Correcting Discrepancies in Historian/VantagePoint Tags: Adjusting PLC Values for Accurate Calculations

Question:

I have noticed that there are discrepancies in the tags in Historian/VantagePoint, with values off by one decimal point. I have observed that the HMI displays the correct number by multiplying the PLC tag by 0.1. All links in Historian are already set up to the PLC tags, so I am exploring options for an easy solution. Is it possible to incorporate an equation to adjust the tag from the PLC within Historian or VantagePoint? Alternatively, I may consider adding additional rungs/branches to the PLC to generate tags with the necessary calculations already implemented. However, this process, along with retargeting all Historian tags, will require significant effort.

Top Replies

VantagePoint offers a feature called Calculated Tags, allowing users to create and calculate values using mathematical expressions. It is important to note the limit on the number of Calculated Tags that can be created within the system.

Operaghost explained that VantagePoint offers a feature for creating Calculated Tags, allowing users to perform mathematical operations to obtain the desired value. While there is a limit to the number of Calculated Tags allowed, the exact number is unknown. This information was exactly what I needed after spending all day searching for a solution to my issue. Despite trying various terms, I had not thought to search for "calculated tags" until now.

You might consider leveraging Historian's calculated tag feature, which can be used to implement the equation you mentioned. By setting up a calculated tag that multiplies the original PLC tag value by 0.1, you should be able to see the correct values in Historian. This somewhat easier approach could save you the effort of retargeting all tags and modifying your PLC program. Just bear in mind that calculated tags will use more system resources, so make sure your system performance can accommodate this.

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Frequently Asked Questions (FAQ)

FAQ: 1. Why are there discrepancies in the tags in Historian/VantagePoint, with values off by one decimal point?

Answer: Answer: The discrepancies could be due to different scaling factors used in displaying data between the PLC and the HMI, leading to the need for adjustments in the tags.

FAQ: 2. Is it possible to adjust the tag values within Historian or VantagePoint to match the correct numbers displayed by the HMI?

Answer: Answer: Yes, it may be possible to incorporate an equation within Historian or VantagePoint to adjust the tag values from the PLC, ensuring accurate calculations.

FAQ: 3. What are the considerations when deciding between adjusting tags within Historian/VantagePoint or implementing calculations directly in the PLC?

Answer: Answer: Deciding whether to adjust tags in Historian/VantagePoint or modify the PLC directly involves assessing factors such as ease of implementation, maintenance efforts, and the impact on existing systems.

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