My orange cap is missing. Do I need to have the cap on to ensure equilibration?

No. Each Rapid RH® Smart Sensor isolates the measuring environment from the outside air using a 2-stage redundancy isolation ring system. As the Smart Sensor is “seated” within the hole, the first stage is a vertical ring on the lowest portion of the Smart Sensor that seals the bottom angle of the drilled hole. At right angles to that, the second stage ring seals off the sidewall of the concrete hole just above the first stage. Equilibration is assured. However, always replace a missing cap to protect the Smart Sensor and minimize debris from getting into the housing when installed on a job site.

See tip number 5 on this video: