Type K | GUILCOR SENSORS

Type K
Temperature sensors

Versatile thermocouple for general-purpose temperature measurement from −200 °C to +1260 °C in industrial and OEM applications.

Maximum precision
+/- 1,5°K

Minimum temperature
-200°C

Maximum temperature
+1260°C

Minimum dimensions
0,25 x 25 x 2

Response time
High

Internal Resistance
Medium

Linearity
High

Price
Low

What is a Type K thermocouple ?

The type K thermocouple is the most universal and versatile of thermocouples.

Made of nickel-chrome (Chromel) and nickel-aluminum (Alumel), it combines stability, low cost, and a wide measurement range.

It is the global industrial standard, used in furnaces, engines, cooking appliances, as well as in laboratories and test benches.

Its popularity comes from its chemical robustness, resistance to oxidation, and good thermal performance in most environments.

Operating principle

The K type exploits the Seebeck effect, like all thermocouples:

a temperature difference between the hot junction and the cold junction creates a voltage proportional to this difference.

E = S × (T_hot - T_cold)

For type K:

S ≈ 41 µV/°C around 0 °C

This coefficient varies slightly with temperature but remains sufficiently linear for industrial applications.

Technical specifications

Parameter	Typical Value
Measurement range	−200 °C → +1 260 °C
Sensitivity	41 µV/°C to 0 °C
Tension at 100 °C	≈ 4,10 mV
Tension at 500 °C	≈ 20,64 mV
Tension at 1,000 °C	≈ 54,89 mV
Oxidation resistance	Excellent
Response time (cable sheath Ø3 mm)	0,5 to 3 s
Reference standard	IEC 60584-1, ASTM E230

Voltage / Temperature Curve

(Reference: Cold junction at 0 °C — IEC 60584-1 standard)

Type K offers a nearly linear curve across its useful range.

It is the most balanced reference in terms of voltage amplitude, cost, and durability.

📈 General behavior:

From −200 to 0 °C → negative voltage (~−5.9 mV to 0 mV)
From 0 to 1,260 °C → positive voltage (~0 to +54.9 mV)
Average slope: ≈ 41 µV/°C

💡 It is the "go-to" thermocouple: reliable, stable, and compatible with almost everything.

Compatibility / Compensation

The K type is fully compatible with the majority of devices on the market (controllers, displays, data acquisition modules).

Cold junction compensation is automatically managed by many integrated circuits (MAX31855-K, AD8495-K, LTC2983).

Its stability and robustness make it a default standard in many industrial applications.

Application areas

⚙️ Industrial processes (furnaces, engines, heat exchangers, molds)

🔬 Laboratories and thermal testing

🔧 Maintenance, HVAC, food industry

🧪 Control equipment and routine calibrations

Should I choose a Type K thermocouple ?

Strengths points

🔥 The universal industrial standard
→ Present in all sectors, it is recognized for its robustness, reliability, and low cost.
🔥 Large measurement range
→ From -200 °C to +1,260 °C: type K covers both cryogenic cold zones and industrial furnaces.
⚙️ Excellent stability / price ratio
→ A durable, accurate, and easy-to-maintain sensor, perfect for repeated measurements or long-term installations.

Weaknesses points

⚡ Long-term drift
→ In a reducing atmosphere or with strong thermal cycles, the signal may drift slowly.
🌡️ Slight non-linearity above 1,000 °C
→ The sensitivity decreases slightly, requiring software correction for very precise applications.
💨 Sensitive to sulfate atmospheres
→ Sulfur compounds quickly deteriorate Chromel — to be avoided in certain chemical industries.

Useful information

Here is some useful information regarding Type K thermocouples.

Temperature ↔ Voltage Table (mV vs °C)

(Reference: cold junction at 0 °C — IEC 60584-1 standard)

Temperature (°C)	Tension (mV)	Temperature (°C)	Tension (mV)
−200	−5,891	200	8,138
−100	−2,585	400	16,397
0	0,000	600	24,906
100	4,095	800	33,275
200	8,138	1 000	41,276
300	12,209	1 200	49,093
400	16,397	1 260	52,410

💡 Type K is one of the few thermocouples that can be used at both −200 °C and +1,200 °C.

Accuracy classes (IEC 60584-1)

Class	Tolerance (K)	Usage area	Description
Class 1	±1,5 K ou ±0,4 %	−40 → +1 000 °C	High precision
Class 2	±2,5 K ou ±0,75 %	−200 → +1 200 °C	Industrial standard
Class 3	±2,5 K ou ±1,5 %	−200 → 0 °C	Low temperatures

🔹 Class 1 is favored for modern acquisition systems and demanding applications.

Application example – Voltage/Temperature calculation

Example 1 – Calculation of the generated voltage

Measured temperature: 600 °C

Cold weld at 0 °C

E = 24,906 mV

If the cold weld is at 25 °C, equivalent voltage ~1,000 mV:

E_measured = 24,906 - 1000 = 23,906 mV

✅ Actual voltage ≈ 23.91 mV

Example 2 – Calculating temperature from a measured voltage

Measured voltage: 41.276 mV (cold junction at 0 °C)

→ According to the IEC table:

T=1000°C

✅ Measured temperature ≈ 1,000 °C

Integration diagram in an electronic system

The type K thermocouple generates a voltage of a few tens of millivolts, proportional to the temperature.

It requires a differential amplifier, cold junction compensation, and a high-resolution A/D converter.

🔹 Typical components

Component	Function
Thermocouple type K (Chromel / Alumel)	Generate the Seebeck voltage
Differential amplifier (AD8495-K, INA333, etc.)	Amplify the signal µV → V
Compensation sensor (NTC or integrated)	Correct the cold junction
ADC 16–24 bits	Digitize the signal
Microcontroller / Acquisition Module	Convert the voltage to temperature using IEC table

🔹 Functional diagram (ASCII)

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

💡 Thanks to its wide compatibility, type K is often the default choice for multipoint measurement systems.