Valmet LEV‑EL PG4 N1 – Hydrogen Sulfide (H2S) Sensor (600 mbar)

The Valmet LEV‑EL PG4 N1 is a high‑performance electrochemical sensor specifically designed for the detection of hydrogen sulfide (H2S) gas in industrial environments. With a measurement range of 0 to 600 mbar (0 to 60 kPa), this sensor is suitable for safety monitoring, process control, and environmental compliance applications. The PG4 N1 variant is optimized for fast response, long life, and stable operation in harsh conditions, making it ideal for use in pulp and paper mills, wastewater treatment plants, and chemical processing facilities.

Electrochemical Sensing Principle

The sensor operates on the principle of electrochemical oxidation of H2S at a working electrode. The gas diffuses through a hydrophobic membrane into the electrolyte, generating a current proportional to the gas concentration. The sensor includes a three‑electrode configuration (working, counter, and reference) for precise potential control, minimizing drift and interference from other gases. The output signal is a linear current (or voltage) that is temperature‑compensated by an onboard thermistor.

Measurement Range and Accuracy

The calibrated range is 0 to 600 mbar H2S, with a resolution of 0.5 mbar. Accuracy is ±2 % of full scale at 25 °C, with a repeatability of ±1 %. The response time (T90) is less than 15 seconds, allowing rapid detection of gas leaks. The sensor exhibits minimal cross‑sensitivity to common interfering gases such as CO, SO2, and NO, ensuring reliable readings in mixed gas atmospheres. The long‑term drift is less than 2 % per year.

Output Signal and Electrical Interface

The PG4 N1 provides a 4‑20 mA current loop output (two‑wire) that is linearly proportional to the H2S concentration, with a loop supply voltage of 12‑36 V DC. It also includes a digital Modbus RTU interface (RS‑485) for advanced communication and diagnostic data access. The electrical connection is made via a 6‑pin military‑grade connector or screw terminals. The sensor is powered by the loop and consumes less than 500 mW.

Mechanical Design and Environmental Protection

The sensor is housed in a rugged 316L stainless steel enclosure with a sintered PTFE filter that protects the sensing element from dust and aerosols. The housing is rated IP66/67 for protection against water ingress and dust. The sensor mounts via a 3/4‑inch NPT thread, allowing direct installation into process pipelines or ducting. The dimensions are 120 mm (length) x 40 mm (diameter), and it weighs approximately 0.4 kg.

Temperature and Operating Conditions

Operating temperature range is ‑20 °C to +50 °C; relative humidity is 15‑90 % non‑condensing. The sensor includes automatic temperature compensation to maintain accuracy across the entire range. The pressure range is 800‑1200 mbar absolute, with a maximum overpressure of 2 bar. The sensor is suitable for use in non‑hazardous areas (standard version) and is available in intrinsically safe (Ex ia) versions.

Calibration and Maintenance

Calibration is performed using a certified H2S gas mixture. The sensor supports zero and span calibration via the Modbus interface or through the analog loop using a calibration adapter. A calibration interval of 12 months is recommended. The sensor has an expected operational life of 2‑3 years in clean environments, with the electrolyte and electrodes being factory‑sealed and non‑serviceable. Replace the entire sensor at end of life.

Applications

This sensor is used for H2S monitoring in pulp mill digesters, black liquor tanks, paper machine hoods, and sewer networks. It is also used for personal safety in confined spaces and for environmental stack gas monitoring.

Installation and Commissioning

Mount the sensor in a location with adequate gas flow. Connect the 4‑20 mA or Modbus wiring to the controller. Apply power and allow 30 minutes for stabilization. Perform a zero calibration in fresh air and a span calibration with a known gas concentration. Verify the output against a portable gas detector.

Safety and Certifications

The sensor complies with EN 45544‑1 for toxic gas detection and is CE marked. The intrinsically safe version (optional) is ATEX certified for Zone 1 and Zone 2 hazardous areas.

Conclusion

The Valmet LEV‑EL PG4 N1 H2S sensor (600 mbar) provides accurate, reliable detection of hydrogen sulfide for process safety and environmental monitoring. Its robust construction and low maintenance make it a trusted choice for industrial gas detection.