A Complete Guide to Potentiometers

Our guide explains what potentiometers are, potentiometer types, pinouts, and how they work in electronic circuits.

A potentiometer is a three-terminal resistor that adjusts voltage by forming an adjustable voltage divider. Also referred to as a "pot," it regulates electric current by varying resistance between its terminals, much like how a resistor functions in a circuit to limit or oppose the flow of current. Potentiometers are passive electronic components widely used in electronic circuits for applications such as adjusting voltage levels, controlling audio volume, and providing user input for various devices.

A potentiometer consists of a resistive element, a wiper (sliding contact), and three terminals. The resistive element is typically made from materials like carbon, cermet, or conductive plastic, each offering different electrical characteristics. As the wiper moves along the resistive element, it changes the resistance between terminals, controlling the circuit's electrical flow.

In circuit diagrams, the potentiometer symbol is a resistor with an arrow pointing toward it, indicating its adjustable resistance capability.

Key Applications of Potentiometers:

• Volume Control: Used in audio devices to adjust sound levels.
• Sensor Calibration: Helps in fine-tuning sensors for precise measurements.
• User Interfaces: Provides adjustable settings in various electronic devices.

By understanding the functionality and applications of potentiometers, you can enhance your designs and improve user experience in your electronic projects.

Potentiometers are constructed with several key components:

• Resistive Element: This is the core of the potentiometer, providing the resistance that can be varied. Common materials include carbon, cermet, and conductive plastic, each with its own characteristics in terms of resistance range, linearity, and temperature stability.
• Wiper (Sliding Contact): The wiper is a movable contact that slides along the resistive element, changing the resistance between the terminals. It is typically made of a conductive material, such as metal or carbon.
• Terminals (Pins or Leads): Potentiometers have three terminals: two fixed terminals connected to the ends of the resistive element and one variable terminal connected to the wiper. These terminals allow the potentiometer to be connected to other components in a circuit.
• Housing & Sealing: The housing protects the internal components of the potentiometer from dust, moisture, and other environmental factors. Some potentiometers also feature sealing to prevent the ingress of contaminants, ensuring reliable operation in harsh environments.
• Rotational Life: This refers to the number of times a potentiometer can be rotated before its performance degrades. It is an important consideration for applications where the potentiometer will be frequently adjusted.

Potentiometers are available in a wide range of resistance values, typically from a few ohms to several megohms. Standard resistance values often follow the E series (e.g., E6, E12, E24), which defines preferred values to cover a wide range with a limited number of components.

Marking codes on potentiometers indicate their resistance value and tolerance. Common formats include:

• Numeric: e.g., 10K for 10 kilohms
• Alpha-numeric: e.g., 103 for 10 kilohms (using the EIA-96 marking code)

Potentiometers can function as either variable resistors or variable voltage dividers:

• Variable Resistor: When used as a variable resistor, only two terminals of the potentiometer are used: one fixed terminal and the wiper terminal. The resistance between these two terminals can be adjusted by moving the wiper.
• Variable Voltage Divider: When used as a voltage divider, all three terminals of the potentiometer are used. The input voltage is applied across the two fixed terminals, and the output voltage is taken from the wiper terminal. The output voltage varies depending on the position of the wiper.

Potentiometer Pinouts

Potentiometers typically have three pins, each with a specific function:

• Pin 1 (Input/Fixed Terminal): This pin is connected to one end of the resistive element and is typically where the input voltage is applied.
• Pin 2 (Wiper/Output): This pin is connected to the wiper and provides the variable output voltage or resistance.
• Pin 3 (Ground/Fixed Terminal): This pin is connected to the other end of the resistive element and is often connected to the ground.

Connecting Potentiometer Pinouts

• As a Voltage Divider: Connect the input voltage across pins 1 and 3, and take the output voltage from pin 2. The position of the wiper determines the output voltage.
• As a Variable Resistor (Rheostat): Connect one end of the circuit to pin 1 and the other end to pin 2. The resistance between these two pins can be adjusted by moving the wiper.

Choosing the right potentiometer is crucial for optimal performance in your electronic circuits. Consider these key factors:

Resistance Range

The resistance range of a potentiometer determines the span of resistance values it can provide. Choose a potentiometer with a resistance range that aligns with your circuit requirements. For example, if your application requires fine-tuning a low-current circuit, a potentiometer with a lower resistance range might be suitable. Conversely, if you need to control higher currents or voltages, a higher resistance range would be necessary.

Power Rating

The power rating of a potentiometer indicates the maximum power it can safely dissipate without overheating or damage. Ensure the potentiometer you choose has a sufficient power rating to handle the expected current and voltage levels in your circuit. Exceeding the power rating can lead to premature failure or even safety hazards.

Material

The material of the resistive element in a potentiometer affects its performance characteristics. Common materials include carbon, cermet, and conductive plastic.

Carbon potentiometers: Cost-effective but may have limited linearity and temperature stability.

Cermet potentiometers: Offer better linearity and temperature stability, making them suitable for more demanding applications.

Conductive plastic potentiometers: Provide excellent linearity and long life but may have higher cost.

Consider the specific requirements of your application when choosing the material.

Tolerance

The tolerance of a potentiometer indicates the permissible deviation from its nominal resistance value. Choose a potentiometer with an appropriate tolerance level based on the required accuracy of your application. For precision applications, a lower tolerance is necessary, while for general-purpose use, a higher tolerance might be acceptable.

Operating Environment Conditions

The operating environment can significantly impact the performance and lifespan of a potentiometer. Consider factors such as temperature, humidity, and exposure to dust or moisture. For industrial settings or harsh environments, choose a potentiometer with a wide operating temperature range and appropriate sealing to protect against contaminants.

Compliance to Australian Standards

Potentiometers used in certain applications in Australia must often comply with specific standards to ensure safety, reliability, and environmental responsibility. Some key standards to consider include:

• AS/NZS 3100: This Australian/New Zealand standard specifies requirements for electrical installations, ensuring the safety of electrical equipment and installations.
• IEC 61000-4-5: This international standard defines the requirements for electromagnetic compatibility (EMC), ensuring that electronic devices can operate without causing interference or being susceptible to interference.
• RoHS and WEEE: These directives restrict the use of hazardous substances in electrical and electronic equipment and promote environmentally responsible disposal.

As a trusted supplier of potentiometers, RS Australia sources our products from reputable brands like TE Connectivity, Bourns and Vishay, ensuring compliance with relevant Australian standards. Enjoy peace of mind knowing you're buying quality products when you shop with us.