Resolving slow tag address updates within InTouch
For various reasons reading address values from PLC’s within InTouch (or any other SCADA application for that matter!) can be fairly slow unless configured correctly to ensure all connected devices respond quickly to I/O changes.
With InTouch SCADA and an Omron PLC as an example, the following adjustments can be made to increase the update rates of Tag values.
1. PLC: Depending on the PLC used most PLC’s assign a certain amount of time within processing cycle for secondary peripheral device processing. This could be for an Ethernet or serial communications card that the InTouch SCADA data access driver is using for communication. There is usually a default amount of time assigned for peripheral device processing, which (in the case of the Omron PLC’s) can be adjusted through the PLC programming software (CX-One for Omron). This setting can be adjusted within the Main PLC setting section, which is usually an amount of milliseconds to allow for secondary device processing. This value should be increased to allow enough time for PLC ladder logic and also the communications card(s) to process quickly. The Omron PLC’s are set to 4ms by default for secondary device processing, which can be adjusted (depending on the size of the PLC program) to 200 to 300ms for a dramatic increase in communications speed to the SCADA application.
2. The device group within the data access driver should have its update time interval (ms) reduced from default if required. Reducing this from 1000ms to 250ms will increase the update rate by 4.
3. Depending on the driver used for accessing the data within InTouch, the DA server, I/O server , or OPC server can be adjusted for each topic to update more frequently by reducing the amount of time between updates. i.e. 1000ms to 250ms to increase the update speed by 4.
4. If there are topics within the data access driver which aren’t being used, remove them. Extra load on these items for processing could slow down the updates for other topics that are being used.
5. Make sure that there no unused I/O tags within the InTouch Application. Reducing the amount of tags will make the overall tagname dictionary items more responsive. This can be done by using the delete tags function from the “Special” menu. Important: Make sure you backup your application first before deleting tags from the tagname dictionary!