Analog Output change by strategy vs by slider gadget


I have a question about an approach to change one analog output using a chart. I use this formula to send a signal to a flow controller with an output 0-100% of the signal.
AO_MFC_Nitrogen_SP = ((SP_Nitrogen_Flowrate + MFC_Nitrogen_Adjust_Increment)/MFC_Nitrogen_Range) *100;

At the same time I have another location where I can use a slider gadget to change AO_MFC_Nitrogen_SP manually for calibration purposes.

if I use the slider to send a 14% of the signal range to the controller, the flow controller reacts appropriately and responds.

Response from the flow controller:

However, if I start the chart that have the formula above the channel registers the same value of 14% but there is no response received from the flow controller.

response from the flow controller

I am wondering, is there a conflict between the slider gadget and the formula that is written in the strategy? Does the gadget take precedent in updating the signal?

Yes, there is a conflict. Both are masters.
Which one wins?
Depends on you.

This is common ‘problem’ and one that comes up pretty often.
You have two inputs to one output. Which one wins?
It depends on the process and the process programmer… and that would be you…

In short, you need to think about which one should be the master and which should be the slave and at what point of the process should each be each.
The forums cant really answer those for you because we don’t know the process as well as you.
But. Think about at what times should the user slider should control the process and at what times should the chart control the process.

Tip, you may want to connect the slider to a variable in the chart and have the chart ‘consider’ when the user slider variable should control the process and when the user slider should be ‘ignored’ and the chart take control and reflect to the slider what the chart is doing.

Tip. Be sure and let the user know when they are in control and when they are not.
ie, your suggestion of a manual/calibration step in the process could be a string/button.

Lets know what you end up doing as its a very important process control question to ‘answer’.


Thank you for your input. I had no idea when i looked at the groov guide that the slider is considered a master as well.
I have generated a temp variable and linked the slider to it, this variable now only send its value to the AO only when the machine is in calibration mode. all other cases the slider gadget doesnt have impact to the AO, and now the channel responds appropriately.

I appreciate your input, this has been really helpful.

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