CIMPLICITYStep 3.2. Configure the Conversion Type for a Device Point
CIMPLICITY supports the following types of Engineering Unit (EU) conversions for device analog points:
- None
- Linear conversion.
- Custom conversion.
None (no conversion)
When None (no device conversion) is checked, the active measurement system is used.
Example
A point's value represents degrees in Fahrenheit.
The Unit field is blank.
The active measurement system uses Metric units.
However, there is no conversion from degrees in Fahrenheit to degrees in Centigrade during runtime.
Linear Conversion
- Linear configuration
- Linear conversion formula
Linear configuration
When Linear is checked, fields are as follows.
| Raw values | Low | Two valid raw values. |
| High | ||
| Converted values | Low | Engineering unit values that correspond to the low and high raw values. |
| High |
Linear conversion formula
These four values calculate the linear conversion for the point.
The conversion formula is:
Where
| EU value | = | the Engineering Units value |
| RL | = | Low raw value |
| RH | = | High raw value |
| CL | = | Low conversion value |
| CH | = | High conversion value |
| Raw value | = | the value read from the device. |
The inverse of this expression converts set point values that are entered by users to raw values. The raw values can be downloaded to the device.
Custom Conversion
- Custom conversion configuration.
- Valid operations.
- Expression processor interpretation.
Custom Configuration
When Custom is checked conversion fields are as follows.
| Forward | Converts the raw data to engineering units. |
| Use the placeholder %P to indicate the point value in the expression. %P is the raw value of the point. | |
| Reverse | Converts set point values from engineering units to raw data. |
| Use the placeholder %P to indicate the point value in the expression. %P is the engineering units value of the point. |
Valid Operations
Forward and Reverse operations use the functions that are available in the Expression Editor .
Example
A conversion calls for the raw data to be divided by 10.0 then multiplied by 2.5.
The Forward expressions is (%P/10.0)*2.5
The Reverse expression is
(%P/2.5)*10.0
Expression processor interpretation
- The numeric operands you use in the Forward expression are assumed to be integers unless you include decimal points in them. Once the expression processor sees an operand with a decimal point, it will process the rest of the expression using floating-point arithmetic.
- A conversion that inverts the sign, (e.g. a FWD Conversion = %P(-1) and REV Conversion = %P(-1)) will not work correctly if you configure a set point, range or alarm limits
Example
A conversion that calls for the raw data to be divided by 2, then multiplied by 10.
The raw value for the point is 3.
You could enter any one of the following expressions. However, the Expression Processor interprets each expression differently, as follows:
| Expression | Result |
|---|---|
| Because integer arithmetic was used throughout, the result is an integer: | |
(%P/2)*10
|
(3/2)*10 = (1)*10 = 10
|
| Because integer arithmetic was used in the first operation of these two expressions, the operation (3/2) gives the result 1 instead of 1.5: | |
(%P/2)*10.0
|
(3/2)*10.0 = (1)*10.0 = 10.0
|
| Because (3/2.0) is processed using floating point arithmetic, the rest of the expression will be processed using floating point arithmetic, even thought 10 is entered as an integer: | |
(%P/2.0)*10
|
(
3/2.0)*10 = (1.5)*10 = 15.0
|
| Because (3/2.0) is processed using floating-point arithmetic, the rest of the expression will be processed using floating-point arithmetic: | |
(%P/2.0)*10.0
|
(3/2.0)*10.0 = (1.5)*10.0 = 15.0 |