Kelvin (TK) Probe Assembly

related links

<DIY LM34 probe construction>
<DIY LM334 temperature sensor probe construction>. (pdf)
<DIY TMP17 temperature sensor probe construction>. (pdf)

The AD590, the LM334 and the TMP17 are electrically very similar to the AD592. The difference is primarily in the package. The alternate documents discuss the construction of alternate probes. Why all three? At one point in time, the supply of AD592s dried up, and we had to look around for alternatives to use for the Earth Measurements curriculum. (The LM34 is quite different electrically, as it is a voltage output device instead of current output.)

Overview

The AD592 temperature sensor will be attached to wires of the cable using shink+solder preforms and a heat gun. The cable sheath will be pulled up over the connection and the probe tip will be sealed by using adhesive line shring tubing, or by dipping in rubber compound.

Parts for TK temperature probe construction

AD592 temperature sensor
2 solder/strink preforms
2-conductor cable of the desired length, Belden 8442 or equiv.
rosin flux
heat shrink gun

The center wire of the AD592 is trimmed off. The other two wires are trimmed to 7/16" (1/16" shorter than the length of the solder/shrink preforms). The two wires in the cable are stripped back 3/16" and tinned, and dipped in rosin flux if available. Leave about 3/8" of insulated wires exposed beyond the outer cable jacket.

Attach the sensor to the cable

Put the tinned cable ends inside the two solder preforms along with the two wires of the temperature sensor. Be sure to observe the correct polarity for the color coding, as shown. Observe the tinned wires from the cable are centered on the solder preforms inside the heat-shrink sleeve.

 

Apply heat carfully, using a precision heat gun and a shield to direct the heat.

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Observe carefully for the solder melting, to affix the wires of the sensor to the cable.

When the assembly has cooled off, test it for proper operation. The current output from the sensor at room temperature should be approximately 300 microamps.

Insulate the proble assembly:

Push the outer cable jacket up on the probe assembly so that the outer jacket covers and strengthens the wire junction. You may wish to apply hot-melt glue to the junction as you push the cable up over the junction. To complete the assembly, apply a short length of heat shrink tubing, with adhesive liner, or dip the probe tip in rubber "tool dip" coating.