URL Scanner

Help Contents

Introduction

The URL Scanner Tag :

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

Uses of URL Scanner Tag include:

Retrieve forecast data from an Internet weather service and write forecast values to I/O Data Point Tags.
Retrieve a data file from an FTP server and then write extracted data to I/O Data Point Tags.

For an example of retrieving weather data see Fernhill SCADA Connection to OpenWeatherMap.

Configuration Properties

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

Property	Type	Version	Description
ReadInterval	TIME	3.33	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	3.33	The offset added to the ReadInterval to get the actual read time. See Interval and Offset for information on how timed activities are scheduled.
ReadTimeout	TIME	3.33	The maximum time allowed to read the file from the URL.
URL	WSTRING	3.33	The URL of the file to read.
URLOptions	WSTRING	3.39	The URL Options to apply to the file transfer.
FileType	USINT	3.33	The format of the data file. 0 = CSV, 1 = JSON.
AlarmSeverity	UINT	3.33	The severity of the alarm raised when the data file cannot be read.
Password	WSTRING	3.33	An optional password value to send in the request. Note: The password value is encrypted and not stored as plain text.
UserName	WSTRING	3.33	An optional username to send in the request to read the file.

URL Property

The URL configuration property tells the driver where to locate the data file on the Internet or Intranet. The following example shows how to retrieve a file using the HTTP protocol:

http://example.com/folder/data-file.csv

You can also use the https protocol for secure transfer:

https://example.com/folder/data-file.csv

You can also use FTP:

ftp://example.com/folder/data-file.csv

Note: Use the UserName and Password configuration properties to set the login credentials for the FTP service.

With some remote services the URL is not fixed. For example, the URL 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 URL property of the URL Scanner Tag.
A TagRefresh Function Block to trigger a scan of the URL Scanner Tag.

FileType

The FileType configuration property tells the driver the format of the Data File. These formats are supported:

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

UserName & Password Properties

The service providing the file may require authentication. Use the UserName and Password configuration properties to provide the login credentials for the service.

Data Properties

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

Further Information

Fernhill SCADA Connection to OpenWeatherMap

To learn how to retrieve data from the OpenWeatherMap service.

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 URL Scanner Tag.

I/O Digital Data Point Tag

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

I/O String Data Point Tag

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

I/O Word Data Point Tag

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

Data File Driver

For an overview of the Data File Driver.

Glossary

For the meaning of terms used in Fernhill SCADA.