In-Situ Gas Analyzers

In-situ measurement demands a narrow matrix envelope to stay reliable in production: stable optical transmission, tolerable dust and droplet loading, and predictable long-term window-purge behavior. GESHINE deploys in-situ on the paths where those conditions consistently hold — combustion O₂ (paramagnetic direct-mount) and SCR/SNCR NH₃ slip (cross-duct TDLAS) — and deliberately routes acid gases, trace moisture, chlorine, and multi-component duty through extractive sampling, where heated conditioning and controlled dew point deliver calibration predictability and a tractable maintenance cadence. The two formats are complementary, not redundant: in-situ for fast control where the matrix permits, extractive for everything else. If you have an application outside the current in-situ scope and want an independent feasibility review, our application engineers can run one.

An in-situ gas analyzer mounts directly on the process duct or stack and measures gas concentration in the live stream without extracting a sample. A laser or light source is aimed across the duct from one flange to a receiver (or a retro-reflector) on the opposite side, and the beam interacts with the gas over the real duct cross-section. This eliminates sample transport lag, preserves reactive or condensable species, and removes an entire sample conditioning system from the analyzer scope.

In-situ is the right call when response time matters (combustion trim, safety interlocks, SCR/SNCR ammonia slip feedback), when the species is reactive or sticky and does not survive a heated sample line (HCl, HF, NH₃, H₂O), and when the process conditions are hot but relatively clean (modern gas-fired stacks, reformer outlets, clean flue gas). Extractive is the safer choice when the matrix is heavily laden with dust or droplets, when regulated protocols require sample conditioning and validation, or when multi-component speciation requires a bench-style analyzer that only runs on a conditioned sample.

Cross-duct TDLAS systems typically deliver T90 response under 1 second because there is no sample transport delay — the laser interrogates the gas as it flows past the probe optics. For control loops on combustion or scrubber dosing, this sub-second response is often what justifies the in-situ choice over a 15–60 second extractive loop that includes heated tubing, cooler, filter, and pump transit time.

Three constraints dominate. First, optical path stability: heavy dust, condensing moisture, or droplet formation reduces signal transmission and can trigger low-signal alarms. Second, duct geometry: the installation needs two opposing flanges at the right height and angle, with clear optical line of sight and tolerable alignment deflection from thermal expansion or vibration. Third, window fouling: corrosive or particulate-laden streams require purge-air window protection, and operators need to factor purge reliability into the long-term O&M plan.

In most cases no — the whole point is to remove the sample conditioning loop. What you typically still need is a small instrument-air supply for window purge, a local calibration interface for span and zero verification, and sometimes a validation cell for periodic cross-check. For hybrid installations where the in-situ beam covers the primary measurement and a secondary extractive loop handles calibration or backup, the ZS-SCS family can be co-specified alongside the analyzer.

Move to extractive when the duct is heavily loaded with dust or water droplets that cannot be reliably purged, when the measurement must be certified under a protocol that assumes sample conditioning (some US EPA performance specs, some EN standards for specific pollutants), when you need simultaneous multi-component analysis that only a conditioned-sample FTIR or GC-based analyzer can provide, or when the duct geometry simply does not permit opposing flanges. See the Extractive Gas Analyzers page for the sample-conditioned alternative.