Basics instruction

Now let’s examine some of the basic instruction is greater detail to see more about what each one does.

Load

The load instruction is a normally open contact. It is sometimes also called examine if on. The symbol for a load instruction is shown below.

This is used when an input signal is needed to be present for the symbol to turn on. When the physical inputs on we can say that the instruction is true. We examine the input is physically on then symbol is on. An on condition is also referred to as a logic 1 state.

This symbol normally can be used for internal inputs, external inputs and external outputs. Remember that internal relays don’t physically exist. They are simulated relays.

LoadBar

The Loadbar instruction is normally closed contacts. It is sometimes also called LoadNot or examine if closed. The symbol for a loadbar instruction is shown below.

This is used when an input signal does not need to be present for the symbol to turn on. When the physical input is off we can say that the instruction is true. We examine the input for an off signal. If the input physically off then the symbol is on. An off condition is also referred to as logic 0 state.

This symbol normally can be used for internal inputs, external inputs and sometimes external output contacts. Remember again that internal relays don’t physically exist. They are simulated relays. It is the exact composite of the load instruction.