It can be necessary to exchange a loadcell in DroughtSpotter systems. Loadcells can be damaged by excess weight or simply can fail on the long term. In DroughtSpotter V2 and higher, loadcells can be easily exchanged by the user in a few minutes.

What you need

To exchange a loadcell you will need a screw driver  (Philips #2), a set of metric Allen Key Set and a sidecutter. Some cable ties can be handy too.

Safety First

Before doing any work on the system please make sure that:
  1. There are no experiments running on the system by other users
  2. The system is powered off and disconnected from the main socket. Never perform any work when there is power on the system
  3. Prevent that the system can be powered on by somebody else while you are working on it
  4. The valve of the unit you are working on is switched to closed

Getting Started

To exchange a loadcell you will need to access the system from the top as well as the front. To do that you will need to remove the front panel (white plate with DroughtSpotter sign on it) of the system. First, dismount the lever of the valve of the DroughtSpotter unit located at the bottom right corner of the front plate by unscrewing it. Second, remove all screws that fix the front plate with the Allen Key.

After you have removed all screws you can just take off the front plate. You should see the inside of the DroughtSpotter with the loadcell cables coming from the table plate and going into the Junction Box. 

Unmounting the loadcell

We can now start to exchange the loadcell. First remove the stainless steel cover plate of the loadcell you want to exchange. To do that, simply remove the two screws holding it with an Allen key. Take of the cover plate. Underneath the cover plate is a 6mm stainless steel spacer (U shape or simple square depending on the DroughtSpotter version) which you also have to remove. It is fixed by the same screws as the cover plate. After you have removed the cover plat and spacer you should see the loadcell. Afterwards, remove the second pair of screws that fixes the junction box on the ground plate. To do that, access the loacell from bottom and remove the two screws holding it in place.

Disconnect the loadcell

Follow the cable down to the junction box and cut it loose when necessary with the side cutter. Remember where the cable was so that you can put the new cable in the same position. The loadcell cable is connected to the Junction with an M12 connector. Trace the cable to the junction box and remove it by unmounting the M12 connector from the junction box. 

The loadcell should now be disconnect from the system and you should be able to pull out the cable and remove the cell. 

Mount new cell

Mounting the new cell follows the same procedure as unmounting the old cell, just in a different order. First put the new cell in place and pull the cable through the hole in the base plate. Note that there is an arrow engraved on the loadcell that shown in what direction it should be mounted. The arrow should point downwards when its mounted. Second, mount the two bottom screws to fix the loadcell in place. Now you can start to wire the cables of the loadcells and fix them in the DroughtSpotter. It is easiest if you follow the path of the old cable and fix it with cable ties where needed. Please make sure that the cable is not 'pulling' on the loadcell. This will influence the weighing results. 

Finally put the spacer and cover plate back on the load cell and fix them with the two screws and an Allen Key. When you fix them double check that the cover plate doesn't touch the POM plate on the edges (see red circle as an example. The distance between POM plate and cover plate should be the same all around the cover plate. If you have a physical contact between the two, the weighing result will drift. 

Finally, put the front plate back onto the system and mount the lever of the unit valve. Also make sure that you switch water and power back on after all work is finished.

After mounting a new loadcell you will need to calibrate the cell to work properly. To do that check the calibration tutorial.