Arctic Hyporheic Zone Project
I. Preparing Thermocouples for Installation
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Thermocouples (TCs) are simple sensors that will be used to determine the temperature of the streambed in various locations. TCs are stimulated by the datalogger and multiplexer with a small voltage. The multiplexer and datalogger then read the voltage drop that comes back from the excitation and computes a resistance. That resistance is then correlated to a reference thermistor that is located in the datalogger housing, which provides a reference temperature. The datalogger then computes a temperature at the TC location.

Preparation of TCs is simple, but requires the utmost care. Remember, these sensors will have to withstand installation into the streambed and the harsh conditions throughout deployment. We will not be able to check the integrity of the sensors once they are deployed. Click on images for larger view.

Step 1. Prepare Wire.
Obtain the TC wire (from Omega), which is composed of 2 small wires (22 gauge), a blue-sheathed copper wire and a red sheathed lead-based wire. Cut to desired length with wire cutters.
Omega TC wire
TC end stripped
 At both ends, strip back the outer insulation about 3 cm. At one end, strip the entire exposed length of the red and blue wires, this will be the TC end. At the other end, strip only about 0.5 cm of the red and blue insulation.
At the TC end (that with about 3 cm stripped back), twist the wires into a tight braid.
braided stripped wire
solder the braided wire
 Now solder the braided wire. Be sure the solder is clean and silvery.
After it has cooled, cut back the length to about 1 cm.
trim the soldered wire
Step 2. Protect the TC.
We prefer to protect the TC with some insulation. Use some thick, sticky electrical tape to wrap around the soldered end of the wire. Wrap this on very tightly.
insulate the soldered end
apply heat shrink
 Next, delicately slide on a piece of heat-shrink tubing.
Be sure that the heat shrink tubing extends from the end of the TC to a little ways up the wire.
adequate heat shrink tubing
shrink it!
 Now carefully use a heat gun to shrink the tubing on to the protected TC.
Now you have one TC completed.
final product - one TC
Step 3. Assemble TC strings.
Now you need to put several of the TCs together to form a TC string, which will be deployed into the streambed. Place several prepared TCs on a table and align the TCs and wires such that the TCs are some interval apart (say 20 cm). Then use wire ties to connect the TC wires together, just above each TC. Also use duct tape to keep the wires together in between TCs.
assemble a TC string
arctic river scene
 Be sure to mark a known distance up the wire with duct tape. This length should be about the same as the length of the sleeve you will be using to install the TC strings in the streambed (see the installation page for details). You will need this when you install the TC string to know how deep each TC is located.

Fianlly, be sure to test and label each TC after the string has been assembled. You can connect the leads of each TC to a temperature probe (Omega probe in lab already) and verify that a reading is being registered. Then grab the TC end that you think is connected to those leads and you should see a change in the reading, by several degrees in ~30 sec. These values aren't accurate, but they are indicative of function. Then be sure to LABEL the lead end of the TC. This is very important because you will need to know which wire goes to which TC and which channel in the multiplexer. Our current nomenclature is "XN", where "X" is a letter identifying the string (A, B, C, etc.) and "N" is a number for each TC, where 1 is the deepest (when installed).

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This page was created 02-Aug-2003.
This page was last updated 05-Sept-2007.
Questions? mgooseff@engr.psu.edu