CNR4 Desiccant Replacement

Tools

• small blue handle channel locks
• Small Campbell Scientific Phillips #2 screwdriver
• Bubble Level
• Stubby #2 Phillips Screwdriver
• Optional but handy to have available tools in case of stripped screwheads
  • tap and die plus appropriate drill bit (plus spares) for those screw combinations.
  • cordless drill with charged battery
  • a larger drill bit (1/4" or less) to remove stripped head.

Supples

• Anti Corrosion Goo
• CNR4 Desiccant cartridge
  • Can purchase from Campbell Scientific or reuse one from crockpot.
• For Optional fix:
  • Small 8/32 or 10/32 or 6/32 or 4/32 machine screws, 1/2" or less in length.

Procedure 1: Desiccant Replacement

• Use small blue handle channel locks to loosen and remove the sensor cables.
• Rotate CNR4 on its slender cross arm 180 degrees to it is upside down.
• Use the small campbell scientific screwdriver to unscrew the small screws attached to the radiation shield. Place shield and screws on the ground
• Use the screwdriver to remove the machine screws (carefully!! they are made of a very soft metal that will try to strip if you aren't careful)
• place the screws on the radiation shield safely on the ground.
• carefully pry open the CNR4 bottom plate. There is an o-ring that might try to pop off.
• Inside the body of the sensors is a cylindrical white cartridge. Set it aside and replace it with a new / recently dried cartridge.
• carefully put things back together. Dab the tip of each machine screw with the anti-corrosion goo before screwing it in gently.
• once all screws are replaced, tighten them up again as if finishing lugnuts on a car wheel change.
• Next, rotate the sensor back to operating position.
• dab a bit more anti corrosion goo on the sensor cables and reconnect each.

Variation: Screws Strip

• If the screws strip out you'll obviously have a bit more work to do.
• Stop what you're doing.
• gently return any of the machine screws back into their original positions after dabbing with a bit of anti corrosion goo.
• completely remove the sensor from the mounting arm.
• Set on the ground / some clothing etc.
• Now, the screw that is stripped, you'll need to drill the head off. Drill with the larger bit until the head is gone.
• Change out to one of the drill bits paired with the tap and die. I leave it to you to select which combo. There are several because it is easy to break both the narrow diameter drill bits as well as the tap/die part.
• carefully drill a deepish hole with this drill bit adjacent to the stripped head. You will need to go pretty deep here in order to get full thread use.
• Use the tap and die to create threads.
• do a bit of testing with one of the replacement screws that it fits comfortably and tightly into this hole.
• Great, you're set. Now return to where you were and remove the machine screws and follow the original procedure above.

Procedure 2: Level the radiometer

• Once the sensor is back to original position finalize the level.
• use a bubble level or horizontal torpedo level by placing it on top of the sensor.
• there are seven separate screws at the tripod / tower end of the CNR4 cross arm. The four are used to keep the cross arm in a fixed spot. They form a rectangle.
• Three of them are slightly larger and screw into a nylon material. Ignore the one closest to the sensor. It is the pivot and should be tight. The two screws with spring control the level. The middle right handles left-right leveling (rotational). The one closest to tripod/tower handles up/down. Adjust until the bubble looks good.