Deadbands and Scaling with Memory Tags in LabVIEW DSC
Primary Software: LabVIEW Modules>>LabVIEW DSC Module
Primary Software Version: 7.1
Primary Software Fixed Version: 7.1
Secondary Software: N/A
Problem: Are there any special concerns when setting scales and deadbands for memory tags in LV DSC?
Solution: Yes, memory tags are different from other tags when it comes to setting scales and deadbands.
- Scaling involves converting between one set of "physical" units to some other units. For example, 0 -10 volts in the physical world can correspond to 1- 150 psi in the program. With memory tags, by definition, there is no outside or physical world, so there is no generalized way of applying scaling to memory tags. This can be a problem, however, if you are connecting a physical quantity to a memory tag. Say you have a device which is reading data in degrees Celsius and you write to a memory tag. You are using this memory tag somewhere else (reading from it) and you want degrees Fahrenheit. One way of handling all these conversions would be to switch units before you write or use a subVI for the conversion.
- Given that scaling doesn't directly apply to memory tags, the "Method of Scaling" option for a memory tag in the Tag Configuration Editor (TCE) is grayed out. Normally you are able to choose "Linear" or "Square Root" as the method of scaling.
- By setting the scaling units to "none", DSC will not perform any unit scaling on the tag. This applies to all tags, not just memory tags.
- You can still modify the range of the values that he tag accepts. Changing the scale will affect the impact of the update deadband.
- The update deadband is applied to the memory tag to determine which values are actually logged to the tag. Values that don’t have a higher change than the specified deadband won’t be logged to the tag. The alarm deadband will also be applied to the memory tag to determine the tag’s status.
- The value displayed on the user interface reflects scaling, update deadband, and alarm deadband.
For more information about deadbands and DSC in general, please see the following related links.
Related Links:
KnowledgeBase [2RIFA7Q7]: What is a Deadband? What Types of Deadbands Exist? How are Deadbands Configured in OPC and the LabVIEW DSC Module?
Product Manual: LabVIEW Datalogging and Supervisory Control Module Developer Manual
Attachments:
Report Date: 01/14/2005
Last Updated: 01/11/2006
Document ID: 3HDE2360
