File Scanner Tag

Introduction

The File Scanner Tag represents an external data file.

The File Scanner Tag:

Reads the data file on demand or at a regular interval.
Extracts data from the file.
Writes the extracted data to associated I/O Data Point Tags.

Configuration Properties

The File Tag supports the configuration properties of the Alarm Tag plus these properties:

Property	Type	Version	Description
ReadInterval	TIME	1.6	The interval between each read. An interval value of zero (T#0s) disables periodic query execution. See Interval and Offset for information on how timed activities are scheduled.
ReadOffset	TIME	1.6	The offset added to the ReadInterval to get the actual read time. See Interval and Offset for information on how timed activities are scheduled.
FileName	WSTRING	1.6	The name of the data file to read.
FileType	USINT	3.33	The format of the data file. 0 = CSV, 1 = JSON.
RetryAttempts	UINT	1.6	The maximum number of consecutive file open failures before a file access attempt is considered failed.
RetryInterval	TIME	1.6	The interval between consecutive file open attempts.
AlarmSeverity	UINT	1.6	The severity of the alarm raised when all attempts to read the data file have failed.
UpdateFileName	WSTRING	1.6	The name of the optional CSV update file. Write requests to tags are appended to this file. If write operations are not required, this field can be left blank.

FileName Property

With some files the file name is not fixed. For example, the file name may require a formatted date component based on the current date and time. In this situation consider using a IEC 61131-3 Program Tag with the following:

The FORMAT_DATE_TIME() Function to format a date and time to the required format.
A ConfigureTag Function Block to make a configuration change to the FileName property of the File Scanner Tag.
A TagRefresh Function Block to trigger a scan of the File Scanner Tag.

FileType Property

The FileType configuration property defines the format of the external data file. These data file formats are supported:

Value	Format	Description
0	CSV	Comma separated variables conforming to RFC 4180.
1	JSON	JavaScript Object Notation conforming to ECMA-404.

RetryAttempts & RetryInterval Properties

The driver expects the Data File and Update File to be occasionally not accessible. This might be caused an external program is accessing these file(s). To avoid false alarms, the File Scanner will try up to RetryAttempts to open the external file before reporting an error. The delay between retry attempts is configured by the RetryInterval property.

If the driver cannot read the Data File after using all the retry attempts, an alarm will be raised. If the driver cannot access the Update File after using all of the retry attempts, the write request(s) will be failed.

When Fernhill SCADA reads the Data file, it will be temporarily locked to prevent updates. Any external program generating the Data File should be written to handle the file being locked.

UpdateFileName Property

The Data File driver can support write operations using an update file. When a write request is made on a tag, a new line is appended to the update file. The format of the new line is:

TagName=Value

The tag name is taken from the WriteTagName property of the tag. To complete the write request, an external program should periodically read and delete the CSV update file.

Data Properties

The File Scanner supports the data properties of the Alarm Tag, plus these additional data properties:

Property	Type	Description
FileState	UINT	A code indicating the state of the external data File. The value 15 shows the data file was successfully read. Other values indicate an error. The ErrorMessage property may give additional information.
ErrorMessage	WSTRING	An error message providing additional information.
ReadTimer	TimerStatus	The status of the read timer.

The FileState property can be used to diagnose problems with the data file:

ServerState	Description
0	Initial state before the driver has started
1	The driver was unable to open the data file
15	The data file was successfully read

Tag Commands

The File Scanner supports the tag commands of the Alarm Tag plus these tag commands:

Tag Command	Version	Description
Refresh	1.6	Requests an immediate read of the tags associated with this File Scanner.

Note: Event triggered data reads (from the Refresh Tag Command) and periodic data reads (defined by the ReadInterval property) are independent. You can use the Refresh Tag Command, or the ReadInterval property, or both to determine when the tags are read.

Relationships to Other Tag Types

The File Scanner Tag builds on the features of these tag types:

Further Information

Interval and Offset

To learn how activities are scheduled using Interval and Offset.

I/O Analog Data Point Tag

To learn about the I/O Analog Data Point Tag that can be associated with the File Scanner Tag.

I/O Digital Data Point Tag

To learn about the I/O Digital Data Point Tag that can be associated with the File Scanner Tag.

I/O String Data Point Tag

To learn about the I/O String Data Point Tag that can be associated with the File Scanner Tag.

I/O Word Data Point Tag

To learn about the I/O Word Data Point Tag that can be associated with the File Scanner Tag.

I/O Double Word Data Point Tag

To learn about the I/O Double Word Data Point Tag that can be associated with the File Scanner Tag.

Data File Driver

For an overview of the Data File Driver.

Glossary

For the meaning of terms used in Fernhill SCADA.