Whenever possible, purchase a sensor with the desired cable length. Some sensors have a user-specified cable length, whereas other sensors have a set cable length.
Sometimes, an old cable can be replaced with a new, longer cable.
Generally, additional cable cannot be spliced onto the existing cable because:
Splicing cable together increases the likelihood that water may enter the cable and cause shorting, corrosion, and some other potential issues, which in turn can cause measurement issues.
Because of the potential issues, do not splice any sensor cable without first contacting Campbell Scientific to discuss the sensor in detail.