From the Office of Bishop Perez:
Liturgical Catechesis Notes – Perpetual Adoration vs Perpetual Exposition
It has been observed that some parishes in the diocese seem to be confused about the differences between Perpetual Adoration of the Blessed Sacrament and Perpetual Exposition of the Blessed Sacrament. All parishes should be open to the faithful for some period of time each day for adoration before the Blessed Sacrament reserved in the tabernacle (canon 937); however, this is not the same as exposition. Some key points regarding exposition:
• Exposition takes place with a monstrance or ciborium placed on the altar; exposition does not take place within an open tabernacle.
• Exposition should be attended by at least two adorers at all times. There must absolutely never be periods when the Blessed Sacrament is exposed in a monstrance or ciborium on the altar and there is no one present for adoration. (Perpetual Exposition of the Blessed Sacrament)
• Exposition may not be casually or temporarily interrupted – if interruption must take place, it must be at previously scheduled times, and these may not be scheduled more than twice in a 24-hour period. (Order for the Solemn Exposition of the Holy Eucharist, no. 12)
• Covering the monstrance or ciborium with a cloth or drape to temporarily interrupt exposition is not foreseen by the Church, and is prohibited. (Thirty-One Questions on Adoration of the Blessed Sacrament: A Resource of the Bishops’ Committee on the Liturgy (2004), no. 24)
For more information, please consult the USCCB website on Perpetual Exposition, the USCCB handbook Thirty-One Questions on Adoration of the Blessed Sacrament, or the LTP publication Guide to Celebrating: Worship of the Eucharist Outside Mass.