Type G | GUILCOR SENSORS

Type G
Temperature sensors

Specialized thermocouple for ultra high-temperature measurement up to 2300 °C, ideal for research and advanced materials processing.

Maximum precision
+/- 1,0°K

Minimum temperature
0°C

Maximum temperature
+2320°C

Minimum dimensions
0,5 x 50 x 5

Response time
Low

Internal Resistance
High

Linearity
High

Price
High

What is a Type G thermocouple ?

The type G thermocouple (tungsten-molybdenum alloy) is a sensor designed for extreme temperatures, up to +2,320 °C, in reducing environments or under vacuum.

Composed of W (pure tungsten) and Mo (pure molybdenum), it offers exceptional thermal resistance but cannot be used in open air.

It is distinguished by its high mechanical stability and resistance to violent thermal gradients, making it a preferred choice for energy and nuclear applications.

Operating principle

The G type operates according to the Seebeck effect, generating a voltage based on the temperature difference between the hot and cold junctions.

E = S × (T_hot - T_cold)

For type G:

S ≈ 17 µV/°C at 1,000 °C

Although its voltage is lower than that of types C or D, its mechanical strength and stability under thermal stress more than compensate for this point.

Technical specifications

Parameter	Typical Value
Measurement range	0 °C → +2 320 °C
Sensitivity	17 µV/°C at 1 000 °C
Tension at 1000 °C	≈ 12,3 mV
Tension at 2000 °C	≈ 24,6 mV
Tension at 2300 °C	≈ 28,3 mV
Oxidation resistance	Null (unusable in open air)
Response time (cable sheath Ø6 mm)	6 to 12 s
Reference standard	ASTM E230 (no official IEC standard)

Voltage / Temperature Curve

(Reference: Cold junction at 0 °C — ASTM E230 standard)

Type G produces a stable and monotonic voltage across its operating range, but slightly lower than that of types C and D.

Its drift remains very low even after several hundred hours at over 2,000 °C.

📈 General behavior:

From 0 to 2,320 °C → increasing voltage (~0 to +28.3 mV)
Average slope: ≈ 17 µV/°C at 1,000 °C
Drift: <0.05% after 100 h at 2,000 °C

💡 Type G is intended for extreme applications, where precision is secondary to physical resistance.

Compatibility / Compensation

The G type is not compatible with standard converters.

It requires specific electronics capable of handling low voltages and extreme temperature conditions.

It is imperative to use it in a high vacuum or a reducing atmosphere (dry hydrogen, pure argon, helium).

Application areas

⚙️ Fusion and processing of refractory metals

🔬 Plasma physics and vacuum processes

🧪 Nuclear research and advanced materials

🚀 Space propulsion and high-temperature energy systems

Should I choose a Type G thermocouple ?

Strengths points

🔥 Absolute heat resistance
→ It withstands temperatures close to the melting point of tungsten, which is over 2,000 °C.
🧱 Srobust structure
→ Their tungsten and molybdenum alloys resist thermal fatigue and rapid temperature shocks.
🧪 Ideal for vacuum and reducing environments
→ Stable in environments that noble metals cannot withstand, it is perfect for energy and nuclear research.

Weaknesses points

🌬️ Immediate oxidation in air
→ At temperatures above 500 °C, tungsten oxidizes and destroys the junction. Use exclusively in a controlled atmosphere.
💸 High cost and complexity
→ Between rare materials and specific electronics, it is a heavy investment reserved for critical applications.
📉 Lower sensitivity than other W–Re types
→ Srobustness remains conditioned on strictly controlled environments.

Useful information

Here is some useful information regarding Type G thermocouples.

Temperature ↔ Voltage Table (mV vs °C)

(Reference: cold junction at 0 °C — ASTM E230 standard)

Temperature (°C)	Tension (mV)	Temperature (°C)	Tension (mV)
0	0,000	1 400	17,1
400	4,8	1 600	19,8
800	9,7	1 800	22,3
1 000	12,3	2 000	24,6
1 200	14,8	2 300	28,3

💡 The tension of type G remains stable and monotonic up to the material limit (~2,320 °C).

Precision classes (according to ASTM E230)

Class	Tolerance (K)	Usage area	Description
Standard (C68)	±1,0 K ou ±0,25 %	0 → +2 320 °C	High precision
No IEC class	—	—	Non-standardized according to IEC 60584

🔹 The performance depends primarily on the environment (vacuum, inert gas) and not just on the sensor alone.

Application example – Voltage/Temperature calculation

Example 1 – Calculation of the generated voltage

Measured temperature: 1,800 °C

Cold weld at 0 °C

E = 22,3 mV

Cold welding at 25 °C → correction voltage ≈ 0.27 mV :

E_measured = 22,3 - 0,27 = 22,03 mV

✅ Actual voltage ≈ 22.03 mV

Example 2 – Calculating the temperature from a measured voltage

Measured voltage: 24.6 mV (cold junction at 0 °C)

→ According to the ASTM table:

T = 2000°C

✅ Measured temperature ≈ 2,000 °C

Integration diagram in an electronic system

The type G thermocouple generates a low voltage under extreme thermal conditions.

Its use requires isolated electronics that are protected against electromagnetic interference.

🔹 Typical components

Component	Function
Thermocouple type G (W / Mo)	Generate the Seebeck voltage
Isolated differential amplifier	Amplify the signal µV → V
Compensation sensor (NTC, integrated)	Correct the cold junction
24-bit high precision ADC	Convert the signal to digital
High Temperature Acquisition System	Calculate the final temperature using the ASTM table

🔹 Functional diagram (ASCII)

[HOT JUNCTION]──(Thermocouple G)──[ISOLATED AMPLIFIER]──[ADC]──[µCONTROLLER]
                                      │
                                      └──(Compensation sensor)

💡 Type G is the "last resort" thermocouple — used where no other material survives.