Electrical Engineering

🔍

Electrical Engineering

What is a PID controller and what do the proportional, integral, and derivative terms represent?

by EE-Expert in Advanced Control System asked 5 months ago

What is a PID controller and what do the proportional, integral, and derivative terms represent?

Next ⇨Next ⇨⇦ Previous ⇦ Previous

Related questions

in Energy and Environment

What is the fundamental difference between Greenhouse Gases (GHGs) like carbon dioxide and Criteria Air Pollutants like sulfur dioxide, and why do they require different mitigation strategies even though they often come from the same source, such as a power plant?

What is the fundamental difference between Greenhouse Gases (GHGs) like carbon dioxide and Criteria Air Pollutants like sulfur dioxide, and why do they require different mitigation strategies even though they often come from the same source, such as a power plant?
Answer : The fundamental difference lies in their **mechanism of harm** and the **scale of their impact**. Greenhouse gases cause a **global, long-term** problem by altering the Earth's ... compliance with local air quality laws but still be a significant environmental concern from a climate perspective....

X

Full Screen Image

Electrical Engineering

Loading products...

in Utilization Of Electrical Energy

What is the difference between electrical Power (kW) and electrical Energy (kWh), and why do industrial consumers get penalized for having a low Power Factor even if their energy consumption remains the same?

What is the difference between electrical Power (kW) and electrical Energy (kWh), and why do industrial consumers get penalized for having a low Power Factor even if their energy consumption remains the same?
Answer : This question touches on the fundamental economic and technical aspects of utilizing electrical energy. The answer lies in understanding what you are billed for versus what the utility company must actually ... strain on the grid, minimizes energy losses, and frees up capacity for other customers....

X

Full Screen Image

Electrical Engineering

Loading products...

in Applied Mathematics II

Why is the Fourier Series—the ability to represent a complex periodic function as a sum of simple sine and cosine waves—considered one of the most powerful tools in applied mathematics and engineering?

Why is the Fourier Series—the ability to represent a complex periodic function as a sum of simple sine and cosine waves—considered one of the most powerful tools in applied mathematics and engineering?
Answer : The power of the Fourier Series lies in its ability to transform a problem from the often-complex **time domain** into the much simpler and more intuitive **frequency domain**. It acts like a ... ) is impossible. The sharp corners, which rely on the highest frequencies, will always get rounded off....

X

Full Screen Image

Electrical Engineering

Loading products...

in Microwave Engineering & Radar System

Why are microwave frequencies overwhelmingly preferred for radar systems, and what fundamental trade-off does the choice of a specific microwave frequency (e.g., S-band vs. X-band) represent for a radar's performance?

Why are microwave frequencies overwhelmingly preferred for radar systems, and what fundamental trade-off does the choice of a specific microwave frequency (e.g., S-band vs. X-band) represent for a radar's performance?
Answer : The use of microwaves is not arbitrary; they occupy a "sweet spot" in the electromagnetic spectrum that provides the best balance of physical properties for detecting and ranging objects. ... provides the required resolution for the mission, thereby maximizing its all-weather performance and range....

X

Full Screen Image

Electrical Engineering

Loading products...

in Basics of Civil and Mechanical Engineering

What is the difference between stress and strain in a mechanical component?

What is the difference between stress and strain in a mechanical component?

X

Full Screen Image

Electrical Engineering

Loading products...

in Electrical Distribution System

What is the difference between a radial and a ring main electrical distribution system?

What is the difference between a radial and a ring main electrical distribution system?

X

Full Screen Image

Electrical Engineering

Loading products...

in Control System

What is the difference between an open-loop and a closed-loop control system?

What is the difference between an open-loop and a closed-loop control system?

X

Full Screen Image

Electrical Engineering

Loading products...

in Signal & Systems

What is the difference between an analog signal and a digital signal?

What is the difference between an analog signal and a digital signal?

X

Full Screen Image

Electrical Engineering

Loading products...

in Microwave Engineering & Radar System

What is the basic principle behind how a RADAR system detects an object's range and velocity?

What is the basic principle behind how a RADAR system detects an object's range and velocity?

X

Full Screen Image

Electrical Engineering

Loading products...

in Digital Electronics And Microcontroller Applications

What is the difference between a microprocessor and a microcontroller?

What is the difference between a microprocessor and a microcontroller?

