PTC Thermistor Overload
Protection for Test and Measuring instruments Meters
Test and Measuring instruments Meters Using PTC Thermistor for Overload Protection
Test and measuring instruments, such as oscilloscopes and digital multimeters, can be
easily damaged if excessive voltages are applied across their input terminals.
Simple and effective overload protection can be provided by connecting a high-voltage PTC
thermistor in series with the instrument; see Typical connection of the PTC thermistor for digital multimeter protection drawing. Under normal conditions, the resistance of the
PTC thermistor is low, so the test voltage will be measured by the instrument. Under an overload condition, the PTC thermistor will switch to its high-resistance state, absorbing the overload current and protecting the instrument. When the overload is removed, the PTC thermistor will return to its low-resistance state, ready to resume its protective function.
PTC thermistors Application
Over-Temperature/over-load protection for metering, low current signal protection, digital
signal protection against
Typical Connection of the PTC thermistor for Digital Multimeter Protection
Features and Benefits of PTC Thermistor for Test and Measuring Instruments Meters
Fast response time for rapid protection.
Automatic resetting once overload is removed.
Operates on DC or AC voltage.