Alphasense TH Series Digital Electrochemical Gas Transmitter Modules (CO, SO₂, H₂S, NO₂)

Overview

The Alphasense TH Series Digital Electrochemical Gas Transmitter Modules are compact, OEM-ready signal conditioning and interface units engineered for seamless integration with Alphasense’s industry-standard B-Series and A-Series electrochemical toxic gas sensors. Designed specifically for fixed-system applications in industrial hygiene, process safety, and environmental monitoring, these modules convert raw sensor output—generated via selective electrochemical oxidation or reduction reactions—into a robust, linearized 4–20 mA analog current signal. Each module is pre-calibrated and temperature-compensated to ensure high reproducibility across ambient operating conditions (–20 °C to +50 °C). Unlike generic signal conditioners, the TH Series incorporates proprietary low-noise analog front-end circuitry optimized for the microampere-level current outputs typical of electrochemical cells, minimizing drift and improving long-term stability. The modules operate on a wide unregulated DC supply (7.5–35 VDC), making them compatible with standard industrial power rails and simplifying system-level power architecture.

Key Features

• OEM-optimized design with minimal footprint (65 × 45 × 22 mm) and screw-terminal connectivity for rapid board-level or enclosure-based integration
• Factory-calibrated for specific Alphasense sensor types (THCO for CO-B4, THSO₂ for SO₂-B4, THH₂S for H₂S-B4, THNO₂ for NO₂-B4), eliminating need for end-user calibration setup
• Integrated cold-junction compensation and digital temperature correction using onboard thermistor, ensuring ±2% full-scale accuracy over –20 °C to +50 °C
• Galvanically isolated 4–20 mA output compliant with NAMUR NE43 fault signaling standards (20.5 mA = sensor saturation, 3.6 mA = fault/under-range)
• Reverse-polarity and overvoltage protection (up to 40 VDC transient) to safeguard against field wiring errors and ESD events
• RoHS-compliant PCB assembly with conformal coating option (TH Series-C variant) for enhanced humidity and chemical resistance in harsh industrial enclosures

Sample Compatibility & Compliance

The TH Series modules are exclusively validated for use with Alphasense’s certified electrochemical sensors—including the B4 and A4 families—for carbon monoxide (CO), sulfur dioxide (SO₂), hydrogen sulfide (H₂S), and nitrogen dioxide (NO₂). Each module is paired with its corresponding sensor during manufacturing and tested per IEC 60079-29-1 (explosive atmospheres – gas detectors) and EN 45544-1 (workplace exposure – electrochemical gas detectors). While the modules themselves are not intrinsically safe, they are routinely deployed in Zone 2/Class I, Division 2 systems when installed behind approved safety barriers (e.g., Zener or galvanic isolators). All units meet CE marking requirements under the Electromagnetic Compatibility Directive (2014/30/EU) and the Restriction of Hazardous Substances Directive (2011/65/EU). Documentation packages include traceable calibration certificates and sensor-specific response time data (T₉₀ < 30 s for most configurations).

Software & Data Management

As analog-output-only modules, the TH Series does not incorporate embedded firmware, USB interfaces, or wireless telemetry. However, their standardized 4–20 mA output ensures plug-and-play compatibility with programmable logic controllers (PLCs), distributed control systems (DCS), and SCADA platforms widely used in petrochemical, wastewater, and semiconductor facilities. When integrated into larger safety instrumented systems (SIS), the modules support audit-trail-capable data logging when connected to controllers compliant with IEC 61511 and ISA-84. For system integrators requiring diagnostics, optional external loop testers (e.g., Fluke 789 or Beamex MC6) can verify live zero/span, sensor health, and linearity without interrupting operation. Configuration parameters—including zero offset and span gain—are set at manufacture and are non-field-adjustable, aligning with SIL-2 functional safety principles for unattended fixed-gas monitoring.

Applications

These transmitter modules serve as the foundational signal interface in fixed toxic gas detection systems deployed across multiple regulated sectors. Typical use cases include continuous monitoring of CO in boiler rooms and parking garages (per EN 50545-1), SO₂ leak detection in sulfuric acid production lines, H₂S surveillance in biogas upgrading stations and oil & gas refineries (in accordance with OSHA 1910.120 and API RP 14C), and NO₂ exposure tracking near diesel generator enclosures or tunnel ventilation shafts. Their cost-effective, drop-in integration capability makes them especially suitable for Tier-2 equipment manufacturers developing UL/CSA-certified gas panels or OEMs building multi-sensor air quality analyzers for smart city infrastructure.

FAQ

Can the TH Series modules be used with non-Alphasense electrochemical sensors?
No. The TH modules are calibrated and compensated specifically for Alphasense B-Series and A-Series sensor characteristics, including baseline current, sensitivity slope, and temperature coefficient profiles. Interchangeability with third-party sensors is not supported.
Is field recalibration possible?
No. The modules are factory-calibrated and contain no user-accessible trim pots or digital configuration interfaces. Recalibration requires return to an Alphasense-authorized service center or replacement with a newly calibrated unit.
What is the recommended cable length between sensor and module?
For optimal signal integrity, Alphasense recommends keeping the sensor-to-module connection ≤ 1 meter using twisted-pair shielded cable. Longer runs require evaluation of voltage drop and noise coupling, particularly in electrically noisy environments.
Do TH modules comply with FDA 21 CFR Part 11 or GMP requirements?
No—these are hardware signal interfaces, not standalone analytical instruments. Compliance with Part 11 or GMP applies to software-controlled data acquisition systems, not analog transmitters. However, they may form part of a validated system when integrated into a compliant DCS or SIS architecture.
Are explosion-proof housings available from Alphasense?
Alphasense supplies only the bare PCB module. Enclosure selection—including flameproof (Ex d), increased safety (Ex e), or intrinsic safety (Ex i) variants—is the responsibility of the system integrator and must follow local hazardous area classification and certification requirements.