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Open circuit or short circuit faults in the temperature-sensing elements of thermal resistors are quite common. Currently, many factories resolve such faults by simply replacing the components. In this article, CHANGHUI Instruments shares the steps and methods for fixing open circuit or short circuit faults in thermal resistors, which can help improve the repair skills of instrument technicians. ◆How to determine whether a thermal resistor is short-circuited or open-circuited? First, remove the thermistor element from its protective tube, and use a multimeter set to the R×1 range to measure its resistance value. If the reading is ∞, it indicates an open circuit; otherwise, if the resistance value is zero or less than R0 (for Pt100 platinum thermistors, R0 = 100Ω, and for Cu50 copper thermistors, R0 = 100Ω), it indicates a short circuit. Thermal resistors: yunrun.com.cn/product/list_80.html. Handling of cases where the heating element of a copper thermal resistor is broken. If the insulating paint on the enameled wire of the copper thermal resistor element has peeled off and green rust is present, it indicates that the copper resistance element is damaged and can no longer be used; in such cases, it should be discarded. If minor peeling of the insulating paint on the copper resistive element is found, it can be repaired and used again. Methods for repairing a broken copper resistor: ① Locate the end portion on the outer layer of the copper resistor component ； ②Unwind the coil until the broken wire is reached ； ③Solder using a soldering iron, then check whether there is a conductive path from the tail end to the lead wire; if not, continue to disassemble in order to find another broken connection until everything is connected ； ④Rearrange and wind the removed enameled wire in a double-layer winding pattern (make sure to insulate the welded ends with varnish) ； ⑤The entire copper resistance element is coated with varnish for insulation ； ⑥Place it in the oven to dry. ◆Handling of short circuits in the temperature-sensing element of copper thermoresistors: Short circuits in copper thermoresistor elements are usually caused by reduced insulation or short circuits resulting from moisture or the removal of insulating varnish. If the component is damp, it can be dried in an oven at a temperature of 80-100°C for 1-2 hours. If the short circuit is caused by the removal of the insulating varnish from the component, then: ① Locate the end portion on the outer layer of the component ； ②Unwind the coil until the varnish comes off (usually on the outer layer) ； ③Use varnish to insulate the areas where the insulation has come loose ； ④Rewind the unwound thread. ◆Handling of open circuits in the temperature-sensing elements of platinum resistance thermometers: Currently, the structural types of industrial platinum resistance thermometer temperature-sensing elements commonly used in China include those with mica frames, glass frames, ceramic frames, as well as integrally sintered platinum resistance elements with external windings and thin-film elements. The latter types cannot be repaired in either the case of an open circuit or a short circuit; only platinum resistance elements with a mica skeleton structure can be repaired and used again. http://yunrun.com.cn/upload/201808/30/201808301630571618.png Repair methods for mica-frame platinum resistance elements: ① Remove the split insulating porcelain beads of the fixing clamping pieces ； ②Rotate the clamping piece by 90° around the rivet axis of the riveted clamping piece ； ③Using the same method, the insulating mica sheet is rotated by 90°, at which point the platinum wire wrapped around the serrated mica framework becomes visible ； ④Examine the broken area of the platinum wire under a magnifying glass; if the break occurs between two platinum wires, it can be welded using arc welding with a voltage of around 6V. Refer to the article \"Introduction to Simple Welding Methods for Thermocouples\" for guidance ； If there is a break between the platinum wire and the lead wire, it can be welded using arc welding with a voltage of around 10V. It should be noted here that the platinum wire in mica platinum resistance elements is very thin (usually only 0.03–0.07 mm), so special care must be taken during maintenance operations; forceps should be used only, and direct contact with the fingers is not allowed, otherwise cleaning is necessary. During welding, the wire can only be loosened by 1-2 teeth; it cannot be completely removed, otherwise annealing treatment is required. ◆Handling of short circuits in the temperature-sensing element of platinum resistance thermometers: The insulation between the platinum wires in such elements is provided by serrated mica sheets. If the serrations are damaged or the platinum wire becomes loose and touches, causing a short circuit, it should be separated using forceps. It should be emphasized here that, whether after a short circuit or after repairing the platinum resistance temperature sensor element affected by a short circuit, its resistance value (R0) at 0°C must be checked to determine whether it meets the specified requirements. yunrun.com.cn/tech/2482.html ◆ What issues should be considered when servicing thermistor temperature sensing elements? Thermal resistance temperature-sensing elements are detection components with high precision, as well as excellent stability and reliability, in temperature measurement instruments; therefore, troubleshooting faults in such thermal resistance elements requires particular care and attention. ①After removing the protective tube from the thermistor temperature-sensing element, any rust or oil contamination inside the protective tube should be cleared away. ②When inspecting or repairing the temperature-sensing element of a thermal resistor, for platinum thermal resistors, one should not touch the platinum wire with bare hands, nor should the wire be removed ； For copper thermistors, it is not necessary to remove all the enameled wire from the skeleton. ③When adjusting the resistance value (R0) at 0°C, any increase or decrease in the R0 value should be made at the end of the thermoresistive temperature-sensing element. If the R0 value is too low, for copper thermistor temperature-sensing elements, it is possible to increase it by using enameled wire of the same diameter for welding ； For the platinum resistance temperature sensor element, it can be slightly elongated using forceps in order to increase its value. ④If the lead wires are found to be too short when installing the thermistor element in the protective tube, for copper thermistors, copper wires of the same diameter can be used to extend them ； For platinum thermoresistors, silver wires of the same diameter are used to extend them (welded using an arc welder with a voltage of around 12V).