External Item Data Validation

This feature makes it possible to perform various data validations of data values on Apis external items before making use of the data. An alarm is triggered when a data validation fails. The alarm will be logged in the system log, but it is also possible to send it out as an e-mail notification. When a validation fails, the invalid data may be substituted according to different rules.

The data-validation is performed when the value of the item connected as the external item changes. When an item fails a data-validation check, the quality of the item will include some Apis specific quality information, see Apis Vendor Specific Item Qualities for details.

Data-validation methods

Apis supports the following data validation methods:

Data validation method

Abbreviation

Value*

Description

Related item attribute(s)

None

None / 0

0

 

 

Bad quality

BQ / 1

1

Validation fails when the quality of the item becomes bad

 

Range

R /

2

Validation fails when the value of the item violates a range check

DvHiRange, DvLoRange

Rate of change

ROC

4

Validation fails when the value of the item changes to fast

DvMaxRoc

Watchdog

WD

8

Validation fails when the value of the item stops updating

DvWdTime

Difference

DF

16

Validation fails when the difference of the value of the item compared to the value of an other item is too big

DvCompareValue, DvCompareItem

Absolute difference

ADF

32

Validation fails when the absolute value of the difference of the value of the item compared to the value of an other item is too big

DvCompareValue, DvCompareItem

SPC

SPC

64

Any of the supported SPC tests, see Apis Online SPC.

DvSPCTest, DvSPCLCL, DvSPCUCL

*) When using File-add, the values of the desired DV methods must be OR-ed together. Eg: R | ROC = 6

The following item attributes are used in data validation:

ID

Name

Description

Type

5670

DvMethod

The method that decides which data validation tests to use. Any combination the following is possible: None, BQ, R, ROC, WD, DF, ADF, SPC.

2 byte unsigned integer

5672

DvHiRange

The high limit for DV range check.

8 byte real

5673

DvLoRange

The low limit for DV range check.

8 byte real

5674

DvMaxRoc

The maximum rate of change for DV rate of change check.

8 byte real

5676

DvWdTime

The time limit in seconds for DV watch dog check.

8 byte real

5677

DvCompareItem

An external item used by data-validation methods DF and/or ADF, when comparing values.

 

5678

DvCompareValue

The value to compare the difference with, when using data-validation methods DF and/or ADF

8 byte real

5680

DvSPCUCL

The upper control limit in SPC.

8 byte real

5681

DvSPCLCL

The lower control limit in SPC.

8 byte real

5682

DvSPCTest

The assignable causes tests to perform (multiple selects possible, e.g. 1;3;4). 1 - 1BEYZA, 2 - 9BEYCENT, 3 - 6INCDEC, 4 - 14ALTUPDO, 5 - 2OF3INZA, 6 - 4OF5INZB, 7 - 15INZC, 8 - 8OUTZC. Test codes explained.

string

5690

DvSubstMethod

The method that decides which data validation substitute value to use. One of the following may be selected:

Name

Meaning

Value

last good

Substitute with last good value when data validation fails

1

InitVal

Substitute with InitVal attribute when data validation fails. If no InitVal is associated with the item, it uses the last good value

2

AltExtItem

Substitute with an alternative external item (DvAltExtItem). If no alternative external item can be obtained, it uses the last good value

3

PassThrough

No substitution occurs, external item is passed through as if no validation failed

4

Follow ROC

Substitute with a value that increases/decreases with a rate of change limitation according to the maximum rate of change (DvMaxRoc).

5

Default

First, value is  substituted after a Follow ROC strategy, if DvMethod specifies ROC.
Then, if DvMethod specifies Range, a range check validation is performed. If Range-chack fails, an AltExtItem substitution  is performed if an DvAltExtItem is specifed.

If none of the above mentioned substitution occurs, the default substitution is last good..

255

2 byte unsigned integer
5691 DvSubstQuality

The quality to use when data validation substitution takes place.  This attribute lets the user control the quality for item values when Data Validation substitution takes place, the quality can be overridden to bad, uncertain or good, by specifying the desired quality using the DvSubstQuality attribute.

The APIS Vendor specific quality bits, telling what violation is broken , will still be added to the quality. I.e. when using Range validation, the quality of the item during a violated state is decided according to the table below, but with Apis Vendor quality range added to the quality.

Name

Meaning

Value

Default

 The quality follows the quality of the source item, with any with Apis Vendor quality violation state added to it.

255
Bad The quality is always set to bad, with any with Apis Vendor quality violation state added to it. 0
Uncertain The quality is always set to uncertain, with any with Apis Vendor quality violation state added to it. 64
Good The quality is always set to good, with any with Apis Vendor quality violation state added to it. 192
unsigned character

5692

DvAltExtItem

An alternative external item to fetch a DV substitute value from. Used when 'DvSubstMethod'='AltExtItem'.

string

Note:  The module property ExtItemCalculationSequence is important in data validation and transfer. It decides whether data validation or data transfer will be performed first in the external item manager. Available values: TransferBeforeValidation, ValidationBeforeTransfer.

Data-validation alarms

Data validation will generate alarms into the Alarms & Event server of Apis, and OPC clients can retrieve these alarms over OPC UA and OPC AE. Further, data-validation alarms & events can be written to an Apis event database, configuration of this is described in Advanced Event Configuration.