5.2.4.10        Scaling Type

Applies to Analog type parameters and tags.  Scaling type specifies how to convert data read from the field device to a number meaningful to users and operators. Specifies how to re-scale input from device into actual Engineering Units.  Parameter Scaling Type defines the initial Scaling Type for Tags and BLOCK:PARAMETERS created using this parameter.  Parameter Scaling Type can save time and typing or enforce a standard if this parameter will be used in a predictable way to create Tags or Blocks.

Scaling works with SPAN LOW and SPAN HIGH.  Many automation devices supply data a raw form. For example, many 12-bit IO devices supply all values as an integer between 0 and 4096. For example, the appropriate scaling type, SPAN HI and SPAN LO could be used to rescale t0 -4096 to 0 to 14.7 psig.

Valid Scaling Types are driver dependant. A pull down list shows valid scaling types for this device.  Typical scaling types include:

No Scale

For a value not requiring scaling or one that will be scaled prior to reaching the computer. Will display raw value read from device and ignore the Span High and Low.

Scale 0-100 Input to Span

This will convert values between 0 and 100 to specified Low and High Span (SPAN LOW and SPAN HIGH). Fits input of 0 - 100 into SPANLO - SPANHI. This assumes the input is a value between 0 and 100.

If input exceeds 100, then the value of the tag will exceed SPAN HIGH.  Selecting this conversion, and specifying SPANLO = 0 and SPANHI = 1000 will effectively multiply the input by 10.  The conversion algorithm is approximately:

OUTPUT = (SPANHI - SPANLO) / 100 * INPUT + SPANLO

Linear scale MX+B

This will convert input using the classic equation for a line (i.e. linear input) where:

OUTPUT = M * INPUT + B

SCALING FACTOR 1 = M, the slope of the line.

SCALING FACTOR 2 = B, the intercept of the line with the x -axis.

Scale Defined Input H/L to Span

This will convert values between INPUT LOW and INPUT HIGH to specified Low and High Span (SPAN LOW and SPAN HIGH). This assumes the input is a value between INPUT LOW and INPUT HIGH.

If input exceeds INPUT HIGH, then the value of the tag will exceed SPAN HIGH.  Selecting this conversion, and specifying SPANLO = 0 and SPANHI = 1000, INPUT LOW = 0 and INPUT HIGH = 100 will effectively multiply the input by 10.  The conversion algorithm is approximately:

OUTPUT = (SPANHI - SPANLO) / (INHI - INLO) * (INPUT - INLO) + SPANLO

SCALING FACTOR 1 = INPUT HIGH.

SCALING FACTOR 2 = INPUT LOW.

Scale 12-Bit Input to span

Commonly used to read IO Multiplexors or IO cards that use the industry standard of 12 bit accuracy.   This conversion reads only the first 12 bits of the word then re-ranges the value to fit the Low and high span (SPAN LOW and SPAN HIGH).  It converts an input that ranges between 0 and 4096 to the specified SPAN LOW and SPAN HIGH for the bock.

Scale 0-100 Square Root Input

Commonly used to convert Flow from differential Flow meters (i.e. convert 0 -100 inches H20 to GPM). This will convert the square root of values between 0 and 100 to specified Low and High Span (SPAN LOW and SPAN HIGH). Fits square root of input of 0 - 100 into SPANLO - SPANHI. This assumes the input is a value between 0 and 100 (hence 0 -100 %).

The conversion algorithm is approximately:

OUTPUT = (SPANHI - SPANLO) / 100 * SQUARE ROOT(INPUT) + SPANLO