Specify integer and real I/O tags

You must assign I/O integer and real tags a set of attributes that characterize numerical data sent between the InTouch application and external processes.

The InTouch HMI normalizes raw input data from a PLC. The figure below shows the process of clamping raw I/O data values and then scaling them to engineering units that can be shown from an InTouch application.

I/O integer and real tags include attributes that set minimum and maximum limits for raw input data sent by the PLC. The InTouch HMI clamps I/O values that are below or above the raw value range. Clamping reassigns values outside of the range to the minimum or maximum raw values.

I/O integer and real tags include attributes that scale clamped raw values within a range of engineering units. Minimum and maximum engineering unit attributes set the upper and lower boundaries of the scaled values.

When you define integer and real I/O tags, you specify the type of conversion to scale raw values when calculating engineering units. You can select Linear or Square Root.

For linear scaling, the result is calculated using linear interpolation between the minimum and maximum end points. The algorithm for linear scaling of input is:

EUValue = (RawValue - MinRaw) * ((MaxEU - MinEU) / (MaxRaw - MinRaw)) + MinEU

The algorithm for linear scaling of output is:

RawValue = (EUValue - MinEU) * ((MaxRaw - MinRaw) / (MaxEU - MinEU)) + MinRaw

For square root scaling, the minimum and maximum raw values are used for interpolation. This is useful for scaling inputs from nonlinear devices like pressure transducers. The algorithm for square root scaling of input is:

EUValue = sqrt(RawValue - MinRaw) * ((MaxEU - MinEU) / sqrt(MaxRaw - MinRaw)) + MinEU

The algorithm for square root scaling of output is:

RawValue = square((EUValue - MinEU) * (sqrt(MaxRaw – MinRaw) / (MaxEU -MinEU))) + MinRaw

Define integer and real I/O tags

1. Open the Tagname Dictionary and assign a name for a new tag.

2. Assign I/O integer or I/O real as the type of tag from the Tag Types dialog box. The detail portion of the Tagname Dictionary dialog box appears.

   

3. Do the following:

   • In the Initial Value box, type the integer or real number associated with the tag when the application starts.

     The application does not write this initial value to the external process.

   • In the Min EU box, type the minimum engineering unit for the tag.

   • In the Max EU box, type the maximum engineering unit for the tag.

   • In the Min Raw box, type the minimum value of the low clamp for raw I/O integer or real numbers.

   • In the Max Raw box, type the maximum value of the high clamp for raw I/O integer or real numbers.

   • In the Eng Units box, type the label to use for the tag's engineering units.

   • Select Linear or Square Root as the type of conversion to scale raw values when calculating engineering units.

4. Save your changes to the tag.