X

Full Screen Image

Electrical Engineering

Loading products...

in Elements Of Electronics

What is the difference between a diode and a transistor?

What is the difference between a diode and a transistor?

X

Full Screen Image

Electrical Engineering

Loading products...

in Applied Physics Lab

In a Hall Effect experiment, a voltage is measured perpendicular to both the current flow and the magnetic field. What is the physical origin of this "Hall Voltage," and what two crucial properties of a semiconductor material can be determined by measuring it?

In a Hall Effect experiment, a voltage is measured perpendicular to both the current flow and the magnetic field. What is the physical origin of this "Hall Voltage," and what two crucial properties of a semiconductor material can be determined by measuring it?
Answer : The physical origin of the Hall Voltage is the **Lorentz force** acting on charge carriers as they move through a magnetic field. This simple experiment is profoundly important because it ... **carrier concentration `n`**, a fundamental parameter that dictates the material's electrical properties....

X

Full Screen Image

Electrical Engineering

Loading products...

in Basics of Civil and Mechanical Engineering

From a fundamental engineering mechanics perspective, what is the primary difference between a beam and a shaft, given that both are often long, slender components used in structural and mechanical systems?

From a fundamental engineering mechanics perspective, what is the primary difference between a beam and a shaft, given that both are often long, slender components used in structural and mechanical systems?
Answer : The primary difference lies in the **type of load they are designed to resist** and, consequently, the **purpose they serve**. A **beam** is designed to resist **bending loads**, while a ... it supports. In such cases, engineers must analyze the **combined stresses** from both bending and torsion....

X

Full Screen Image

Electrical Engineering

Loading products...

in Engineering Graphics

What is Orthographic Projection, and what is the fundamental principle that governs the alignment of the standard views (Front, Top, and Right Side) on a 2D engineering drawing?

What is Orthographic Projection, and what is the fundamental principle that governs the alignment of the standard views (Front, Top, and Right Side) on a 2D engineering drawing?
Answer : **Orthographic Projection** is the primary method used in engineering to represent a three-dimensional object on a two-dimensional surface. The core idea is to look at the object from ... the exact 3D object it represents, making it the unambiguous foundation for manufacturing and construction....

X

Full Screen Image

Electrical Engineering

Loading products...

in Applied Physics

From a physics perspective, what makes a semiconductor like silicon fundamentally different from a conductor like copper or an insulator like glass, and how is this difference exploited to create the essential electronic component, the diode?

From a physics perspective, what makes a semiconductor like silicon fundamentally different from a conductor like copper or an insulator like glass, and how is this difference exploited to create the essential electronic component, the diode?
Answer : The fundamental difference lies in the **electron energy band structure** of the materials, specifically the size of the **band gap**. This unique property of semiconductors allows us to precisely ... and off at will is the foundation of all digital logic and the entire modern electronics industry....

X

Full Screen Image

Electrical Engineering

Loading products...

in Object Oriented Programming Using C++

In C++, what is the fundamental problem that the virtual keyword solves when working with inheritance and pointers, and what is the practical difference in behavior when a base class function is declared with versus without it?

In C++, what is the fundamental problem that the virtual keyword solves when working with inheritance and pointers, and what is the practical difference in behavior when a base class function is declared with versus without it?
Answer : The `virtual` keyword solves the critical problem of **static vs. dynamic binding**, enabling **runtime polymorphism**, which is arguably the most powerful feature of Object-Oriented Programming. In simple terms, `virtual` ... NOTE: No 'virtual' keyword here void draw() { std::cout ...

X

Full Screen Image

Electrical Engineering

Loading products...

in Metrology And Measurement

In metrology, what is the fundamental difference between accuracy and precision, and why is it possible—and often dangerous—for a measurement to be highly precise but not accurate?

In metrology, what is the fundamental difference between accuracy and precision, and why is it possible—and often dangerous—for a measurement to be highly precise but not accurate?
Answer : The fundamental difference is that **accuracy** describes the closeness of a measurement to the true value, while **precision** describes the closeness of repeated measurements to each ... . Understanding that a measurement can be consistently wrong is a foundational principle of metrology....

X

Full Screen Image

Electrical Engineering

Loading products...

in Electronic Materials & Components

What is the fundamental difference in the physical mechanism and material structure between a Light Emitting Diode (LED) and a Laser Diode, given that both are semiconductor p-n junction devices that convert electricity into light?

