What is an NTC sensor?

NTC (Negative Temperature Coefficient) is a type of thermistor, an electronic component whose resistance changes with temperature. In the case of NTC, resistance decreases as temperature increases.

Relationship of resistance to temperature

• At low temperatures (e.g., -10°C), resistance is high.
• As the temperature rises, e.g., to +50°C, resistance gradually decreases.

This relationship is not linear, but it can be described by a special formula (e.g., the Steinhart-Hart equation or exponential formula). In practice, manufacturers of NTC sensors provide a table of resistance values as a function of temperature.

This characteristic makes NTC sensors commonly used in:

• Thermostats and temperature controllers,
• Consumer electronics (e.g., chargers, batteries),
• Heating and air conditioning systems.

Use of NTC sensors in external heating systems

NTC sensors are widely used in external heating systems, such as:

• Driveway and sidewalk heating systems (preventing icing),
• Pipe heating (protection against freezing),
• Roof and gutter de-icing systems,
• Temperature regulation in heat pumps and gas boilers.

Role of NTC sensors in heating systems

NTC sensors play a key role in automatic temperature regulation, allowing for:

1. Monitoring ambient temperature – e.g., a sensor mounted on the driveway measures surface temperature.
2. Detecting temperature drops to a risk level – if the temperature drops below 3°C, the heating system can automatically turn on.
3. Optimizing energy consumption – when the temperature rises (e.g., to 5°C and above), the system turns off heating, saving energy.
4. Protecting system components – in heated pipes, NTC sensors prevent overheating and failures.

Example of operation: driveway heating system

1. An NTC sensor is installed in the driveway surface.
2. A drop in temperature below 0°C detected by the sensor activates the heating system.
3. When the temperature rises to 5°C, the heating turns off.
4. If a moisture sensor is additionally used, the heating system activates only when it is wet (which prevents wasting energy on dry ground).

Thanks to this application, NTC sensors provide efficient and energy-saving control of heating systems. We encourage you to watch the video material about driveway heating systems.

Precise operation of the NTC sensor in the driveway heating system

1. Installation of the NTC sensor in the driveway surface

The NTC sensor is placed directly in the driveway surface or nearby. Its task is to continuously monitor the surface temperature. It can be installed, for example:

• In the gaps between paving stones,
• Under a layer of asphalt or concrete,
• In special heating modules.

The sensor is connected to the heating system controller, which analyzes its readings.

2. How does the sensor “know” to turn on the heating?

The NTC sensor is a thermistor, a resistor whose resistance changes with temperature. In the case of NTC (Negative Temperature Coefficient), resistance decreases as temperature increases and increases when temperature drops.

Step by step:

1. Temperature drops (e.g., to -1°C).
2. Sensor resistance increases – since NTC operates inversely to a standard conductor, its resistance rises at low temperatures.
3. The system controller analyzes the sensor's resistance and checks if it corresponds to the set temperature threshold (e.g., 0°C).
4. When resistance reaches a certain level corresponding to a temperature of 0°C, the controller activates the heating system by sending a signal to a relay or contactor.
5. The driveway heating turns on, preventing icing.

3. How does the sensor know to turn off the heating?

After the heating is turned on, the surface temperature begins to rise, causing the following changes:

1. The driveway temperature rises to 5°C.
2. Sensor resistance decreases because the NTC thermistor reacts inversely to the increase in temperature.
3. The controller compares the resistance value with the set cutoff threshold (e.g., 5°C).
4. When the resistance corresponds to a temperature of 5°C, the controller turns off the heating system – indicating that there is no longer a risk of icing.
5. The driveway remains dry and safe, and the system saves energy because it does not operate unnecessarily.

4. Example of an NTC sensor in the TERMOFOL offer

Ground sensor ETOG-56T is a durable and reliable moisture and temperature sensor designed for installation in the mounting sleeve ETOK-T.

It is designed for outdoor use, where it effectively supports de-icing systems for driveways, sidewalks, and stairs.

Thanks to its resistance to extreme conditions, it operates in a temperature range from -50°C to +70°C and features high IP68 tightness. Its compact dimensions are 30 mm in height and 60 mm in diameter.

How to measure the resistance of an NTC sensor

The resistance measurement of the NTC sensor is conducted using a multimeter set to measure resistance in the range of 20 kΩ. The resistance measurement of the floor sensor is for control and informational purposes and aims, similar to the measurement of the heating system resistance, to rule out damage to the connection cable (e.g., tearing it while pulling it out) or the NTC sensor itself.

Approximate resistance values depending on the installation surface temperature are provided in the table below. The tolerance of the measured value is +/- 10%.

The resistance measurement of the sensor is performed after connecting its terminals to the multimeter clips. Do not perform the measurement while holding both terminals with your fingers, as human skin has some resistance, which may lead to distorted measurement results due to the formation of a parallel resistance circuit.

Role of the NTC sensor resistance

• At low temperature (e.g., -1°C), resistance increases, which activates the heating.
• At higher temperature (e.g., 5°C), resistance decreases, which turns off the heating system.
• The entire process is automatic and precise, as the controller converts the resistance value into temperature and makes decisions based on that about turning the heating on or off.

Thanks to this relationship, there is no need to use complicated temperature sensors – a simple, cheap, and reliable solution based on the NTC thermistor is sufficient. Contact the experts at TERMOFOL for more useful information!