Example 3.

A Two-Step Thermostat Control

The previous two examples use a single fan. In this example, we use the temperature to trigger two fans in a staged manner. The second fan is assigned to output “fan2.” Following the approach of Example 2, we use two set points, “setpoint1” and “setpoint2.”

title "example 3a. two-step thermostat"

input iT1;

output oFan1, oFan2;

parameter pSetPoint1, pSetPoint2;

if(iT1< pSetPoint1)

{

oFan1=0;

oFan2=0;

}

else

{

if(iT1< pSetPoint2)

{

oFan1=1;

oFan2=0;

}

else

{

oFan1=1;

oFan2=1;

}

}

This is an example of a nested conditional statement. The else-clause of the first conditional statement is another conditional statement with its own condition, action and else-clause. Observe the use of the curly brackets to delineate each compound statement , be it an action or an else-clause.

It is possible to implement the same logic without nested conditional statement. Consider the following.

title "example 3b. two-step thermostat"

input t1;

output fan1, fan2;

parameter setpoint1, setpoint2;

if(t1<setpoint1)

{

fan1=0;

fan2=0;

}

if( (t1>=setpoint1) && (t1<setpoint2) )

{

fan1=1;

fan2=0;

}

if(t1>=setpoint2)

{

fan1=1;

fan2=1;

}

The burden of nested conditional statements is removed, but only with the added expense of a more complicated conditional statement. The condition above is made up of two sub conditions, namely t1>=setpoint1, and t1<setpoint2. These two conditions are AND-ed using the Boolean operator “&&.” Refer to the section “Script Syntax” for more information about Boolean operators.

Recall the argument in Example 1 about efficiency. The current program may also be streamlined. Consider the following.

title "example 3c. two-step thermostat"

input t1;

output fan1, fan2;

parameter setpoint1, setpoint2;

fan1=(t1>=setpoint1);

fan2=(t1>=setpoint2);

Not only does this version render nested conditional statements unnecessary, but also steers clear of complicated conditions. Of course, it is not always possible to simplify the instructions, as it was the case here. In such cases, the earlier examples may provide some guidelines to implementing programs for complex applications.

Also see : Programming, Program Examples, Script Syntax

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