and Tobacco: Tea, milk powder, tobacco shreds, baked goods
• Papermaking and Textiles: Paper, paperboard, textiles
• Building Materials and Chemicals: Coal powder, ores, fertilizers, various powders and granules
• Pharmaceuticals: Traditional Chinese medicine decoction pieces, granular materials

IV. Pros and Cons Comparison

Infrared heating (thermogravimetric)

✅Advantages: Simple principle, close to oven method, no complex modeling needed; low cost.❌Disadvantages: Slow testing; sample destruction; interference from volatile substances; can only sample for laboratory testing, not online.

Near-infrared spectroscopy type

✅Advantages:Non-destructive, extremely fast, can measure continuously online, sample can be retained and reused。 ❌Disadvantages: High procurement cost; each type of material needs calibration against the oven method; affected by surface, dust, and steam; measures surface moisture only.

V. Key Precautions

1. Calibration is the core: Near-infrared instruments must be calibrated using the oven method (national standard). Calibration must be redone when changing materials; universal curves have large errors.
2. Online probe: Avoid strong light, steam, and dust; clean the lens regularly; material thickness should be uniform, and the light spot should fully cover the material surface; install the probe at the height specified in the manual.
3. Heating type: Spread sample evenly with uniform thickness; heating chamber is at high temperature, beware of fire and burns; use caution with volatile and heat-sensitive samples.
4. Environment: Avoid direct strong light, large vibrations, and voltage fluctuations; allow sufficient warm-up after power-on before testing.