Vishay Temperature Sensor in an Integrated Power Box

Challenge

The temperature sensor assemblies were intended to be mounted on busbars using lugs, but the sharp edges of aluminum busbars can damage the wire insulation material of thermistor assemblies. This was problematic, considering the wire positions wouldn't be fixed, as these systems can experience high mechanical shock and vibration forces during operation. Additionally, the busbars could be subjected to high temperatures, which meant that standard plastic wire insulation alone wasn't viable due to the possibility of being melted and causing a short.

Because two sensors of the same style would be employed in two locations in the system but with different R25 values and cable lengths, it was vital to distinguish between the two assemblies for selection and placement during manufacturing. The final design had to be AEC-Q200 compliant, offer a high isolation voltage of 2.7kV_AC up to +150°C, and use an M4 mounting screw size.

Solution

Vishay's engineers manufactured an assembly based on the NTCALUG91A standard lug sensors with an M4 screw mounting. The finished product featured two sensors with different cable lengths and wire colors mounted on the same connector. To protect the connection cables from sharp edges on the busbars, they are constructed in glass fiber insulation tubes. This wire casing masked the wire insulation color and prevented visual inspection, requiring another solution for differentiating the two sensors. A colored dot was added on the neck of the lug for one of the two sensors, which is easily detected via automated visual inspection.

Benefit

This solution offered the engineers precise and secure temperature control of their integrated power box, preventing damage to the sensors and connecting cables while allowing for variable design positions that improve the reliability of the final application.