DIY Temperature Probe

A reliable temperature probe that you can make yourself is a thermocouple, which is essentially two dissimilar metal wires joined in a circuit. The operation of thermocouples is based on the "Seebeck effect," a small voltage that develops in response to differences of temperature between the junctions of the dissimilar metals. For every metal-pair, the voltage developed in the circuit is a function of the temperature difference.

Different types of thermocouples are used depending on the application. Type T, consisting of copper wire and constantan wire, is one of the most common and is useful in the temperature range 330 to 660 degrees F.

Things You'll Need

  • Type T Duplex Insulated thermocouple wire, 10 inches
  • Wire stripper/cutter
  • Pliers, 2 pair
  • Soldering iron
  • Rosin-core solder (40% lead, 60% tin)
  • Heat-shrink tubing, diameter 3/16 inches, length 1 1/2 inches
  • Lighter
  • Glass tubing, diameter 3/8 inches, length 6 inches
  • Electrical tape
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Instructions

    • 1

      Strip 1 inch of insulation from the outer insulation cover and from both thermocouple wires using the wire strippers.

    • 2

      Hold the wires securely in a pair of pliers at the end of the bared wire. With your other hand, twist the bared wires together using the other pair of pliers, 3 or 4 turns until the connection is tight with maximum contact between the metals.

      Trim the metal-ends with the wire cutters to produce an even connection.

    • 3

      Apply a drop of solder to the tip of the twisted wires to ensure a good, secure contact; use the minimum amount of solder necessary. The twisted-wire connection serves as the tip of the temperature probe.

    • 4

      Fit the heat shrink over the probe tip so that it overhangs the tip by 1/4 inch. Ignite the lighter and wave the flame back and forth along the length of the heat-shrink until it has shrunk to form a tight wrap around the probe tip. Quickly crimp the heat-shrink with pliers at the end of the probe tip and hold them closed until the molten plastic hardens, then cut the excess from the probe tip.

    • 5

      Insert the probe into the glass tube and position it so that the base of the heat-shrink is even with a tube-end. Secure the probe by wrapping electrical tape around the tube-end and the heat-shrink below the probe tip. Do not apply tape to the probe tip itself.

    • 6

      Apply tape in a similar fashion to secure the opposite end of the tube. The wire extending from this end connects to a multimeter or other instrument.

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