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Item # Model 425N4, Continuous Process Analyzer for Binary Gas Mixtures by Thermal Conductivity, Wall Mounted NEMA4 (IP65) Enclosure Rating

The Nova 425 Thermal conductivity (TC) Analyzer has many applications in industry where the measurement of one gas in a two gas or some multi-gas mixtures is required. The Nova TC cell is temperature controlled and its high stability enables it to be used even in high purity measurements. Since the TC cell does not consume the sample, have any moving parts, hot wires, or sealed chemicals, it will last for many years.
In operation, the TC cell detects the rate at which the sample gas conducts heat away from a Resistance Temperature Device (RTD) with reference to a similar RTD surrounded by air (or other reference gas). A sample gas containing the gas to be measured will cause the temperature, and its resistance, to change with respect to the reference RTD. This will cause an output from the Wheatstone bridge measuring circuit which is calibrated and displayed on a digital meter.

Cabinet: NEMA 4 Weather-proof steel cabinet with window

Specifications  · Applications  · Features  · Options  · Calibration  · Unique Applications


Method of Detection

CH4 in N2, air, or CO2; SF6 in CO2, etc.
CO2 in N2, H2, air, Ar, O2, He, etc

O2 in Ar, CO2, He, H2, etc

RTD-based TC cell can be used to measure almost any binary gas mixture such as H2 in N2, O2, air, SO2, Ar, He, NH3, etc

Ranges Available

0-2% to 0-100% and suppressed ranges such as 95-100%


0.1% of gas to be measured

Accuracy & Repeatability

±1% of full scale


Less than 1% of full scale per month

Response Time (T-90)

10-15 seconds to 90% step change

Ambient Temperature Range

32 to 122°F (0 to 50°C), Lower temperatures (-5°F, -20°C) with Cold Weather Package


±1% of full scale

Size & Weight

Dimensions will vary depending on enclosure style and options required


115 VAC, 60 Hz
220 VAC, 50 Hz

Output Options

4-20 mA into 500 ohms non-isolated standard
Isolated 4-20 mA, RS232, RS485, MODBUS, Ethernet outputs


High and/or low alarm contacts available, relay contacts SPDT 5A @ 220 VAC rating
Low flow alarm

Analyzer Type

Binary Gas Analyzer

Hazardous Area Rating Options

General Purpose, Non-Hazardous

    For continuous analysis of many binary gas mixtures comprised of H2, CO2, O2, CH4, SO2, Ar, He, NH3, SF6, air, and others. Applications include heat treating atmospheres, welding gas mixtures, blanketing gas mixtures, ammonia synthesis, leak detection, purge monitoring, flue gas, magnesium blanketing by SF6 and others.

  • Bright digital readout
  • Lower cost than infrared, GC or mass spectrometer
  • High stability, microprocessor-controlled, long-life thermal conductivity (TC) cell
  • Easy-to-maintain modular layout
  • Built in sample pump or pressure regulator
  • 4-20 mA outputs
  • Sensors mounted in temperature controlled heated box to improve accuracy

  • Hi/Low gas, low flow, and diagnostic alarms available
  • Isolated analog, RS232, RS485, MODBUS, and Ethernet outputs available
  • Sample conditioning systems available for removal of moisture, acidic gas, and dust
  • Cabinet purge system available for use in hazardous areas
  • One-step 'cal-now' button calibration with touch screen LCD display
  • Full automatic calibration with touch screen LCD display
  • Cold weather package for operation to -5°F (-20°C)
  • Cabinet coolers can be fitted to most models

  • Air or nitrogen for zero
  • Analyzed calibration gas for span

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.


·  Application process


425 Process TC Analyzer
(PDF, 583KB)