PLC Guides

# What is the Signal?

Written by

#### 1. What is the Signal?

A signal is a physical quantity that contains information or data that can travel long distances and isolates information. Usually signals will be sent as a function of a specific distribution graph.

#### 2. How to classify signals?

There will be many ways for us to classify signals, but based on attributes, we can divide them into small categories such as:

2.1 Discrete signals – continuous signals:

+ A time-discrete signal is a signal that can only be identified on a discrete set of times (usually a discrete set of times). In mathematical form, discrete signals with real (or complex) values can be considered as a corresponding linking function from the natural set to the real set (or complex).

+ A continuous signal in terms of time is a signal of real (or complex) value determined at any time in a certain period of time, the most common case being an infinite period of time.

2.2 Digital signal – analog signal:

+ Digital signal: A form of discrete signals according to their amplitude. This type of signal is only shown in two levels 0 and 1 corresponding to the voltage value 0 and 5V. This is one of the signals that is widely used in today’s signaling devices such as network cables, usb, rs232, connection ports, …

+ Analog signal: A type of continuous signal over time. They have graphs that show the amplitude, phase and frequency of the current changing continuously over time. The analog signal will usually have a sinusoidal function graph. And this is also a type of signal commonly used on the market today as in applications related to sound waves, brain impulses, light waves, …

Because these two types of signals are used quite a lot today, plc247.com will give a comparison table. Through it you can easily distinguish them so that they can be applied to everyday tasks more easily.

2.3 Energy signal – power signal:

+ Energy signal is a type of signal with a defined energy level. Often signals are triangular pulses.

+ Power signal is a signal form having a defined average power level. And has a sinusoidal amplitude.

#### 3. Analog signals and industrial applications

Currently, most self-uniforming industrial systems use Analog signals. The reason is because it is easier to control. As shown above, signals such as temperature, humidity, pressure are analog signals, cannot use digital signals because there is no temperature of only 0癈 or 1癈. Must use equipment analog to measure and represent them.

In factories and industrial parks use a variety of sensors that measure temperature, pressure, humidity, pH, etc. Therefore, analogue signal conversion devices will use 4-20mA electrical signals, or 0-10V to represent the change of these signals. Therefore, there are currently two types of industry standard analog signals: current 4-20mA, 0-20mA and voltage 0-10V, 0-5V
Although currently in some other areas, analog signals have gradually been replaced by digital but in industry, analog signals are still used a lot and are indispensable.