Type C | GUILCOR SENSORS

Type C
Temperature sensors

Pt10 temperature sensors provide accurate and reliable temperature measurement for industrial applications requiring low nominal resistance.

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
Low

Linearity
Low

Price
High

What is a Type C thermocouple ?

The type C thermocouple is designed for extreme temperatures — up to +2,320 °C.

It is made from tungsten-rhenium alloys:

W-5%Re / W-26%Re (tungsten with 5% and 26% rhenium).

It is the preferred sensor in inert or vacuum atmospheres, where noble metals like platinum would lose their properties.

It offers remarkable stability and excellent mechanical resistance at high temperatures.

Operating principle

Like all thermocouples, type C relies on the Seebeck effect: a temperature difference between the junctions generates a voltage proportional to this difference.

E = S × (T_hot - T_cold)

For type C:

S ≈ 20 µV/°C at 1,000 °C

It produces a moderate voltage but maintains exceptional linearity and stability up to 2,300 °C — where most other types literally melt.

Technical specifications

Parameter	Typical Value
Measurement range	0 °C → +2 320 °C
Sensitivity	20 µV/°C at 1 000 °C
Tension at 1000 °C	≈ 14,80 mV
Tension at 2000 °C	≈ 29,12 mV
Tension at 2300 °C	≈ 33,10 mV
Oxidation resistance	Null in open air (use under vacuum or inert gas)
Response time (6 mm diameter sheath)	5 to 12 s
Reference standard	ASTM E230 (no official IEC standard)

Voltage / Temperature Curve

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

Type C offers a linear and stable curve between 400 °C and 2,300 °C, with very low drift even over the long term.

📈 General behavior:

From 0 to 2,300 °C → increasing voltage (~0 to +33 mV)
Average slope: ≈ 20 µV/°C at 1,000 °C
Drift: <0.05% after 100 hours at 2,000 °C

💡 Type C is an extreme thermocouple: high precision, great stability, but demanding on operating conditions.

Compatibility / Compensation

The type C is not compatible with oxidizing environments: it must be used in an inert atmosphere or under vacuum (argon, helium, dry hydrogen).

It requires a precision differential amplifier and stable cold junction compensation.

Compatible modules include, in particular, the LTC2983 and specialized high-temperature measurement chains.

Application areas

🚀 Aerospace, turbines and rocket engines

🔬 High-temperature laboratories, plasma and high vacuum

⚙️ Metallurgy, arc furnaces, melting of refractory metals

🧪 Nuclear industry and advanced materials

Should I choose a Type C thermocouple ?

Strengths points

🔥 King of Extreme Temperatures
→ With an operating limit of +2,320 °C, it surpasses all conventional thermocouples.
⚗️ Remarkable stability under vacuum
→ Ideal for inert environments, it maintains its accuracy even after long thermal exposures.
🧱 Ultra-resistant materials
→ Tungsten-rhenium alloys retain their mechanical properties at very high temperatures.

Weaknesses points

🌬️ Incompatible with air
→ The oxidation of tungsten in open air destroys the probe within a few minutes at high temperature.
💸 Very expensive and fragile
→ Its complex manufacturing and rare materials make it a sensor reserved for critical applications.
⚙️ Specific electronics required
→ Requires a calibrated acquisition chain and special connectors to support the voltage level and temperature.

Useful information

Here is some useful information regarding Type C 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	20,13
400	5,33	1 600	22,73
800	10,52	1 800	25,70
1 000	14,80	2 000	29,12
1 200	17,50	2 300	33,10

💡 The tension increases almost linearly up to 2,300 °C, without significant drift.

Precision classes (according to ASTM E230)

Class	Tolerance (K)	Usage area	Description
Standard (C68)	±1,0 K ou ±0,25 %	0 → +2 300 °C	High precision
No IEC class	—	—	Non-standardized according to IEC 60584

🔹 The actual precision mainly depends on the quality of the vacuum and the electronic stability of the system.

Application example – Voltage / temperature calculation

Example 1 – Calculation of the generated voltage

Measured temperature: 1,800 °C

Cold weld at 0 °C

E = 25,70mV

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

E_measured = 25,70 - 0,27 = 25,43 mV

✅ Actual voltage ≈ 25.43 mV

Example 2 – Calculating the temperature from a measured voltage

Measured voltage: 29.12 mV (cold weld at 0 °C)

→ By consulting the ASTM table:

T=2000°C

✅ Measured temperature ≈ 2,000 °C

Integration diagram in an electronic system

The type C thermocouple generates a low but stable voltage at very high temperatures.

It requires an isolated differential amplifier and a high-precision acquisition system.

🔹 Typical components

Component	Function
Thermocouple type C (W5Re / W26Re)	Generate the Seebeck voltage
Isolated differential amplifier	Amplify and protect the signal
Compensation sensor	Correct the cold junction
ADC 24 bits	Convert the voltage into digital data
Microcontroller / Oven Controller	Calculate the final temperature using the ASTM table

🔹Functional diagram (ASCII)

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

💡 Type C is the thermocouple for extreme conditions: it exceeds 2,000 °C where all others fail.