The top cover and/or door of a chart recorder is the portion of the device that is placed on the outside, housing the remaining fragile components. The top cover that does not hinge open like a door is seen in both classical and paperless variants of chart recorders. It is simple in construction and merely acts as a shell to the rest of the device. The top cover is placed around the outer edges of the chart recorder and covers all pieces of the device apart from the chart and arm. Paperless chart recorders that resemble computer monitors are protected by their own variation of top cover that similarly cannot be opened.
Chart recorder doors are similar in their functionality to the top cover, but they possess one defining difference: they allow the user to access the innerworkings of the chart recorder. Door covers visually reflect a plastic suitcase of sorts that protects the chart recorder while possessing a clasp on the side for user accessibility. Some top doors look like their unopenable variant, but upon further observation, a small knob or alternative apparatus is provided to open the door.
Both variations add a layer of protection to the inner mechanisms of the chart recorder. Depending on the material and thickness of the top cover/doors, both provide some level of protection from damage caused by the user that occur through accidental droppings or bumping. Damaged top covers and doors can be replaced but may require technical assistance depending upon the specific model of chart recorder being used.