High Quality Thermistor Certification

Q&A

Jun 07, 2024

1. Both NTC and PTC are thermistors. What is the difference between them?

Answer: Thermistors are resistors whose resistance changes with temperature. According to the different temperature coefficients, they are divided into positive temperature coefficient thermistors (PTC) and negative temperature coefficient thermistors (NTC). The typical characteristic of thermistors is that they are sensitive to temperature and show different resistance values at different temperatures. The higher the temperature of the positive temperature coefficient thermistor (PTC), the greater the resistance value, while the higher the temperature of the negative temperature coefficient thermistor (NTC), the smaller the resistance value. They are both semiconductor devices.

In addition, the two thermistors have the following three main differences in characteristics:

(1) The resistance values of PTC thermistors and NTC thermistors change in opposite directions with temperature.

(2) Compared with NTC thermistors, the temperature coefficient of resistance of PTC thermistors will change suddenly near the Curie point.

(3) The resistance value of NTC thermistors only decreases with increasing temperature, while the resistance value of PTC thermistors changes dramatically at the Curie point. It can be regarded as being controlled by temperature and acting like a conductive switch.

 

2. What is the minimum size of the red enameled wire head used in the electronic thermometer?

Answer: Because the electronic thermometer uses a high-precision temperature measurement NTC thermistor product, the ultra-small temperature measurement NTC thermistor chip can be 0.4*0.4*0.25mm, the wire diameter of the lead is 0.1mm, the minimum head is 0.7mm, the response speed is fast, the thermal time constant is 0.6s, and the temperature measurement accuracy reaches 0.012℃. It can solve the shortcomings of the existing electronic thermometers such as low temperature measurement accuracy, inaccurate temperature measurement, and slow response speed, and realize large-scale production.

 

3. What is the difference between thermistors and ordinary resistors?

Answer: There is a big difference between thermistors and ordinary resistors, that is, the temperature coefficient of thermistors is much larger than that of ordinary resistors, that is, thermistors are particularly sensitive to temperature changes. When the temperature changes, the resistance value of the thermistor will change significantly immediately. When the temperature changes, the resistance value of the thermistor will change according to the expected law. Generally speaking, the higher the temperature of a positive temperature coefficient thermistor (PTC), the greater the resistance value, while the higher the temperature of a negative temperature coefficient thermistor (NTC), the smaller the resistance value.

 

4. What is the structure of a thermistor?

Answer: Thermistors are mainly composed of three parts: thermistor chip, lead wire, and shell. Thermistors are generally made into two-terminal devices, but there are also three-terminal or four-terminal devices. Two-terminal and three-terminal devices are directly heated, that is, they directly obtain power from the circuit. Four-terminal devices are indirectly heated, and according to different requirements, thermal resistors can be made into different shapes and structures, including disc type, column type, bead type, armored type, and thick film type.

 

5. What are the classifications of thermistors?

A: According to the structure and shape, thermistors are divided into disc-shaped (sheet-shaped), cylindrical (column-shaped), circle-shaped (washer-shaped) and other types; according to the sensitivity of temperature change, they are divided into high-sensitivity type (sudden change type) and low-sensitivity type (slow change type) thermistors; according to the heating method, they are divided into direct-heated thermistors and indirectly-heated thermistors; according to the temperature (temperature change) characteristics, they are divided into positive temperature coefficient (PTC) and negative temperature coefficient (NTC) thermistors.

 

6. What are the precautions for using NTC thermistors?

A: (1) Do not use NTC thermistors at excessively high power. 

(2) Do not use them outside the operating temperature range.

(3) Do not apply sudden temperature changes that exceed the upper and lower limits of the operating temperature range.

(4) When using NTC thermistors alone as the main control element of the device, in order to prevent accidents, be sure to take comprehensive safety measures such as setting up a "safety circuit" and "using NTC thermistors with equivalent functions at the same time".

(5) When using in a noisy environment, please take measures to set up a protective circuit and shield the NTC thermistor (including the wire).

(6) When using a sheathed NTC thermistor in a high-humidity environment, only the sheath head should be exposed to the environment (water, moisture), and the sheath opening should not be directly exposed to water or steam.

(7) Do not apply excessive vibration, impact, or pressure, and do not excessively stretch or bend the wire.

(8) Do not apply excessive voltage between the insulation and the electrode. Otherwise, poor insulation may occur.

(9) When wiring, ensure that "water", "steam", "electrolyte", etc. do not penetrate into the wire end (including the connector), otherwise poor contact may occur.

(10) Metal corrosion may cause equipment malfunction, so when selecting the material, ensure that there is no contact potential difference between the metal sheathed and screw-fastened NTC thermistor and the metal parts to which it is installed.

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