What is the fundamental difference in the physical mechanism and material structure between a Light Emitting Diode (LED) and a Laser Diode, given that both are semiconductor p-n junction devices that convert electricity into light?
Answer : The difference lies in the nature of the photon emission process they utilize and the physical structure required to support that process. An LED relies on **Spontaneous Emission** to produce incoherent light, ... data | Fiber optics, barcode scanners, laser pointers, Blu-ray/DVD players |...

X

Full Screen Image

Electrical Engineering

Loading products...

in Mobile & Wireless Communication

What is the multipath fading problem in wireless communication, and how does the Orthogonal Frequency-Division Multiplexing (OFDM) modulation scheme elegantly solve this problem, which was a major limitation for previous generations of mobile technology?

What is the multipath fading problem in wireless communication, and how does the Orthogonal Frequency-Division Multiplexing (OFDM) modulation scheme elegantly solve this problem, which was a major limitation for previous generations of mobile technology?
Answer : This question addresses the single most challenging physical problem in mobile communication and the ingenious solution that underpins virtually all modern broadband wireless standards. --- ### **Part 1: The Problem - Multipath Fading and ... **4G LTE, 5G NR, and modern Wi-Fi (Wi-Fi 4/5/6/7)**....

X

Full Screen Image

Electrical Engineering

Loading products...

in IoT Applications

In designing an IoT application, what are the key trade-offs between processing data in the Cloud versus at the Edge, and can you provide a real-world example where each approach is clearly superior?

In designing an IoT application, what are the key trade-offs between processing data in the Cloud versus at the Edge, and can you provide a real-world example where each approach is clearly superior?
Answer : This question addresses the fundamental architectural choice of "where the thinking happens" in an IoT system. The decision between Cloud and Edge computing directly impacts an application's ... data analytics, and centralized device management. This combination provides the best of both worlds....

X

Full Screen Image

Electrical Engineering

Loading products...

in Fundamentals Of Power Electronics

What is the main difference between a rectifier and an inverter in power electronics?

What is the main difference between a rectifier and an inverter in power electronics?
Answer : A rectifier converts AC (Alternating Current) → DC (Direct Current). It is used in power supplies, battery charging, and DC motor drives. Example: diode bridge rectifier. An inverter converts DC ... , wind), UPS systems, and variable-frequency drives. Example: PWM (Pulse Width Modulated) inverter....

X

Full Screen Image

Electrical Engineering

Loading products...

in Elements Of Electronics

What is the difference between a diode and a transistor in electronics?

What is the difference between a diode and a transistor in electronics?
Answer : A diode is a two-terminal device that allows current to flow in only one direction. It is mainly used for rectification (converting AC to DC), voltage regulation, and protection ... input current/voltage, making it essential in signal amplification, digital logic circuits, and power control....

X

Full Screen Image

Electrical Engineering

Loading products...

in Basic Science

What is the difference between a fundamental quantity and a derived quantity? Provide two examples of each.

What is the difference between a fundamental quantity and a derived quantity? Provide two examples of each.
Answer : ### The Core Difference In simple terms, **fundamental quantities** are the basic building blocks of measurement. They are independent of each other and cannot be expressed in terms of other physical quantities. Think of them as the ... ** ($m^2$), **Speed** (m/s), **Force** (Newton or kg·m/s²) |...

X

Full Screen Image

Electrical Engineering

Loading products...

in Current Electricity

Six lead-acid type of secondary cells each of emf 2.0 V and internal resistance 0.015 Ohm are joined in series to provide a supply to a resistance of 8.5 Ohm . What is the current drawn from the supply and its terminal voltage?

Six lead-acid type of secondary cells each of emf 2.0 V and internal resistance 0.015 Ohm are joined in series to provide a supply to a resistance of 8.5 Ohm . What is the current drawn from the supply and its terminal voltage?
Answer : ### Given Data: * Number of cells, **n = 6** * EMF of each cell, **E_cell = 2.0 V** * Internal resistance of each cell, **r_cell = 0.015 Ω** * External resistance (load), **R = 8.5 Ω ... The current drawn from the supply is **1.40 A**. * The terminal voltage of the supply is **11.9 V**....

