California Cooperative Oceanic Fisheries Investigations

     The CalCOFI method of termination is one of many techniques used to interface a CTD on a conductive wire. Over the years, our method has evolved - this documents the current 2010 technique.
     Since many ships have a 3-conductor wire (3 internal wires plus shield), each wire is terminated separately, isolating it from the other wires. Then, if any conductive wire fails over the course of the cruise, it can be disconnected from the CTD pigtail without having to re-terminate. Although each of the 3 wires & shield has its own connector, the CTD pigtail combines two wires for the signal, reducing resistance. The remaining conductor is used as ground and can be paired with the shield if desired. CalCOFI prefers not to use the shield for ground unless a conductive wire is unavailable.
     On vessels with a single-wire conductive sea-cable, the standard termination (signal=conductive wire; ground=shield) method is used.

Part 1: The termination
(click photos for larger image)

1. Inspect the conductive wire on the winch drum and cut off any severely rusty wire.
2. Pull at least 3m (~10ft) of wire on deck to allow termination on the wet lab bench top, if available.
3. Unwrap outer sheath ~2 m (6ft) length

   

4. Unwrap inner sheath enough to remove inner conductive wire core then unravel 3 adjacent shield strands along with the core.
5. Trim the core & 3-strands of inner shield to ~50cm (20") from the unwrap point.
   
6. Rewrap the unravelled shield back into a single, coreless wire, leaving the conductive core & 3 strands exposed. Tape the frayed end of the wire with Super 33 black electrical tape.
   

   
   

7. Strip ~10cm (4") of the black, outer protective core. This is difficult & best done in small, 0.75cm (3/8") increments using coax cable stripper adjusted to cut the outer cover without cutting into the inner conductive wires. Careful when persuading off the black plastic covering you do not damage the conductive wires. 
   

   

8. Strip ~2.5cm (1") off the three inner conductors.
9. Strip ~2.5cm (1") off four Impulse connectors; forth one is for the shield.
10. Use 95% alcohol on a large Kim-wipe to de-grease all the wire surfaces for good adhesion of shrink-tubing, tape, electrical putty & coating. Let dry a few minutes.
11. Conduct the 9 volt battery conductive wire test. At the CTD-sea cable junction box free the ends of all conductive wires. Attach a 9 volt battery to two conductive wires at the CTD end. Note the colors of the wire and, moving back to the junction box, find the two wires with ~+9 volts on a multimeter. Record their color then switch the battery to the other conductor until you've color keyed the three conductive wires and shield. On some ships the wire colors in the junction box agree with the conductive cable. The voltage reading will verify you have a good conductivity - check for 'cross-talk' by measuring all the wires for voltage leakage. If any wire does not conduct the proper voltage or has a stable voltage reading when it is not connected to the battery, further testing is required to determine if that wire should be excluded from the termination.
    

    
    

12. Be sure the Impulse connectors have connector sleeves, color coded with tape to match the junction box wires, before soldering. Use the wire color key from step 11 to coordinate the connector color to the proper junction box wire.
13. Slip adhesive-lined shrink tubing, cut ~1cm (0.5") shorter than the strand, onto the wire; solder connectors, paying particular attention to not melt shrink tube.
14. Let the weld cool for ~30 seconds then slid the shrink tubing evenly over the weld. Apply heat, starting from the middle and working toward each end, until all air is expelled. Adhesive should seep from both ends of the shrink tubing insuring a good moisture barrier.
15. For the shield connection, snip off one shield strand then emory cloth the ends of the remaining two stands, removing all oxidation & rust. Using a crimp connector, crimp the Impulse connector wire to the two shield strands and fill the crimp with solder. Shrink tubing does not need to be applied to this connection.
16. Smoothly (no bubbles) apply Scotch-Coat electrical coating to each wire individually. Scotch-coat ~7cm (3") up onto the black core & Impulse connector insulation. Keep all wire separated as they dry 20-30mins.
17. Split 3/4" insulating tape in half with sharp scissors so you have a 3/8" wide piece about 16cm (6") long. Starting ~2.5cm (1") up on the (loose end) connector's black insulation, tightly wrap the wire with insulating tape sticky side up. Wrap down onto the thinner wire using the insulation tape to reinforce and strengthen the thin diameter. Stretch and tightly wrap your way up to the black plastic core, stopping where the three conductors come together. Repeat for the two other conductors.
18. For the shield connector, start wrapping 2.5cm up on the Impulse connector's black insulation. Tightly wrap the wire to prevent moisture intrusion under the connector insulation then continue up & over the crimped connector.
19. Apply Scotch-coat to all the individual wires once more and let dry 20-30 minutes.
20. (Optional) Repeat step 15, adding a second layer of insulating tape onto the three main conductive wires. On the third wire, instead of stopping where the three wires meet, continue ~4cm up onto the black plastic core with the final wrap
21. Apply Scotch-coat to the four wires and let dry.

