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**Home ⇒ Overview Courses ⇒ PLC ⇒ ****Analog and Digital**

### Analog and digital

In general, analog values can take any value within a permissible range. Accordingly, an analog display must also give each value.

Countable elements are used for digital size representation. Digital comes from `digitus` (Latin for finger). For example, a number can be represented by a number of fingers. Well known is the **Abacus**, a sort of hand operated mechanical calculator using beads on rods, first used by Sumerians and Egyptians around 2000 BC.

**Digital values consist of countable elements!**

A numeric display is called a 'digital' display. Measuring instruments with a numerical display are called 'digital measuring instruments'; clocks with a numerical display are called digital clocks.

Note:

Computers and automation systems process electrical signals. One could represent the number 3, for example, by 3 electrical impulses. To represent the number 100,000 one would need 100,000 impulses. This makes no sense - numerical codes are used here.

#### Logical states of binary signals

Binary technology knows signals with two possible states. In other words: These elements are bivalent or binary. Examples of this are easy to find:

First binary state Second binary state

Switch closed Switch open

Pulse present Pulse not present

Voltage high Voltage low

Current flow No current measurable

Since information is processed electronically, it must be represented by binary code. There are certain tolerances for these binary voltage states. The low voltage level is designated L (low); the higher voltage level is designated H (high). The terms "logic 0" and "logic 1" are also frequently used.