Prothermo NMT539 Average Temperature Converter

Prothermo NMT539 Average Temperature Converter

The Prothermo NMT539 provides a single, intrinsically safe solution for average temperature and water bottom (interface) measurement. Choose the modules you need – temperature probe, water bottom sensor, converter – or combine them together into a single new instrument.


  • Overview
  • Specifications
  • Options
  • Resources
  • Related Products

Meets API Standards

The Prothermo NMT539 is installed vertically onto spheres, bullets, cone, dome or floating roof tanks. Measurements are based on API (American Petroleum Institute) Manual of Petroleum Measurement Standard, Chapter 7. It is ideal for high accuracy or custody transfer applications.



Liquid and Vapor Profiles

The Prothermo NMT539 can contain up to 16 temperature elements. A continuous measurement profile of average liquid and/or average vapor temperature throughout the tank is available by reading the position and temperature of each element.




Water Bottom Sensor

The Prothermo NMT539 can determine the interface between water and petroleum products in the bottom 3 or 6 ft (1 or 2 m) of a tank. Temperature (Pt 100) elements can be set inside of the water bottom sensor so that water bottom functionality does not affect overall temperature measurement.



Tank Gauging System

Power and local HART communications are provided over a 2-wire, intrinsically safe (i.s.) connection from compatible instruments, such as servo gauges or monitors, and the 4590 Tank Side Monitor (TSM).





Converter Compatibility: Pt100, Cu100, Cu90, PtCu100, JPt100 (maximum 16 elements)
With probe: up to 16 Platinum (Pt. 100), Class A elements per IEC PUB 751 1995


Temperature Accuracy: ±0.15 °C (±0.27 °F), or better conversion accuracy based on IEC 60751 class A standard
Water Bottom: 4mm (±2mm) or better accuracy (at reference condition)

Measuring Range

Temperature probe:
‐40…+100 °C (‐40…+212 °F), ‐55…+235 °C (‐67…+455 °F), -170… +60 °C (‐328…+158 °F)
Water bottom probe: 0 to +100 °C (‐32 to +212 °F)

Power & Communications

DC16‐30V input (DC24V ±10% is supplied by the HOST i.s. HART communication line for standard applications.)
The Prothermo NMT539 consumes an average fixed current of 6 to 12 mA depending on configuration.


Factory Mutual (FM) ‐ Intrinsically Safe ‐ Class I, Division 1, Groups C/D
Contact Varec for ATEX and IECEx approved devices.
Housing: rated IP65 (open housing: IP20)
Probe: rated IP68

For complete technical specifications, download the technical document or product manual.

01 Approvals
  • FM ‐ Intrinsically Safe ‐ Class I, Division 1, Groups C & D
  • Contact Varec for ATEX and IECEx approved devices
02 Functionality
  • Converter
  • Temperature and Converter
  • Water Bottom and Converter
  • Temperature, Water Bottom and Converter
03 Temperature Measuring Range
  • 40…+100 °C (‐40…+212 °F)
  • ‐55…+235 °C (‐67…+455 °F)
  • ‐170… +60 °C (‐328…+158 °F)
04 Water Bottom Measuring Range
  • None
  • 1 m (3.3 ft)
  • 2 m (6.6 ft)
05 Cable Entry
  • Thread NPT 1/2
  • Thread M20
06 Process Connection
  • Flange JIS 10K 50A RF, Stainless steel 316
  • Flange ANSI 2″ 150lbs RF, Stainless steel 316
  • Flange DIN DN50 PN10 RF, Stainless steel 316
  • Flange JPI 2″ 150lbs RF, Stainless steel 316
  • Universal coupling, PF(NPS)3/4, (converter only)
  • Thread M20 (converter only)
07 Number of Elements
  • 2…Pt100 elements
  • 3…Pt100 elements
  • 4…Pt100 elements
  • 5…Pt100 elements
  • 6…Pt100 elements
  • 7…Pt100 elements
  • 8…Pt100 elements
  • 9…Pt100 elements
  • 10…Pt100 elements
  • 11…Pt100 elements
  • 12…Pt100 elements
  • 13…Pt100 elements
  • 14…Pt100 elements
  • 15…Pt100 elements
  • 16…Pt100 elements
08 Element Spacing
  • 2m (2000mm or 79″)
  • 1.5m (1500mm or 59″)
  • 1m (1000mm or 39″)
  • Custom element position & spacing
  • 3m (3000mm or 118″)
09 Probe Length
  • Probe length 3 ft to 131ft below flange to edge of probe
  • … probe length
  • … probe length, gas‐tight feed through
10 Mounting Accessories
  • Anchor weight 7.09″ tall, diameter 4.72″ (180mm tall, diameter 120mm)
  • Anchor weight – Low profile to be laid on bottom of tank Length 39.37″ (1000mm); Diameter 1.61″ (41mm)
  • Tensioning wire + top anchor
  • Tensioning wire, wire hook, R1 top anchor


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Application Checklists

Temperature Tank Gauging Checklist
Checklist for Temperature Tank Gauging needs.
Radar Tank Gauging Checklist
Checklist for Radar Tank Gauging needs.

Parts and Accessories

Servo Tank Gauging Checklist
Checklist for Servo Tank Gauge needs.
NMT539 Average Temp Water Bottom Sensor Maintenance and Spare Parts
This is the NMT539 Average Temp/Water Bottom Sensor maintenance and spare parts list.


NMT539 Average Temperature Converter Manual
Designed to assist the user in the installation, operation, maintenance, and troubleshooting of the Prothermo NMT539 Average Temperature Sensor/Water Bottom...

Technical Specifications

NMT539 Average Temperature and Water Bottom Sensors Technical Specifications
This is the NMT539 Average Temperature and Water Bottom Sensors Technical Specifications that explains purchasing options.
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