Identify temperature sensor
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It is quite likely not a thermocouple, but a thermistor:

  • A thermocouple would look like a small blob of metal. The tip of your temperature sensor appears to be a glass bead, which is a commonly used way to encase thermistors.

  • Thermocouples are polarized. The fact that the wiring is not "directional" suggests it is a thermistor.

  • Thermocouples are used in high-temperature applications (such as a high-temperature hotend for printing specialty materials), where a thermistor would break down. The bed is not such a high-temperature application.

You can easily verify this with a multimeter. If it was a thermocouple, its resistance would be near zero. With a thermistor, you should see a decent amount of resistance (most 3D printing thermistors are 100k at room temperature).