 QA

# How are thermistors rated? This is determined by using Ohm's law E ÷ I = R (E = volts, I = current, R = resistance). The D.C. is then calculated by dividing the power dissipated in the NTC thermistor by the temperature difference between the two measured temperatures. Power is calculated by using Ohm's law, P = E x I.

Which is better NTC or PTC thermistor? As temperature rises, resistance increases from low to high and blocks the overcurrent. Specific scenarios require a PTC thermistor over an NTC thermistor. These include equipment with a near-zero reset time, extreme temperature conditions, and systems that experience frequent shorts.

How are NTC specified?

Since one NTC resistance change is approximately equivalent to a 1° temperature change, NTC is useful in specifying temperature tolerances. NTC's are given on the Vishay Dale Specification Sheet in 10 degree increments; however, the NTC may be calculated at any temperature point using a 1 °C R-T table.

Are all thermistors the same?

There are many different types of thermistors but they all work on the same principle: variable resistance based on temperature. There are basically two categories of thermistors of which all types fall under; NTC and PTC. Depending on your particular application you may opt for one thermistor over another.

What is a 10k NTC thermistor?

– A 10k NTC thermistor displays 10k ohm resistance at 25°C and has a negative relationship between temperature and resistance. – A 100k PTC thermistor displays 100k ohm resistance at 25°C and has a positive temperature-resistance relationship.

Before any heat is applied to the thermistor, its resistance value should be very closely near its rated resistance value. So, for example, if we are testing a 10KΩ thermistor, before we apply any heat, its resistance value should be very close to 10KΩ. If you're in a relatively warm room, it may be about 9.3KΩ.

How is thermistor used in measuring temperature?

Thermistors change resistance with temperature changes; they are temperature-dependent resistors. They're perfectly suited to scenarios where one specific temperature needs to be maintained, they're sensitive to small changes in temperature. They can measure liquid, gas, or solids, depending on the type of thermistor.

How do you determine thermistor type?

To determine whether the sensor is a thermistor or RTD, as well as the type, you must measure the resistance between the two different-coloured wires: An RTD PT100 will have a resistance of 100 ohms at 0 °C. An RTD PT1000 will have a resistance of 1,000 ohms at 0 °C.

Which thermistor is best?

NTC Thermistors offer excellent immunity to electrical noise and lead resistance.

Why NTC thermistor is used over PTC?

A 10k NTC thermistor displays 10k ohm resistance at 25°C and has a negative relationship between temperature and resistance. – A 100k PTC thermistor displays 100k ohm resistance at 25°C and has a positive temperature-resistance relationship.

Related Questions

### How are NTC thermistors rated?

The rated resistance of the NTC thermistor is at 25 ºC, so de-rating of the resistance rating will be needed for ambient temperatures above 25 ºC, as the resistance of the thermistor will be lower. Ametherm (resistance/Time) R/T curves will dictate how much de-rating is needed.

### What are the different types of thermistor?

There are two types of thermistors: Negative Temperature Coefficient (NTC) and Positive Temperature Coefficient (PTC). With an NTC thermistor, when the temperature increases, resistance decreases. Conversely, when temperature decreases, resistance increases.

### How do you read the thermistor value?

Thermistor Specifications
Usually expressed in percent (e.g. 1%, 10%, etc). For example, if the specified resistance at 25°C for a thermistor with 10% tolerance is 10,000 ohms then the measured resistance at that temperature can range from 9,000 ohms to 11000 ohms.

### How do you size a thermistor?

This is determined by using Ohm's law E ÷ I = R (E = volts, I = current, R = resistance). The D.C. is then calculated by dividing the power dissipated in the NTC thermistor by the temperature difference between the two measured temperatures. Power is calculated by using Ohm's law, P = E x I.

### What is an NTC thermistor?

An NTC thermistor is a temperature sensor that uses the resistance properties of ceramic/metal composites to measure the temperature. Our full spectrum NTC sensors offer many advantages in temperature sensing including miniature size, excellent long-term stability, high accuracy and precision.

### What are NTC thermistors used for?

NTC thermistors are resistors with a negative temperature coefficient, which means that the resistance decreases with increasing temperature. They are primarily used as resistive temperature sensors and current-limiting devices.

### What is the resistance of a thermistor?

Thermistors are characterised by their base resistance as well as their “B” value. The base resistance, for example, 10kΩ, is the resistance of the thermistor at a given temperature, usually 25oC so is defined as: R25.

### What is a thermistor and how does it work in determining temperature?

Thermistors are temperature-dependent resistors, changing resistance with changes in temperature. They are very sensitive and react to very small changes in temperature. They are best used when a specific temperature needs to be maintained, and when monitoring temperatures within 50°C of ambient.

### What is thermistor and its uses?

Thermistors are used as temperature sensors. They can be found in every day appliances such as fire alarms, ovens and refrigerators. They are also used in digital thermometers and in many automotive applications to measure temperature.

### How are thermistors specified?

Thermistors may be specified with either a temperature tolerance or a resistance tolerance at either a single temperature point or over a temperature range.

### How do I know my NTC and PTC thermistor?

As their name indicates the resistance of an NTC thermistor will decrease with temperature and the resistance of a PTC thermistor will increase with temperature. Both PTC as well as NTC thermistors can be roughly checked by using an analogue multimeter.

### Which temperature sensor is best?

The most well-known are Pt100 (with a resistance of 100 ohms at 0°C) and Pt1000 (with a resistance of 1,000 ohms at 0°C). The Pt1000 offers better accuracy and a larger tolerance to long wire lengths than the Pt100. Compared to thermocouples, resistance sensors offer better accuracy and a more linear response.

### What is the difference between a NTC thermistor and a PTC thermistor?

They are available with either a negative temperature coefficient, (NTC) of resistance or a positive temperature coefficient (PTC) of resistance. The difference being that NTC thermistors reduce their resistance as the temperature increases, while PTC thermistors increase their resistance as the temperature increases.

### How do you read a thermistor?

Thermistor Specifications
Usually expressed in percent (e.g. 1%, 10%, etc). For example, if the specified resistance at 25°C for a thermistor with 10% tolerance is 10,000 ohms then the measured resistance at that temperature can range from 9,000 ohms to 11000 ohms.

### How do I choose a PTC thermistor?

For example: – A 10k NTC thermistor displays 10k ohm resistance at 25°C and has a negative relationship between temperature and resistance. – A 100k PTC thermistor displays 100k ohm resistance at 25°C and has a positive temperature-resistance relationship.