1kΩ | GUILCOR SENSORS

1KΩ
Temperature sensors

Low-resistance NTC thermistor for fast temperature response in industrial control and power electronics applications.

Maximum precision
+/- 0,20°K

Minimum temperature
-50°C

Maximum temperature
+150°C

Minimum dimensions
2 x 10

Response time

Fast

Drift

Low

Self-warming
Low

Price
Low

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

Should I choose a 1KΩ sensor ?

Strengths points

⚙️ Excellent responsiveness
→ Response time of less than 1 second, ideal for dynamic systems such as rapid regulation or instant overheating detection.
💸 Economic and universal
→ The 1 kΩ NTC is inexpensive, standardized, and compatible with most electronic boards and microcontrollers.
🎯 Good accuracy around 25 °C
→ Simple digital transmission over 3 wires (CS, SCK, SO), compatible with Arduino, ESP32, Raspberry Pi, STM32, and most microcontrollers.

Weaknesses points

📉 Non-linear
→ His exponential response requires a lookup table or software calculation to obtain the exact temperature.
🌡️ Limited use beach
→ Less reliable beyond 150 °C, unlike RTDs (Pt100, Pt1000).
🔋 Sensitive to self-heating
→ A measurement current that is too high skews the measurement: care must be taken in sizing the voltage divider.

Useful information

Here is some useful information regarding the 1KΩ sensors.

Resistance Table – Temperature (R vs T)

(NTC 1 kΩ at 25 °C, beta constant = 3950 K)

Temperature (°C)	Resistance (Ω)	Temperature (°C)	Resistance (Ω)
−50	24 942	60	293
−40	15 803	70	221
−30	10 169	80	169
−20	6 708	90	130
−10	4 484	100	101
0	3 046	110	79,6
10	2 095	120	63,1
20	1 474	130	50,3
25	1 000	140	40,3
30	686	150	32,4
40	476	160	26,2
50	336	170	21,3

💡 Chaque décade de température divise environ par deux la résistance : une signature typique des NTC.

Tolerances and precision classes

Class / Tolerance	Tolerance at 25 °C (R25)	Error max on temperature (−40 → +125 °C)	Typical usage
±1 %	±10 Ω	±0,2 K	Precision measurement / instrumentation
±2 %	±20 Ω	±0,4 K	Fine regulation (HVAC, electronics)
±3 %	±30 Ω	±0,6 K	General public / general electronics
±5 %	±50 Ω	±1 K	Thermoprotection / rapid control

🔹 Glass-encapsulated thermistors (bead type) offer the best long-term stability (< 0.05 K/year).

Example of application – Steinhart–Hart equation

The standard Steinhart–Hart equation is:

1/T = A + B · ln(R) + C · [ln(R)]³

For an NTC 1 kΩ (β = 3950 K), the typical coefficients are:

A = 1.4051 × 10⁻³
B = 2.369 × 10⁻⁴
C = 1.019 × 10⁻⁷

🔹 Example 1: calculating the temperature from the resistance

Measured resistance: R = 686 Ω

ln(686) = 6.531

1/T = 1.4051×10^{-3} + 2.369×10^{-4}(6.531) + 1.019×10^{-7}(6.531)³ = 3.19×10^{-3}

T = 1 / 3.19×10^{-3} = 313.4 K = 40.4 °C

✅ Measured temperature: ≈ 40 °C

🔹 Example 2: calculation of resistance at a given temperature

Temperature: T = 80 °C = 353.15 K

R = R₂₅ × e^{β (1/T - 1/T₂₅)}

R = 1000 × e^{3950 × (1/313.15 - 1/298.15)} = 1690 Ω

✅ Expected resistance: ≈ 169 Ω

Integration diagram in an electronic system

The 1 kΩ NTC is typically used in a voltage divider connected to a microcontroller (10–12 bit ADC).

🔹 Typical components

Composant	Function
NTC 1 kΩ	Temperature detector
R fixed (1 kΩ)	Comparison reference
Microcontroller (ADC)	Tension reading
Power Supply 3.3 V / 5 V	Source stable
100 nF capacitor	Noise filtering

🔹 Functional diagram (ASCII)

 +3.3V / +5V
     │
   [Rfixe]
     │────► ADC (microcontroller input)
   [NTC 1kΩ]
     │
    GND

💡 The ADC measures the bridge voltage:

V_out = V_cc × (R_NTC / (R_fixe + R_NTC))

The microcontroller then converts this voltage into temperature using the Steinhart–Hart table or equation.