The resistance of thermistors is significantly more temperature-dependent than conventional resistors. Thermistors are classified with the conduction model. Thermistors with a high positive temperature coefficient (PTC) exhibit more resistance at higher temperatures. Thermistors with a negative temperature coefficient (NTC) exhibit less resistance at higher temperatures. Therefore, a PTC thermistor’s resistance is inversely proportional to temperature. Read More…
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PTC thermistors are used as self-resetting overload protectors and self-regulating heating components. NTC thermistors are used as over-current limiters and temperature sensors. Depending on the type of probe used, a thermistor's operational temperature range normally falls between 100 °C and 300 °C.
A thermistor’s components impact the relationship between temperature and resistance. Metal oxide compounds, binders, and stabilizers are combined to make thermistors, which are subsequently sliced into chips, left in disc form, or given other shapes. The precise ratio of the composite components determines their resistance/temperature "curve." This ratio affects thermistor functionality, so manufacturers carefully regulate this ratio.
Working Principle of a Thermistor
Thermistors operate under the principle that a temperature change causes resistance to change. A thermistor will begin self-heating its components as the ambient temperature changes. The resistance value changes to accommodate this shift in temperature. The thermistor type being used affects this modification. The following section lists the resistance temperature properties of various thermistors.
Types of Thermistors
PTC Thermistors are primarily divided into two categories for industrial use. The first is referred to as "Silistors", after the sensitivity of silicon resistors. The positive temperature coefficient for silistors is 8% per degree Celsius. The gadget moves to a negative temperature index zone if the temperature exceeds 175 degrees Celsius. Shifting type PTC thermistors are the other subcategory of PTC thermistors. They are built of ceramic materials because ceramic has great resistance to even minor temperature fluctuations. The material is additionally doped with dopants to give them a semi-conductive characteristic.
Applications of PTC Thermistors
PTC thermistors are used as fuse-like circuit protection devices. Due to the device's resistive nature, heat builds up when current flows through it. As a result, if the PTC thermistor receives excessive electricity, it will heat up and become more resistant. To limit the voltage and current that can flow.
PTC Thermistors are also used as a timer in a CRT monitor's degaussing coil circuit. The PTC thermistor and the degaussing coil receive an initial current when a CRT display is turned on. Due to the large size of the PTC thermistor, the device's resistance rises as the current enters. As a result, the degaussing coil quickly shuts off as heat builds up. A degaussing coil is required to reduce the constant magnetic field gradually.
NTC Thermistors are used in two ways, depending on how electrodes are applied to the ceramic body. Bead NTC thermistors are usually used in the industrial sector. Bead thermistors include glass-coated beads, bare Beads, shock-absorbent beads, and more. The NTC Thermistors with metallic coating surface contacts are classified differently. These types of thermistors can be surface mounted or attached utilizing spring contacts.
Applications of NTC Thermistors
NTC Thermistors are used to measure applications in mid to low-temperature ranges. NTC Thermistors can control the abrupt surge in a supply circuit current. They have a high resistance value. As the device warms up, the resistance steadily lowers. As the resistance falls, the circuit resumes its normal operation, and the large current passes through it without endangering the other components of the circuit.
NTC Thermistors are used to gauge incubator temperatures and determine coolant and oil temperatures in automobile engines.