22. Take a piece of electrical putty tape equal to the length of the termination, trim off the four corners and wrap it around all wires like a taco, not, however, before twisting all wires together to form a loose braid. Pinch the putty edges together forming a gap-less tube around the termination. Squeeze the putty into the air pockets between the wires - try to eliminate as much trapped air as possible.
23. Wrap the putty 'tube' with Super 33 electrical tape, starting at the middle and working toward the loose end, wrapping very tightly.  When you reach near the edge, leave 0.5cm of the putty unwrapped, then wrap back to the center normally (tight but not stretching the tape); once back to center, repeat the technique on the other half, wrapping tightly to near the edge then back to middle normally until you've completely double-wrapped the termination. It is important to leave each end open so as the putty compresses, it can seep out the ends.
24. Apply a final coat of Scotch-coat, sealing the tape surface.
    
25. Loosely wrap the ground wire to the outside of the termination then tape it in place so all connectors are gathered together.
     

Part II: The Sea-cable Connection

1. Using the cable color key from Part 1 step 11, at the junction box, combine two conductors for signal (usually red & white)  then the third conductor to ground. Using the shield is optional - on some ships, it generates electrical noise (spikes).
2. At the CTD, plug in the appropriate connectors to the CTD pigtail - the signal and com (common or ground) pairs are indicated on the pigtail sleeves. There are four connectors on the CTD-pigtail but they combine into signal & common.
3. Turn on the deck unit, if everything is connected properly, the front LED panel should read something other than '0000000000'. If you get zeros, the most common problem is reversal signal & common.

Part III: The Rigging

1. Disconnect the CTD pigtail from the termination securing the sea-cable to the rosette frame.
2. Lacing the wire down through the center of the rosette, wrap the termination and coreless sea-cable once around the CTD frame and through the CTD cage, paying careful attention to the placement and orientation of the termination.  Adjust the length so the termination & pigtail are easily secured, protected, but accessible when cable harnesses are in place.
3. Cable tie the sea-cable in place for ease of attachment.

    

4. Place 1 large cable clamp on the wire and the fish cage (photo 09).  This cable clamp immobilizes the conductive wire so when the CTD-rosette is lifted, there is no tension on the termination. Tighten securely but do not over-tighten or you may interrupt the electrical continuity & create a short. 
5. Place two additional smaller clamps on the wire loop about 12cm (5") from the end of the loop and about 40cm (15") from the end of the loop.  Note that the 40cm clamp is not visible in this picture.  This is the main safety for the CTD should the the chinese fingers fail.
6. Cable tie the sea-cable loop to the cage, making sure there are no significant movement in the cables.
7. Attaching the sea-cable to rosette - hold the sea-cable up over the center & allow enough slack so when lifted, there is plenty of slack between the shackle and the CTD. This determines the attachment point of the cable grip ('Chinese fingers') so mark it with black tape.  The sea-cable can then be move to chest-level for installation.

8. Secure the stainless thimble in the loop of the cable grip with black tape. Then begin wrapping the chinese fingers around the cable. Towards the end, it becomes increasingly difficult to seat the chinese fingers.  You may have to use the angle head screwdriver/tack puller tool to finish the job. 

 

9. Put a small hose clamp or sturdy cable tie at the top of the chinese fingers to keep from unwrapping.
   
10. Wrap yellow tape and hi-vis zip ties around wire to aid in visual determination of the 'just below surface' mark.
11. Attach the chinese finger to the shackle such that the wire is clear of the nut & cotter pin.
12. Using 'tuna-cord' or thin nylon line, tie the sea-cable slack out-of-the-way of the bottle lanyards.

Tips & Reminders

• The conductive core has a clear tape length index. When unwrapping the core, save the length reading for the ship's cable log.
• Wire colors can change from the sea-cable to the junction box because the sea-cable conductors are soldered to the junction box wires at the winch's slip rings. This termination can become faulty over the course of the cruise so when troubleshooting signal interruptions, take that into consideration.
• The longer the length of exposed wire core you leave when unwrapping the shield, the more chances of reterminating without have to unwrap the shield. 50cm (~20") of exposed wire core is enough to reterminate at least once.
• Cut 2 strands of inner sheath approx the same length as the conductive core for ground crimp connection.
• Once the inner connectors are stripped to bare wire, wipe all surfaces of the wire with 95% ethanol to ensure a clean, grease free connection.
• Make sure the work space is fairly clean and the work surface is covered with paper towels to catch electrical coating drips.
• Keep the electrical tapes clean of lint or other debris so wraps are bubble & lint free.