Which mounting type should I choose for my application?

Fixed screw thread (240 series) is the most common for standard process pipes. Fixed flange (440 series) is ideal for high-pressure vessels. Adjustable pipe joint (54 series) allows depth adjustment after installation. Fixed threaded pipe (82 series) is used when compact sensing is needed.

What is the maximum operating pressure?

Fixed screw thread (240), fixed flange (440), and adjustable pipe joint (54) types are rated for nominal pressure of 4 MPa or less, covering most standard industrial process conditions.

How do I specify the correct model number?

Follow the naming convention: W (temperature) + R (thermocouple) + material code + element count + mounting code + 4 (Ex box) + tube diameter + optional suffix. Example: WRN2-241G means Type K, dual element, fixed screw, Ex box, diameter 20, fast response.

HMK Temperature Sensors

Explosion-Proof Thermocouples

Q: What NEPSI explosion-proof grades are available for these thermocouples?

Three grades are certified by NEPSI: dII BT4 (Certificate GYB997151) for general industrial gas environments, dII CT5 (Certificate GYB02475) for more volatile gas groups, and iaII CT6 (Certificate GYB05363X) for intrinsically safe applications in the most hazardous zones.

Q: What is the difference between dII BT4, dII CT5, and iaII CT6?

The 'd' prefix indicates flameproof (explosion-proof) enclosure type. BT4 covers gas groups IIA/IIB with temperature class T4 (135°C max surface). CT5 covers group IIC with T5 (100°C max surface) for hydrogen and acetylene environments. The 'ia' prefix in iaII CT6 indicates intrinsically safe design suitable for Zone 0 areas.

Q: Can these thermocouples work with a 4-20mA transmitter?

Yes. Add the B suffix to any model number to include an integrated SBW head-mounted temperature transmitter within the explosion-proof junction box, converting the thermocouple signal to standard 4-20mA output.

NEPSI-certified explosion-proof thermocouples for hazardous area temperature measurement in petroleum, chemical, and gas processing facilities. Types K, N, E, J, T with flameproof (dII) and intrinsically safe (iaII) protection, covering 0°C to 1300°C.

Types K/N/E/J/T 0–1300°C Range NEPSI Certified dII BT4/CT5/iaII CT6 IP65 Protection ≤4 MPa Rating

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Overview

Explosion-proof thermocouples utilize interval explosion-proof technology with sealed junction boxes featuring flame-cooling gaps. The design principle confines any potential spark or arc within the sealed enclosure and cools any flame passing through the narrow gap to prevent external explosion propagation. This proven method complies with GB3836 and international standards for Zone 1 and Zone 2 hazardous area applications.

Key characteristics include spring-loaded pressure sensing elements that maintain excellent anti-vibration performance under mechanical stress and thermal cycling. The large measurement range across five thermocouple types (K, N, E, J, T) covers temperatures from 0°C to 1300°C. All models feature high mechanical strength construction with robust sheath materials (1Cr18Ni9Ti or 0Cr25Ni20 stainless steel) and are protected against moisture ingress with IP55 or IP65 ratings depending on the mounting configuration.

These thermocouples comply with IEC 584, GB/T16839-1997, GB26786-2011, and Gb3836 standards. Insulation resistance is rated at ≥1000MΩ (1 meter cable) or ≥100MΩ (10 meter cable) measured at 500±50V DC. Three NEPSI certification grades are available: dII BT4 for general industrial environments, dII CT5 for more volatile gas groups, and iaII CT6 for intrinsically safe Zone 0 applications in the most hazardous areas.

Technical Specifications

Specification	Value
Standards	IEC 584, GB/T16839-1997, GB26786-2011, Gb3836
Thermocouple Types	K (WRN), N (WRM), E (WRE), J (WRF), T (WRC)
Temperature Range	0 to 1300°C (varies by type)
Accuracy Class	IEC 584 Class I & II
Insulation Resistance	≥1000MΩ (1m) / ≥100MΩ (10m) at 500±50V DC
Sheath Material	1Cr18Ni9Ti / 0Cr25Ni20
Sheath Diameter	Φ3, Φ4, Φ5, Φ6, Φ8 (adjustable) / Φ16 (fixed)
Process Connection	M20×1.5, NPT1/2, M27×2, G3/4
Protection Grade	IP65 (anti-spring), IP55 (waterproof)
NEPSI Certifications	dII BT4, dII CT5, iaII CT6
Thermal Response	<90s standard, <24s fast (G variant)
Nominal Pressure	≤4 MPa

