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Edition 3
Rev G
Section 4
4-27
DERIVED VARIABLE FUNCTION
To simplify formulas or make them easier to read, various letters or abbreviations are used for the inputs, such as
A, B, X, or TEMP. During configuration, a descriptive prompt will appear on line 1, as specified by "PROMPT:" for
each input, while the source of the input is selected via a choice of inputs on line 2.
A Derived Variable can have up to five value inputs, one actuator input, and a reset actuator. The description for
each Derived Variable Function identifies its corresponding inputs. Input choices set to NONE USED will evaluate
to zero unless specified otherwise.
Unless specifically stated, it is assumed that all values have been converted to the proper scale and units before
being used as an input. In some cases, temperatures will be automatically converted to the required units as
specified. Should a divide by zero be attempted, the result will be set to 99999.
1. SUB, MUL, DIV, EXP, LOG 10, LOG e, POWER 10, POWER e
INPUT 1: A PROMPT: DVxx INPUT A
INPUT 2: B PROMPT: DVxx INPUT B
ACTUATOR: n/a
RESET: n/a
OUTPUT: = A-B for SUB - Subtraction
= A*B for MUL - Multiplication
= A/B for DIV - Division
= A**B for EXP - Exponent
= B*LOG(A) for LOG 10 - Log to the Base 10
= B*LN (A) for LOG e - Natural Log
= B*10**A for POWER 10 - Power of 10
= B*e**A for POWER e - Power of e
For LOG 10, LOG e, POWER 10, and POWER e, if INPUT 2 is "NOT USED" then B=1.
2. LIN - LINEAR
INPUT 1: X PROMPT: DVxx INPUT X
INPUT 2: A PROMPT: DVxx INPUT A
INPUT 3: B PROMPT: DVxx INPUT B
ACTUATOR: n/a
RESET: n/a
OUTPUT: = A*X+B
3. CUSTOM CURVE 1, through CUSTOM CURVE 4
INPUT 1: X PROMPT: DVxx INPUT
ACTUATOR: n/a
RESET: n/a
OUTPUT: = Extrapolated result using the corresponding CUSTOM CURVE.
NOTES: The OUTPUT will be limited by the output values of the first and last POINT PAIR entries.