X

Full Screen Image

Electrical Engineering

Loading products...

in Current Electricity

A storage battery of emf 8.0 V and internal resistance 0.5 Ohm is being charged by a 120 V DC supply using a series resistor of 15.5 Ohm . What is the terminal voltage of the battery during charging? What is the purpose of having a series resistor in the charging circuit?

A storage battery of emf 8.0 V and internal resistance 0.5 Ohm is being charged by a 120 V DC supply using a series resistor of 15.5 Ohm . What is the terminal voltage of the battery during charging? What is the purpose of having a series resistor in the charging circuit?
Answer : ### Given Data: * Electromotive force (emf) of the battery, $E = 8.0 \text{ V}$ * Internal resistance of the battery, $r = 0.5 \text{ } \Omega$ * DC supply voltage, $V_{supply} = ... to a much safer and more manageable **7.0 A**, protecting both the battery and the power supply from damage....

X

Full Screen Image

Electrical Engineering

Loading products...

in Current Electricity

A battery of emf 10 V and internal resistance 3 Ohm is connected to a resistor. If the current in the circuit is 0.5 A, what is the resistance of the resistor? What is the terminal voltage of the battery when the circuit is closed?

A battery of emf 10 V and internal resistance 3 Ohm is connected to a resistor. If the current in the circuit is 0.5 A, what is the resistance of the resistor? What is the terminal voltage of the battery when the circuit is closed?
Answer : ### Given Information: * **EMF of the battery (E):** 10 V * **Internal resistance (r):** 3 Ω * **Current in the circuit (I):** 0.5 A --- ### 1. What is the resistance of the ... text{V}$ Both methods give the same result. **Answer:** The terminal voltage of the battery is **8.5 V**....

X

Full Screen Image

Electrical Engineering

Loading products...

in Current Electricity

Three identical cells, each of emf. 2V and unknown internal resistance are connected in parallel. This combination is connected to a 5 ohm resistor. If the terminal voltage across the cell is 1.5 volt. What is the internal resistance of each cell? Hence define the internal resistance of a cell?

Three identical cells, each of emf. 2V and unknown internal resistance are connected in parallel. This combination is connected to a 5 ohm resistor. If the terminal voltage across the cell is 1.5 volt. What is the internal resistance of each cell? Hence define the internal resistance of a cell?
Answer : ### Part 1: Calculating the Internal Resistance Here's how we can find the internal resistance of each cell. **Given Data:** * Electromotive force (EMF) of each cell, E = 2 V * Number of identical cells ... . * **I** is the current flowing from the cell. * **r** is the internal resistance....

X

Full Screen Image

Electrical Engineering

Loading products...

in Current Electricity

In a potentiometer arrangement, a cell of emf 1.25V gives a balance point at 35.0cm length of the wire. If the cell is replaced by another cell and the balance point shifts to 63.0cm , what is the emf of the second cell?

In a potentiometer arrangement, a cell of emf 1.25V gives a balance point at 35.0cm length of the wire. If the cell is replaced by another cell and the balance point shifts to 63.0cm , what is the emf of the second cell?
Answer : ### Principle The working principle of a potentiometer is that the potential drop across any portion of a wire of uniform cross-section is directly proportional to the length of that portion, provided a constant current flows ... 2.25 V** ### Answer The EMF of the second cell is **2.25 V**....

X

Full Screen Image

Electrical Engineering

Loading products...

in Current Electricity

A Carbon resistor has three strips of red colour and a gold strip. What is the value of the resistor? What is its tolerance?

A Carbon resistor has three strips of red colour and a gold strip. What is the value of the resistor? What is its tolerance?
Answer : The value of a carbon resistor is determined by the standard resistor color code system. For a 4-band resistor: * **Band 1:** First significant digit * **Band 2:** Second significant ... a new resistor with these color bands will have an actual resistance somewhere between 2090 Ω and 2310 Ω....

X

Full Screen Image

Electrical Engineering

Loading products...

in Current Electricity

Two wires A and B are of the same metal and of same length have their areas of cross section in the ratio 2:1 if the same potential difference is applied across each wire in turn, what will be the ratio of current flowing in A & B ?

