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For checking purity of hydrogen (H2) in H2-cooled generators and synchronous converters. The Model 381 Series will also monitor the safe purging of H2 during shutdown or startup. This model is designed specifically for generators that are purged with nitrogen (N2) instead of carbon dioxide (CO2).

The Nova 381 Series Tri-Gas Analyzer is designed for monitoring the H2 purity inside a power generator and to monitor the purging procedure during a generator shutdown or startup. This analyzer is specifically for generators that are purged with N2 instead of the more commonly-used CO2. The analyzer contains a temperature compensated thermal conductivity (T/C) cell, electochemical O2 sensor, amplifier board, digital readout, range switch, pressure regulator, gas flow control valve, pump and a flow indicator. A 4-20mA recorder output is standard.

The T/C cell does not burn the sample nor is it consumed in any way, so it has a life expectancy of over 10 years. The electrochemical O2 sensor typically has 3-5 year life and is easy and inexpensive to replace. Measurement results are fast and accurate. A rechargeable 'gel cell' battery provides enough power for about 4-6 hours of continuous operation and the analyzer can be used while it is being recharged.

Unit of Measure


Method of Detection

N/A Thermal conductivity (T/C) cell, electrochemical O2 sensor

Ranges Available

N/A Range 1: 0-100% H2 in Air
Range 2: 0-100% H2 in N2
Range 3: 0-100% Air in N2


N/A 0.1% of gas measured

Accuracy & Repeatability

N/A ±1% F.S except in 85-100% H2 in Air range, which is within 0.5% absolute H2


N/A H2 in N2 or Air in N2, ± 2% F.S. per week maximum drift; 0-100% H2 in Air range is ± 0.4% per week maximum

Response Time (T-90)

N/A 10-15 seconds to 90% step change - not including sample transport time

Ambient Temperature Range

N/A 0 to 50 ºC32 to 120 ºF


N/A ± 1.0% of F.S. on H2 in Air range. ± 2% of F.S. in H2 or Air in N2 ranges

Size & Weight

N/A 9 1/2" L x 7" W x 6 1/2" H @ 12 lbs (24 x 17 x 18 cm @ 3.6 kg)


N/A AC/DC Operation. 115 VAC, 60 Hz for recharging (220 VAC, 50 Hz available)

Output Options

N/A 4-20 mA or 0-1 VDC

Hazardous Area Rating Options

N/A General Purpose, Non-Hazardous


N/A For checking purity of hydrogen (H2) in H2-cooled generators and synchronous converters.



  • Rugged design that is easy to operate
  • Fast warm up and response
  • Monitors 0-100% H2 in air, 0-100% H2 in CO2, 0-100% Air in CO2
  • Rugged long life thermal conductivity cell
  • Digital readout meter with backlight
  • Rechargeable battery operation
  • Modular layout that is easy to maintain
  • Built in flow meter, flow control valve and pump
  • Built in pressure regulator prevents over pressuring of pump and sensor
  • Weatherproof (WP) cabinet with clear lexan cover
  • Sample pressure ranges 0.5 PSI to 125 PSI



  • Recorder outputs of 0-1 V or 4-20 mA
  • Suitcase (K) style cabinet available

Unique Applications


    All Nova analyzers are built using proven technologies and techniques. If this product does not suit your application, please contact Nova. In many cases, we are able to build an analyzer specific to your needs.

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