Introduction
Infrared filters look simple, like flat glass pieces. But in gas analyzers, they’re the silent gatekeepers that decide which light makes it through and which is cut off. The accuracy of CO₂ detection in a greenhouse, or methane monitoring near a petrochemical site, depends on that decision.
At Bodian, we’ve seen how different industries ask for very different things from their analyzers. A medical device maker might want compact filters with extreme wavelength precision. An oilfield client, on the other hand, needs filters that keep working in 60 °C heat with dust and hydrocarbons floating around. That’s where customization becomes more than a buzzword—it’s the only way to get reliable data day after day.
Fundamentals of IR Filtering in Gas Analyzers
Every NDIR (non-dispersive infrared) gas analyzer has the same skeleton: a source, a chamber, a filter, and a detector. The gas molecules in the chamber absorb very specific IR wavelengths. The filter makes sure the detector only sees that slice of light.
- CO₂ → 4.26 µm
- CH₄ (Methane) → 3.31 µm
- Propane / Butane → around 3.35 µm
Miss that absorption line, and the analyzer will never be trustworthy. Hit it exactly, and the system can track ppm-level changes. That’s why Bodian’s engineers spend so much effort on fine-tuning filter coatings, sometimes adjusting deposition times by just a few seconds to lock in the correct band.
Key Considerations in Customizing IR Filters
Wavelength Matching and Bandwidth Precision
Think of it as tuning a radio. If you’re slightly off the station frequency, you hear static. Same with filters—slightly off from the gas absorption line, and your analyzer starts “hearing” noise from other gases. For example, water vapor has broad absorption features. Without sharp edges, your CO detector will drift whenever humidity changes.
Our R&D team often makes narrowband filters with <6% full-width half-maximum. It sounds technical, but in real terms, it means a factory safety sensor can tell the difference between a harmless puff of steam and an actual CO leak.
Filter Material Durability and Environmental Resistance
Material choice matters. Glass works in labs, but try running it inside a cement plant and it will cloud up in weeks. That’s why Bodian offers substrates like germanium and silicon, coated with hard, environmentally resistant layers.
One client running continuous emission monitoring near the Bohai coast installed our filters three years ago. They face salt spray, strong winds, and temperature swings from –20 to +40 °C. The filters are still above 90% transmittance today. That’s durability tested by nature, not just by spec sheets.
Integration Compatibility
Another overlooked point is mechanical fit. If the filter isn’t flat enough, or doesn’t match the detector aperture, calibration drifts. Some of our analyzer OEM customers ask for square filters as small as 3×3 mm because their modules are ultra-compact. Others need round 25 mm filters with exact thickness control so their rotating filter wheels don’t wobble.
Because Bodian operates both R&D labs and volume production lines, we can meet these odd requests without clients waiting six months for tooling.
Customization of IR Emitters and Filters
IR Emitter Customization for Harsh Environments
In high-dust environments like steel plants, IR lamps degrade fast. That’s why we sometimes supply sealed emitters with sapphire windows, paired with filters tuned for hydrocarbon bands. When both sides—the source and the filter—are ruggedized, analyzers can run continuously for years without replacement.
Filter Selection Techniques
Different applications need different filter types:
Narrowband filters with high optical density blocking for refrigerant leak detection.
Broader bandpass filters for industrial combustion analyzers measuring mixed hydrocarbons.
Material and Coating Options
Bodian’s coating workshops in Beijing run both Leybold and Optorun machines. This allows us to deposit precise dielectric multilayers with very steep slopes. Customers benefit from cleaner separation between passband and stopband—a crucial factor when trying to measure gases like SF₆ at trace levels.
Trade-offs in Production
Customization also has a practical side: cost and lead time. For a research lab ordering 10 pieces, we might deliver ultra-narrow filters with exotic substrates. For an OEM ordering 20,000 pieces, we’ll recommend designs that balance spectral precision with stable mass production. Clients appreciate hearing the trade-offs clearly, instead of finding out later during scaling.
System Design and Calibration Best Practices
Assembling the Detection Path
Filters don’t work in isolation. The way light enters them—at 0° or 5°—shifts the passband. That’s why we tell clients to keep mounting tolerances under ±1°. In our own lab, we’ve rotated filters during testing and watched a 4.26 µm filter drift by 0.03 µm just from a few degrees tilt.
Calibration Protocols
Even the best filter needs calibration support. In automotive exhaust analyzers, a nitrogen zero-gas and a certified span gas are used every six months. With stable coatings, drift stays small, but calibration makes the analyzer credible in regulated industries.
Maintenance and Troubleshooting Tips
A funny but true fact: many “filter failures” reported to us turned out to be fingerprints. Oils from handling absorb IR and cut transmission. It’s why we remind technicians—always use gloves, always store in clean cases. It’s basic, but ignoring it costs downtime.
Application Examples and Case Scenarios
Standard Lab Setup
A European university lab ordered a batch of Bodian CO₂ filters—4.26 µm center, 90% peak transmission. Their climate research analyzer needed stability over a year-long run. After 12 months, their data showed <1% drift.
Industrial Harsh Environment
In a Northern China refinery, analyzers faced temperatures above 180 °C. We supplied germanium filters with AR coatings stable up to 200 °C. The filters outlasted two generations of detectors—something even the engineers on-site didn’t expect.
Multi-Gas Detection
Portable air quality monitors often need CO₂, CH₄, and CO detection. Bodian delivered matched filter sets, each precisely centered, so the analyzer could swap filters without introducing bias. That consistency is what made their product win a tender for municipal monitoring projects.
Conclusion
Customizing IR filters isn’t about adding fancy features. It’s about making analyzers dependable—whether they’re in a clean hospital room or a dusty refinery. Bodian’s strength lies in bridging R&D precision with scaled manufacturing. That’s why clients from environmental monitoring, industrial process control, and even beauty device makers come to us: they know we can deliver filters that fit their environment, not just a generic spec.
If you’re designing a gas analyzer, the filter deserves more than a line item in the BOM. It’s the heart of the measurement chain.
Looking for IR filters built for your exact gas analyzer needs? Talk to Bodian’s optical experts today and start your custom project with confidence.
FAQs
Q1: What’s the most common mistake when customizing IR filters?
A: Ignoring cross-interference. Water vapor is everywhere, and without sharp filter cut-offs, humidity can skew CO or CO₂ readings badly.
Q2: How long do Bodian’s custom filters last?
A: In lab conditions, over 10 years. In harsher outdoor use, 3–5 years is typical, thanks to hard coatings and rugged substrates.
Q3: Can Bodian deliver both small prototypes and mass production?
A: Yes. We often start with 10–20 prototype filters for testing. Once designs are approved, our production line scales up to tens of thousands with consistent performance.
Beijing Bodian Optical Tech. Co., Ltd.