Two wires A and B are of the same metal and of same length have their areas of cross section in the ratio 2:1 if the same potential difference is applied across each wire in turn, what will be the ratio of current flowing in A & B ?
Answer : The ratio of the current flowing in wire A to wire B is **2:1**. --- ### Detailed Explanation Let's break down the problem using the relevant physics principles. #### 1. List the Given ... resistance, which is wire A. Our result confirms this: the current in A is twice the current in B....

X

Full Screen Image

Electrical Engineering

Loading products...

in Current Electricity

What is drift velocity? Derive expression for drift velocity of electrons in a good conductor in terms of relaxation time of electrons?

What is drift velocity? Derive expression for drift velocity of electrons in a good conductor in terms of relaxation time of electrons?
Answer : --- ### Part 1: What is Drift Velocity? In a metallic conductor (like a copper wire), the outer electrons of the atoms are not bound to individual atoms. They are free to move throughout the entire volume of ... field. * The magnitude of the drift velocity is given by: $v_d = \frac{e\tau}{m}E$....

X

Full Screen Image

Electrical Engineering

Loading products...

in Advance Power Electronics

What are the fundamental limitations of traditional "hard-switched" PWM converters, and how do resonant or "soft-switching" techniques like Zero Voltage Switching (ZVS) and Zero Current Switching (ZCS) overcome these limitations to achieve higher efficiency and power density?

What are the fundamental limitations of traditional "hard-switched" PWM converters, and how do resonant or "soft-switching" techniques like Zero Voltage Switching (ZVS) and Zero Current Switching (ZCS) overcome these limitations to achieve higher efficiency and power density?
Answer : This question addresses the critical challenge of **switching loss**, the primary barrier to increasing the operating frequency, and therefore the power density, of modern power converters. ** ... state-of-the-art applications like server power supplies, EV chargers, and renewable energy inverters....

X

Full Screen Image

Electrical Engineering

Loading products...

in Electrical And Electronic Measurement

How does a digital multimeter measure voltage, and what is its basic working principle?

How does a digital multimeter measure voltage, and what is its basic working principle?

X

Full Screen Image

Electrical Engineering

Loading products...

in Embedded System

What is a Real-Time Operating System (RTOS), and why is it frequently used in embedded systems instead of a general-purpose operating system like Linux or Windows?

What is a Real-Time Operating System (RTOS), and why is it frequently used in embedded systems instead of a general-purpose operating system like Linux or Windows?
Answer : The answer lies in one critical concept: **determinism**. While a general-purpose OS is designed for high throughput and fairness, an RTOS is designed for predictability and meeting strict timing deadlines. ... system where **failing to complete a task on time is considered a total system failure.**...

X

Full Screen Image

Electrical Engineering

Loading products...

in Computer Aided Drawing And Simulation

Why is a 3D CAD model more than just a "digital drawing" when used for engineering simulation, and what key information must be added to this geometric model to perform a meaningful analysis like a stress test?

Why is a 3D CAD model more than just a "digital drawing" when used for engineering simulation, and what key information must be added to this geometric model to perform a meaningful analysis like a stress test?
Answer : This question highlights the fundamental difference between defining an object's **form** (CAD) and predicting its **function** (Simulation). While a 3D CAD model is the essential starting point, it ... gradients, enabling them to identify and fix design flaws before a single piece of metal is cut....

X

Full Screen Image

Electrical Engineering

Loading products...

in Engineering Graphics

What is the difference between isometric and orthographic projections in technical drawing?

What is the difference between isometric and orthographic projections in technical drawing?

X

Full Screen Image

Electrical Engineering

Loading products...

in Engineering Economics & Management

What is the difference between fixed costs and variable costs in an engineering project?

What is the difference between fixed costs and variable costs in an engineering project?

X

Full Screen Image

Electrical Engineering

Loading products...

in Energy and Environment

What is the greenhouse effect and how does it contribute to global warming?

What is the greenhouse effect and how does it contribute to global warming?

X

Full Screen Image

Electrical Engineering

Loading products...

in Metrology And Measurement

What is the difference between accuracy and precision in measurement?

What is the difference between accuracy and precision in measurement?

X

Full Screen Image

Electrical Engineering

Loading products...

in mathematics-i

What is the Fundamental Theorem of Calculus, and why is it considered "fundamental" to the study of calculus?