Tolerance Levels (IEC 584)

Type	Grade	Class I Tolerance	Class I Range °C	Class II Tolerance	Class II Range °C
K (WRN)	N	±1.5°C / ±0.004\|t\|	-40~+375 / 375~1000	±2.5°C / ±0.0075\|t\|	-40~+333 / 333~1200
N (WRM)	M	±1.5°C / ±0.004\|t\|	-40~+375 / 375~1000	±2.5°C / ±0.0075\|t\|	-40~+333 / 333~1200
E (WRE)	E	±1.5°C / ±0.004\|t\|	-40~+375 / 375~800	±2.5°C / ±0.0075\|t\|	-40~+333 / 333~900
J (WRF)	F	±1.5°C / ±0.004\|t\|	-40~+375 / 375~750	±2.5°C / ±0.0075\|t\|	-40~+333 / 333~750
T (WRC)	C	±0.5°C / ±0.004\|t\|	-40~+125 / 125~350	±1.0°C / ±0.0075\|t\|	-40~+133 / 133~350

Explosion-Proof Classification

NEPSI Certifications

Grade	Certificate Number	Application
dII BT4	GYB997151	General industrial gas environments, Zone 1/2
dII CT5	GYB02475	Volatile gas groups (H2, acetylene), Zone 1/2
iaII CT6	GYB05363X	Intrinsically safe, Zone 0/1/2

Ex Grade Classification

Grade	MESG	Gas Group
A	≥0.9mm	Most gases (methane, propane)
B	0.5–0.9mm	Hydrogen, ethylene
C	≤0.5mm	Acetylene, carbon disulfide

Temperature Groups

Group	Max Surface Temp	Application
T1	450°C	High-temperature processes
T4	135°C	Standard industrial (dII BT4)
T5	100°C	Volatile gases (dII CT5)
T6	85°C	Intrinsically safe (iaII CT6)

Model Selection Guide

Model Format: W-R-[Material]-[Count]-[Mounting]-4-[Tube]-[Additional]

Material Code

M	NiCr-NiSi (Type N)
N	NiCr-NiSi (Type K)
E	NiCr-CuNi (Type E)
C	Cu-CuNi (Type T)
F	Fe-CuNi (Type J)

Mounting Code

2	Fixed Screw Thread (240 series, M27×2 / G3/4)
4	Fixed Flange (440 series)
5	Adjustable Pipe Joint (54 series, M20×1.5)
8	Fixed Threaded Pipe (82 series, M20×1.5)

Optional Suffixes

G	Fast response (<24s) variable cross-section sheath
B	Built-in SBW 4-20mA transmitter

Example: WRN₂-241G = Type K, Dual element, Fixed screw thread, Ex box, Φ20, Fast response

Mounting Type Specifications

a) Fixed Screw Thread Type (240 Series)

Model	Type	Temp Range	Response	Sheath Dia
WRN2-241	K	0–1000°C	<90s	Φ16
WRM2-241	N	0–1100°C	<90s	Φ16
WRE2-241	E	0–800°C	<90s	Φ16

b) Fixed Flange Type (440 Series)

Model	Type	Temp Range	Connection	Pressure
WRN2-441	K	0–1000°C	Flanged	≤4 MPa
WRM2-441	N	0–1100°C	Flanged	≤4 MPa
WRE2-441	E	0–800°C	Flanged	≤4 MPa

c) Adjustable Pipe Joint Type (54 Series)

Model	Connection	Sheath Dia	Length Range	Protection
WRN-54	M20×1.5/NPT1/2	Φ3–Φ8	250–1150mm	IP65
WRM-54	M20×1.5/NPT1/2	Φ3–Φ8	250–1150mm	IP65
WRE-54	M20×1.5/NPT1/2	Φ3–Φ8	250–1150mm	IP65

d) Fixed Threaded Pipe Joint (82 Series)

Model	Connection	Sheath Dia	Protection	Length Range
WRN-82	M20×1.5	Φ3–Φ8	IP65	245–1149mm
WRN-83	NPT1/2	Φ3–Φ8	IP55	245–1149mm
WRM-82	M20×1.5	Φ3–Φ8	IP65	245–1149mm

Key Features

Flameproof Construction

Sealed explosion-proof junction box with flame-cooling gap design. All spark and arc-generating components confined within the flameproof enclosure per GB3836 standards.

