Writing Scaled OPC tag from Memory tag

Ignition
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1

Hi,

I have a quick question regarding tags, and scaling.

We have a system where we have a SPEED tag and a SPEED_SET tag coming from a PLC.

The SPEED tag, which is read-only and comes in as 2000-5000, which I can scale to 40-100% fine.

The issue comes with the SPEED_SET tag. It is expecting 2000-5000. We have a slider that is in the range 40-100(%).

So my question is, how could I map 40-100 -> 2000-5000 -> Write to SPEED_SET (OPC Tag)?

My current solution is to have the SPEED_SET bind to the slider (40-100), then create a derived tag, which scales the SPEED_SET to 2000-5000, then use an OnValueChanged script to write this to the OPC tag.

Is this the best solution, or am I not seeing something?

Note: I can't bind the derived tag to the slider, as this means the scale goes from 2000-5000, and I cannot do the scaling in the slider itself, as this seems to disable the 'bi-directional' property.

It seems that the derived tag is the only way to have scaling on read and write independently, but this is not enough.

2

Every OPC tag can have linear scaling applied to it, which is fully bidirectional. Use this on both tags, so the underlying 2000-5000 values are completely hidden. Do be sure to set the tag type float.

4

image

Like this? I have set it to a memory tag for now.

The slider is a 100% and it is showing a value of 2.0

5

Looks like you have raw and scaled backward.

6

Your value source is Memory. The scaling operations only apply to OPC tags.

7

I can see it changing now, I did not realise that it only applies to OPC values.

Also, when changing the slider now, there is a green box stating, good write pending. Is there anyway I can not show this to the user?