ACD – Archive compression using Delta criterion

Block SymbolLicensing group: STANDARD

Function Description
The ACD (Archive Compression using Delta criterion) block is meant for storing compressed analog signals to archives using archive events.

The main idea is to store the input signal u only when it changes significantly. The interval between two samples is in the range $⟨$ tmin,tmax $⟩$ seconds (rounded to the nearest multiple of the sampling period). A constant input signal is stored every tmax seconds while rapidly changing signal is stored every tmin seconds. When the execution of the block is started, the first input value is stored. This value will be referred to as u0 in the latter. The rules for storing the following samples are given by the delta and TR input signals.

The list of archives for storing is specified by the arc parameter, e.g. 1,3..5,8. The event will be stored in all specified archives. Each archiving block must have a unique event identification code in the archive given by the id parameter. For more information about these parameters see the introduction of chapter 10.

For $TR = off$ the condition $| u - u0 | > delta$ is checked. If it holds and the last stored sample occurred more than tmin seconds ago, the value of input u is stored and u0=u is set. If the condition is fulfilled sooner than tmin seconds after the last stored value, the error output E is set to 1 and the first value following the tmin interval is stored. At that time the output E is set back to 0 and the whole procedure is repeated.

For TR=onthe input signal values are compared to a signal with compensated trend. The condition for storing the signal is the same as in the previous case.

The following figure shows the archiving process for both cases: a) TR=off, b) TR=on. The stored samples are marked by the symbol $\times$ .

This block does not propagate the signal quality. More information can be found in the 1.4 section.

Input

u	Signal to compress and store	Double (F64)
delta	Threshold for storing the signal $↓$ 0.0 $↑$ 1e+10	Double (F64)

Parameter

acls	Archive class (data type) $⊙$ 8	Byte (U8)
	1 .... Bool 2 .... Byte (U8) 3 .... Short (I16) 4 .... Long (I32) 5 .... Word (U16) 6 .... DWord (U32) 7 .... Float (F32) 8 .... Double (F64) 10 ... Large (I64)
arc	List of archives to write the events to	Word (U16)
id	Unique archive item ID $⊙$ 1	Word (U16)
tmin	The shortest interval between two samples [s] $↓$ 0.001 $↑$ 1000000.0 $⊙$ 1.0	Double (F64)
tmax	The longest interval between two samples [s] $↓$ 1.0 $↑$ 1000000.0 $⊙$ 1000.0	Double (F64)
TR	Trend evaluation $⊙$ on	Bool
	off .. Disabled on ... Enabled
Desc	Event description string $⊙$ Value Description	String

Output

y	The last value stored in the archive	Double (F64)
E	Error indicator	Bool
	off .. No error on ... An error occurred

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