NEPSI Certified

Three certified explosion-proof grades: dII BT4 (GYB997151), dII CT5 (GYB02475), and iaII CT6 (GYB05363X). Suitable for Zone 1 and Zone 2 hazardous areas.

Spring-Loaded Element

Pressure-spring type sensing element provides excellent anti-vibration performance and maintains reliable thermal contact even under mechanical stress and thermal expansion.

Multiple Mounting Options

Four mounting configurations available: fixed screw thread (240), fixed flange (440), adjustable pipe joint (54), and fixed threaded pipe joint (82). Standard and NPT connections.

Wide Temperature Range

Full coverage from 0°C to 1300°C across five thermocouple types. Type N reaches 1100°C, Type K to 1000°C, Type E to 800°C, Type J to 600°C, Type T to 350°C.

Fast Response Option

G-suffix variable cross-section models achieve thermal response time under 24 seconds, compared to standard 90 seconds. Available for all mounting types.

Applications

Oil Refineries

Atmospheric and vacuum distillation column temperature monitoring, catalytic cracking reactors, hydrocracking units, and crude preheat trains. dII BT4 grade covers most petroleum refinery gas groups.

Chemical Plants

Reactor temperature control, distillation column profiles, heat exchanger monitoring, and exothermic reaction management. Multiple connection types fit standard chemical process piping.

Gas Processing

Natural gas dehydration, sweetening processes, compression station monitoring, and LNG facility temperature control. dII CT5 grade provides protection for more volatile gas mixtures.

Offshore Platforms

Topside process temperature measurement, FPSO operations, gas turbine monitoring, and subsea equipment. IP65 protection withstands marine salt spray environments.

Pharmaceutical

Solvent recovery systems, API synthesis reactors, drying ovens in hazardous classified areas. iaII CT6 intrinsically safe option available for Zone 0 applications.

Coal & Mining

Underground coal mine ventilation temperature, methane drainage monitoring, and coal preparation plant process control. Type I electrical equipment rated for underground use.

Frequently Asked Questions

Three grades are certified by NEPSI: dII BT4 (Certificate GYB997151) for general industrial gas environments, dII CT5 (Certificate GYB02475) for more volatile gas groups, and iaII CT6 (Certificate GYB05363X) for intrinsically safe applications in the most hazardous zones.

The ‘d’ prefix indicates flameproof (explosion-proof) enclosure type. BT4 covers gas groups IIA/IIB with temperature class T4 (135°C max surface). CT5 covers group IIC with T5 (100°C max surface) for hydrogen and acetylene environments. The ‘ia’ prefix in iaII CT6 indicates intrinsically safe design suitable for Zone 0 areas where explosive atmosphere is continuously present.

Fixed screw thread (240 series) is the most common for standard process pipes with M27×2 or G3/4 connections. Fixed flange (440 series) is ideal for high-pressure vessels and reactors. Adjustable pipe joint (54 series) with M20×1.5 allows depth adjustment after installation. Fixed threaded pipe (82 series) with Φ3–Φ8mm sheath is used when compact sensing is needed in smaller process connections.

Yes. Add the ‘B’ suffix to any model number to include an integrated SBW head-mounted temperature transmitter within the explosion-proof junction box. This converts the thermocouple millivolt signal to a standard 4-20mA output for direct PLC/DCS connection over long cable runs.

Fixed screw thread (240), fixed flange (440), and adjustable pipe joint (54) types are rated for nominal pressure ≤4 MPa. This covers most standard industrial process conditions. For higher pressure applications, contact our engineering team for custom solutions.

Follow the model naming convention: W (temperature) + R (thermocouple) + material code (M/N/E/C/F) + element count (blank for single, 2 for dual) + mounting code (2/4/5/8) + 4 (Ex junction box) + tube diameter (0 for Φ16, 1 for Φ20) + optional suffix (G for fast response, B for built-in transmitter). Example: WRN₂-241G means Type K, dual element, fixed screw, Ex box, Φ20, fast response.

Need Explosion-Proof Temperature Measurement?

Our engineering team specializes in explosion-proof thermocouple solutions for hazardous area applications. Contact us for custom configurations, NEPSI certification documentation, special mounting requirements, or volume pricing for your project.

Our engineers typically respond within 12 business hours with detailed technical specifications and pricing.

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