What is a MAX6675 sensor ?
Le NTC 1 kΩ est une thermistance à coefficient de température négatif dont la résistance nominale est de 1 000 Ω à 25 °C.
Sa résistance chute de manière exponentielle avec la température, ce qui en fait un capteur simple, précis et économique pour les mesures jusqu’à 150 °C.
Operating principle
The resistance-temperature relationship follows the Steinhart–Hart law:
1/T = A + B · ln(R) + C · [ln(R)]³
with:
- TTT: absolute temperature (in kelvins)
- RRR: resistance in ohms
- A, B, CA, B, CA, B, C: model-specific coefficients for NTC
In a simpler approximation (linear zone around 25 °C):
R(T) = R₂₅ × e^{β (1/T - 1/T₂₅)}
• R₂₅ = 1000 Ω
• β ≈ 3500 – 3900 K (depending on manufacturer)
Technical specifications
| Parameter | Typical value |
Nominal resistance (25 °C) |
1 000 Ω ±1 % |
| Constant β | 3500–3900 K |
Sensitive material | Metallic oxide (Mn, Ni, Co) |
| Type of case | Epoxy / glass / pearl |
Maximum measurement current | 1 mA (to limit self-heating) |
Response time | 0.3 to 1 s depending on the medium |
Linearity | Exponential (non-linear) |
Operating temperature | −50 → +150 °C |
Lifetime | 100,000 thermal cycles |
Wiring Configuration
The NTC 1 kΩ are generally 2-wire (simple voltage reading).
For accurate measurements :
- a divider bridge with a reference resistor is often used,
- or a 10/12 bit analog-to-digital converter on a microcontroller.
Schematic diagram:
+Vcc │ [Rfixe] │────► ADC (µC) [NTC] │ GND
Self-warming
The measurement current generates internal thermal dissipation.
For a current of 0.5 mA, the power dissipated is approximately 0.25 mW, causing negligible self-heating (< 0.05 °C).
Application Areas
⚙️ Thermal regulation systems (HVAC, power electronics)
💧 Immersion probes for fluids
🔋 Thermal compensation in power supplies
🧠 Electronic boards, overheating detectors
🏭 Industrial and automotive applications
