ZS6300-H2 Process Hydrogen Analyzer

TCD reads the Wheatstone-bridge imbalance created when H2 replaces the reference matrix in the sample cell. H2 has roughly 7× the thermal conductivity of air, so the signal is strong and linear from a few percent up to 100 %vol — the bulk-purity window this SKU is sized for. At the low end, thin-film element drift, self-heating stability and reference-cell matching set a practical noise floor around 100 ppm; forcing a TCD below that erodes repeatability rather than revealing real signal. Trace ppm / ppb duty therefore belongs to physically trace-capable hardware — EC, pulsed-discharge helium-ionisation, or GC with a dedicated TCD channel — and stays outside the scope of this SKU.

Cathode cell-gas is mostly H2 with residual O2, N2 and traces of Cl2 crossing through the membrane. TCD is a physical-property measurement that does not discriminate by chemistry, so any gas whose thermal conductivity differs from the reference matrix biases the bridge — O2 and N2 are close enough to the dry-air reference to be absorbed into the matrix calibration, while Cl2 (roughly one-third the thermal conductivity of air) must be held within the engineered matrix window confirmed at order. Upstream conditioning (ZS-SCS-600 cool-dry plus a dedicated Cl2 knock-out) removes wet Cl2 before the sample cell, and the factory configures the reference-cell charge and matrix compensation against the customer-declared cell-gas composition. Accuracy is specified against that declared matrix, not against arbitrary mixtures.

Yes for continuous purity monitoring, and no for CO2-H2 scavenging. In service the generator runs 97–99 %vol H2 with alarm bands around 95 %vol, and the 0–100 %vol range resolves that window comfortably. During scavenging, start-up and stator purges the internal gas passes through 0–30 %vol CO2 / air / H2 mixtures, where the multi-range firmware switches to the 0–10 %vol or 0–25 %vol range without optics change. IEEE C50.13 / ASTM D7968-style plant purity procedures, seal-oil water content and cooler-integrity tests are application-side workflows — the ZS6300-H2 delivers the H2 %vol input to those procedures, it does not replace them.

No. ISO 14687-2 Grade D defines fuel-cell-grade H2 with mandatory limits on multiple trace impurities — CO at 0.2 ppm, total sulphur at 0.004 ppm, NH3 at 0.1 ppm, total halogens at 0.05 ppm, plus moisture, THC and inert gases. That is a trace-impurity audit, not a bulk-purity measurement, and it cannot be performed on a TCD whose detection floor sits around 100 ppm H2. Fuel-cell-grade audits require lab-grade EC, pulsed-discharge helium-ionisation or GC-based hardware with traceable impurity standards. This duty is retained as a Conditional engineering-review path and is explicitly not claimed on the ZS6300-H2 data sheet.

The two duties share the word “hydrogen” but address different workflows. The ZS6300-H2 is a Process-purity bulk %vol analyzer that sits on a cell-gas header, reformer outlet or generator loop, feeds %vol to the DCS, and does not participate in the Fire & Gas layer. Fixed and portable %LEL hydrogen leak detectors are Safety instruments — catalytic-bead / EC sensors calibrated in %LEL for area monitoring, leak alarm and confined-space entry, anchored in IEC 60079 / ATEX F&G logic. A plant commonly runs both: the Process analyzer reports purity for yield, the Safety detectors report alarm state for personnel protection. Do not swap roles — the ZS6300-H2 is not a leak detector, and %LEL Safety detectors are not process-purity instruments.