csmstr - Omega Engineering

WRITING EXPRESSIONS
COMPARING VALUES
value by a floating-point value, the integer will be converted to floating-point before the
division is carried out. However, there will be some situations where you want to force a
conversion to take place.
For example, suppose you are adding together three integers that represent the levels in three
tanks, and then dividing the total by the tank count to obtain the average level. If you use an
expression such as (Tank1+Tank2+Tank3)/3 then your result may not be as accurate as you
demand, as the division will take place using integer math, and the average will not contain
any decimal places. To force Crimson to evaluate the result using floating-point math, the
simplest technique is to change the 3 to 3.0, thereby forcing Crimson to convert the sum to
floating-point before the division is performed. A slightly more complex technique is to use
syntax such as float(Tank1+Tank2+Tank3)/3. This invokes what is known as a “type cast”
on the term in parentheses, manually converting it to floating-point.
Type casts may also be used to convert a floating-point value to an integer value, perhaps
deliberately giving-up some precision from an intermediate value before storing it in a PLC
register. For example, the expression int(cos(Theta)*100) will calculate the cosine of an
angle, multiply this value by 100 using floating-point math, and then convert it to an integer,
dropping any digits after the decimal place.
COMPARING VALUES
You will quite often find that you wish to compare the value of one data with another, and
make a decision based on the result. For example, you may wish to define a flag formula to
show when a tank exceeds a particular value, or you may wish to use an if statement in a
program to execute some code when a motor reaches its desired speed. The following
comparison operators are provided…
OPERATOR PRIORITY EXAMPLE
Equal To Group 7 Data == 100
Not Equal To Group 7 Data != 100
Greater Than Group 6 Data > 100
Greater Than or Equal To Group 6 Data >= 100
Less Than Group 6 Data < 100
Less Than or Equal To Group 6 Data