1738 Dew Point Transmitter

1738 Dew Point Transmitter

Providing in-situ measurement of Oxygen and Dew Point in annealing and holding furnaces with protective atmospheres of hydrogen and nitrogen (H2Nx).

The Novatech 1738 Dew Point Transmitter continuously monitors the dew point of annealing furnaces allowing operators to take corrective action to prevent expensive re-work due to oxidation or decarburization.


Measure Oxygen During Furnace Purge Cycle

The 1738 Dew Point Transmitter uses an platinum zirconia sensor capable of accurately measuring oxygen concentration in the range of 100% down to 1 x 10-30%.  This oxygen level can be re-transmitted back to a furnace controller via a scaled 4-20mA analog output, or relay contact to indicate the oxygen is below a set threshold.

Real-time Quality Control during the Annealing Process

During the annealing process the same in-situ probe is used to continuously monitor the dew point temperature inside the furnace.

Additionally this transmitter calculates the pre-reactive oxygen concentration in the atmosphere derived from the remaining oxygen after reacting with the hydrogen present in a state of equilibrium.  This measurement is used to detect leaks that may result in dangerous levels of oxygen in the furnace.

Key Features at a Glance

  • Set the hydrogen content inside the furnace using the keypad.
  • Two fully programmable isolated 4-20mA outputs for re-transmitting up to two process variables including oxygen, dew point and pre-reactive oxygen.
  • Four programmable alarm output relays
  • Built in digital Modbus™ communications
  • Very low maintenance and re-calibration

Dual sensors provides redundancy to prevent costly shutdowns if a probe failure occurs

The Novatech 1738 Dew Point Transmitter can control with two separate in-situ probes providing options for multiple readings, averaging and redundancy protection.  Having two probes simultaneously measuring dew point can prevent costly shutdowns in the event of a single probe failure.

The Novatech 1738 tells you what’s happening

All process related information and alerts can be viewed on the local display, as well as being re-transmitted using a range of fully programmable analog outputs, voltage free alarm relays or Modbus™ digital serial communications.

Operators are alerted to any failures or process related alarms with descriptive messages on the transmitter’s local display.  Alarms can also be used to trigger internal relays that can be wired to external indicator lamps and buzzers and alarm states can also be monitored via digital communications.


  • One or two zirconia oxygen probes or sensors
  • One zirconia sensor & auxiliary thermocouple type J, K, R or S
  • Burner “On” signal (dry contact)
  • Purge air flow switch


  • Four programmable alarm relays
  • Two isolated 4-20mA or 0-20mA
  • SSR outputs to purge & calibration check gas solenoid valve

Range of Outputs

  • Dew Point: -60 to 40°C
  • Average Dew Point: -60 to 40°C
  • Linear Oxygen: 0 to 100%
  • Avg Linear Oxygen: 0 to 100%
  • Reducing Oxygen: 10-30 to 102%
  • Avg Reducing Oxygen: 10-30 to 102%
  • Pre-Reactive Oxygen: 0 to 10%
  • Avg Pre-Reactive Oxygen: 0 to 10%
  • Probe EMF: 0 to 1300mV
  • Aux TC Temperature: 0 to 1400°C


  • Common alarm relay with 20 user selectable instrument alarm functions.
  • Three programmable process alarm relays for
    • Oxygen High
    • Oxygen Deviation
    • Dew Point High
    • Dew Point Deviation
    • Pre-Reactive Oxygen High (two separate thresholds)
    • Probe Temperature Low
    • Cal. Check in Progress
    • Purge in Progress
    • Any alarm condition not selected for the common alarm
  • Multiple selections can be made for all relays

Alarm Contacts

  • Normally open failsafe (open for alarm state)
  • 250VAC / 30VDC, 2A

Range of Local Indication

  • 1.0 x 10-30% to 100% Oxygen
  • 0.01ppm to 10,000ppm – automatically defaults to exponential format below 0.01ppm and percent format above 10,000ppm (1%)

Network Interface

  • RS-485 MODBUS™

Secondary Parameter Display

  • Probe 1/2 Dew Point
  • Average Dew Point
  • Probe 1/2 TC Temperature
  • Probe 1/2 EMF
  • Probe 1/2 Impedance
  • Probe 1/2 Oxygen %
  • Average Oxygen %
  • Probe 1/2 Pre-Reactive O₂
  • Average Pre-Reactive O₂
  • Auxiliary TC Temperature
  • Ambient Temperature
  • Ambient RH%
  • Runtime
  • Service Date
  • 4-20mA Output 1
  • 4-20mA Output 2

Probe 2 & Average Parameters only available with two probes


  • ± 1% of the actual oxygen reading with a repeatability of 0.5%. For example, at 2% oxygen the accuracy would be ±0.02% oxygen.

Environmental Rating

  • Operating Temperature -25°C to 55°C
  • Relative Humidity 5% to 95% (non-condensing)
  • Altitude 2000m Maximum

Power Requirements

  • Mains Voltage 100 to 240VAC -6/+10%, 50/60Hz
  • Overvoltage Category II (IEC60364-4-443)
  • Requires 5W for controller plus probe power

Degree of Protection

  • IP65
  • IP54 with internal reference air pump


  • 315mm W x 190mm H x 110mm D


  • 3.3kg (7.3lb)
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