A historian that stored every sample of every tag forever would drown in data, most of it meaningless jitter. Deadband compression is how historians keep the archive small and meaningful: they store a value only when it changes by more than an amount you consider significant, and skip the noise in between. This guide explains deadband compression, the swinging-door algorithm behind good historians, and how to set it without losing real events.
What Is Deadband Compression? in one line: Deadband compression is a technique historians use to reduce stored data by only recording a value when it changes by more than a defined threshold (the deadband). Small, insignificant fluctuations within the deadband are discarded, so the archive keeps meaningful changes while dropping noise.
The simplest form is exception deadband: the historian compares each new reading to the last stored value and archives the new one only if it differs by more than the deadband. This is easy and effective for flat signals, but it can be crude on a ramping signal - a steadily rising level triggers a stored point at every deadband step, and a slow drift can be missed if each step stays just under the threshold.
Better historians use a swinging-door algorithm (the technique made famous by a traditional process historian). Instead of comparing to the last stored point, swinging door checks whether the intermediate points can be reconstructed by a straight line within the deadband. As long as every skipped point lies within a tolerance corridor of a line drawn from the last stored point, they are dropped; when a point falls outside the corridor, the previous point is archived and a new corridor begins. This captures trends and slopes with far fewer stored points than simple deadband, while guaranteeing the reconstructed value never deviates from the real one by more than the deadband.
The deadband is usually set per tag, in engineering units or as a percentage of range, and it directly trades storage against fidelity. Too wide and you erase real movement - a small but meaningful pressure excursion vanishes into the archive as a straight line. Too narrow and you store instrument noise, bloating the historian and slowing queries with no analytical benefit.
A sound approach is to base the deadband on instrument accuracy and process significance: set it just above the sensor's noise floor and below the smallest change you would actually act on. Many teams also distinguish a collection or exception deadband (what the field device or interface reports) from an archive compression deadband (what the historian keeps), so noise is filtered close to the source and only meaningful changes are both sent and stored.
Deadband compression is lossy by design - it discards data you have declared insignificant - so it must be configured deliberately, especially for tags used in custody transfer, allocation, or regulatory reporting, where you may want tighter deadbands or full-resolution collection. For most monitoring tags, though, sensible compression is what makes years of history affordable and trends fast to load.
Note the close relationship to report by exception: RBE applies a deadband at the field device to save bandwidth, while historian compression applies a deadband at the archive to save storage - the same idea at two points in the pipeline. Merobix stores time-series history for every monitored tag with configurable compression, so operators keep meaningful history at full fidelity without archiving instrument noise.
It is a method that stores a tag's value only when it changes by more than a set threshold (the deadband), discarding smaller fluctuations as noise. This shrinks the archive to meaningful changes, so years of history stay affordable to store and fast to query.
Swinging door is a compression method that keeps a point only when the values in between cannot be reconstructed by a straight line within the deadband tolerance. It captures ramps and trends with very few stored points while guaranteeing the reconstructed signal stays within the deadband of the real one. It is the classic historian compression technique.
Set it just above the instrument's noise floor and below the smallest change you would actually act on, based on process significance and sensor accuracy. Too wide erases real events; too narrow stores noise and bloats the archive. Use tighter deadbands for custody-transfer or regulatory tags where full fidelity matters.
Merobix reads your field devices into a cloud SCADA - the real thing behind these terms, live in days from any browser.