What is the Fundamental Theorem of Calculus, and why is it considered "fundamental" to the study of calculus?
Answer : The Fundamental Theorem of Calculus is the central pillar that connects the two main branches of calculus: **differentiation** and **integration**. In essence, it rigorously proves ... This relationship is the foundation for countless applications in physics, engineering, economics, and statistics....

X

Full Screen Image

Electrical Engineering

Loading products...

in Energy Conservation & Green Building

In the context of green building and energy conservation, what is the fundamental difference between R-Value and U-Value, and why is one typically used for individual materials like insulation, while the other is used for complex assemblies like windows?

In the context of green building and energy conservation, what is the fundamental difference between R-Value and U-Value, and why is one typically used for individual materials like insulation, while the other is used for complex assemblies like windows?
Answer : The fundamental difference is that they are mathematical reciprocals of each other, measuring opposite things: **R-Value measures resistance to heat flow**, while **U-Value measures the rate ... envelope that conserves energy by keeping heat inside during the winter and outside during the summer....

X

Full Screen Image

Electrical Engineering

Loading products...

in Environmental Education And Sustainability

What is the difference between renewable and non-renewable resources, and why is the shift toward renewables important for sustainability?

What is the difference between renewable and non-renewable resources, and why is the shift toward renewables important for sustainability?
Answer : Renewable resources are naturally replenished on a human timescale, such as solar, wind, hydro, and biomass energy. Non-renewable resources like coal, oil, and natural gas are finite ... that future generations have access to reliable energy sources without depleting the planet's natural reserves....

X

Full Screen Image

Electrical Engineering

Loading products...

in Electrical And Electronic Measurement

What is the difference between analog and digital instruments in electrical measurement?

What is the difference between analog and digital instruments in electrical measurement?
Answer : Analog instruments use a continuously moving pointer or needle to represent the measured quantity. Example: moving-coil ammeter, analog voltmeter. They are simple and give a visual trend but have lower ... and can store or process data, but they may be costlier and require power supply/electronics....

X

Full Screen Image

Electrical Engineering

Loading products...

in Fundamental Of Electrical Engineering

What is the difference between AC (Alternating Current) and DC (Direct Current)?

What is the difference between AC (Alternating Current) and DC (Direct Current)?
Answer : Direct Current (DC): The flow of electric charge is in one constant direction. Sources include batteries, solar cells, and DC power supplies. It is mainly used in electronics, charging, ... because it can be easily transformed to higher or lower voltages using transformers, reducing energy loss....

X

Full Screen Image

Electrical Engineering

Loading products...

in Current Electricity

Three resistors 1 Ohm , 2 Ohm and 3 Ohm are combined in series. What is the total resistance of the combination?

Three resistors 1 Ohm , 2 Ohm and 3 Ohm are combined in series. What is the total resistance of the combination?
Answer : When resistors are combined in series, the total resistance is the sum of the individual resistances. The formula is: R_total = R1 + R2 + R3 Given the values: * R1 = 1 Ω * R2 = 2 Ω * R3 = 3 Ω ... = 1 Ω + 2 Ω + 3 Ω = 6 Ω So, the total resistance of the combination is **6 Ohms**....

X

Full Screen Image

Electrical Engineering

Loading products...

in Electronics Engineering

What is the function of a capacitor in an electronic circuit?

What is the function of a capacitor in an electronic circuit?
Answer : To store electric energy when the circuit is closed and release the energy when circuit is opened ...

X

Full Screen Image

Electrical Engineering

Loading products...

in Flexible AC Transmission System

What is the role of a FACTS device like a STATCOM in a power transmission system?

What is the role of a FACTS device like a STATCOM in a power transmission system?

X

Full Screen Image

Electrical Engineering

Loading products...

in Switch Gear & Protection

What is the primary function of a circuit breaker in an electrical system?

What is the primary function of a circuit breaker in an electrical system?
Answer : It Cuts the power off in any fault in the circuit such as overloading to protect appliances....

X

Full Screen Image

Electrical Engineering

Loading products...

in Microprocessor & Microcontroller

What is the function of the Arithmetic Logic Unit (ALU) in a microprocessor?

What is the function of the Arithmetic Logic Unit (ALU) in a microprocessor?

X

Full Screen Image

Electrical Engineering

Loading products...

in Power System

What is the purpose of a substation in an electrical power grid?

What is the purpose of a substation in an electrical power grid?

X

Full Screen Image

Electrical Engineering

Loading products...

...