Use the comparison to eliminate the wrong route
A technology comparison is useful when it reduces an engineering risk. It is not useful when it turns three different measurement principles into a list of marketing adjectives.
Start with the installation: a low-range diffusion sensor mounted near a pipe is not automatically a controlled flow-through measurement. An extractive analyzer with a pump is not automatically interchangeable with a direct insertion module.
What changes for the host instrument
| Decision question | TDLAS | NDIR | Catalytic |
|---|---|---|---|
| Measurement basis | Narrow laser absorption line with optical path and signal processing. | Broadband infrared absorption with filter and detector conditions. | Catalytic combustion reaction that depends on the required operating conditions. |
| High CH₄ range | Configuration-dependent; Line B is being developed around a 0–100 %vol target range. | Can appear in published drainage instruments; the actual cell, compensation and evidence must be checked. | Primarily associated with low-range combustible-gas detection; it is not assumed to be the high-range drainage route. |
| Oxygen / background | Not based on combustion, but background gas and cross-interference still need review. | Not based on combustion; optical and gas-cell conditions still matter. | Requires oxygen and has a different safety and maintenance logic. |
| Gas path | Extractive or flow-through path must be defined. | Cell, conditioning and compensation remain part of the system. | Diffusion and environmental conditions strongly affect response. |
| Evidence question | Line, path, range, pressure, temperature and calibration conditions. | Cell, pressure compensation, oxygen/background and host data. | Oxygen, poisoning, environmental exposure, calibration and safety behaviour. |
The honest decision rule
- Choose the gas path first. Decide whether the gas is diffusing, pumped through a sample line or flowing through a window in the pipe.
- Then choose the concentration and pressure envelope. A published range without those conditions is not a complete selection input.
- Then check the host instrument file. The module must fit the enclosure or pipe, communicate with the controller and supply the evidence your approval route needs.
This comparison is not a claim that TDLAS is always better. Use it to compare each route against the work your host system must perform.
FAQ
Questions engineers ask next
Is TDLAS always the better choice than NDIR?
No. The right choice depends on gas path, range, pressure, temperature, maintenance, host integration and available evidence.
Can a low-range catalytic or environmental sensor be used in a drainage pipeline?
Not automatically. High concentration, negative pressure, gas composition, oxygen conditions and flow-through mechanics must be assessed for the actual installation.
Does a pipeline mounting position prove flow-through measurement?
No. A sensor can be mounted near or in a pipe while still relying on diffusion. The controlled gas path and pressure behaviour must be demonstrated separately.
What should be compared before the sensor principle?
Compare the measurement point, gas path, concentration band, absolute pressure, temperature, interface, maintenance and host-instrument evidence.