Sensor and Actuator Basics for PCB Design

January 29, 2020 Cadence PCB Solutions

People walking into a mall-complex with a motion sensor door

 

I supposed the adage that ‘the apple doesn’t fall far from the tree’ is true to a certain extent. At 7, my son showed immense interest in technology-driven mechanisms. As he passed through an automated-sliding door, it occurs to him for the first time that it seems magical. 

It took me a while to explain that there’s no one hiding in a booth with a remote control. To pacify his curiosity, I went into a lecture of sensors and actuators, hoping they made some sense to a child’s mind. 

As you may have guessed, the concept of automating a sliding door with electronics seems beyond a child’s comprehension as he remained convinced of manual intervention. But if you’re venturing into PCB design, you ought to be familiar with the workings of sensors and actuators. 

Sensors And Actuators Basics

In simple words, sensors are electronics that convert real word parameters into electrical signals. A sensor can be in the form of a simple switch or could be a more complex barometric pressure sensor. Over the past decades, the use of sensors has grown exponentially to provide better user experience in consumer electronics. 

Actuators are the opposite of sensors. Instead of sensing real-time variables, actuators turn energy input into physical movements. You’ll find actuators used in applications like robots, HVAC, water pumps or a typical automatic sliding door.  

 

A type of motion sensor available for IoT home networks

An infrared motion sensor for home alarm. 

 

Different Types of Sensors and Actuators 

The electronics industry is flooded with different types and shapes of sensors. Here are some common ones that you’re likely to come across.

  • IR Sensor - measures distance by gauging the distance of IR reflection. 

  • Ultrasonic sensor - produces ultrasonic waves and detecting the echo to determine obstacles along its path. 

  • Temperature sensor - uses the thermodynamic principle to convert changes in temperature into electrical signals. 

  • Touch sensor - convert physical contact by using capacitive, resistive or inductive sensing into electrical pulses. 

  • Pressure sensor - turns physical diaphragm deflection into electrical signals. 

 

Chances are, you’re surrounded by some of these sensors in your daily life. Your smartphone is obviously equipped with touch sensors, while the air conditioner sets the right temperature with a temperature sensor. 

 

Actuators are categorized according to the source of their input energy.

  • Pneumatic actuators - turn compressed air into physical motion.

  • Hydraulic actuators - use pressured liquid to generate torque and motion.

  • Electric actuators  - generates physical force with electricity 

  • Mechanical actuators - turns rotary motion into linear motion. 

 

It’s obvious that only electric actuators are directly powered by an electronics circuit. Common types of electric actuators are AC motors, servo motors, and stepper motors. Some hybrid actuators have electric controls built-in alongside the existing elements. 

Designing With Sensors And Actuators

While it’s true that both sensors and actuators are represented by the familiar electrical signals, you shouldn’t take the design process for granted. Systems that utilize sensors and actuators for critical applications require a flawless design.

 

Actuators within an industrial heating system

Pneumatic actuators are used in a steam heating system. 

 

For example, the actuators could be controlling high-pressure air compressors and there’s no room for errors. The same goes for humidity sensors installed in surgery rooms in hospitals. The role of PCB designers is vital to ensure hardware-level mistakes are non-existence.

1. Choosing The Right Part

When designing applications involving sensors and actuators, you could be collaborating with projects or application engineers. While you have limited control over the physical aspects of the parts, you’ll need to be attentive to the electrical characteristics of the sensors and actuators.

For example, temperature sensors may provide raw analog signals or a serial communication interface. Both will result in different hardware and software design strategies. The choice of driving a stepper motor or AC motor means including different types of driver circuits.

2. Electrical Interference Prevention

As mentioned, electronics that incorporate sensors and actuators involves mechanical movement based on the parametric input. In actual deployment, the PCB may experience higher electrical noise exposure compared to lab testing.

You’ll need to ensure proper EMI prevention techniques are applied. Sensor inputs should be kept cleared from high-speed signals and proper ground separations must be done on the PCB. The accuracy of the sensor signal is crucial to maintain the proper functioning of the system. 

3. Fail-Safe Condition

When you’re dealing with moving parts, you need to consider the fail-safe condition of the system. For example, an industrial air dryer system requires only certain valves to be opened at any one time. Get that wrong and you’ll have a catastrophic accident with the high-pressure air movement. 

As a PCB designer, you’ll need to be clear of the workings of the system and the fail-safe condition of the moving mechanisms. Choosing an NC or NO relay to control airflow valves is a huge difference in maintaining safety when system power fails.

Using a PCB design software with signal analysis capability greatly minimizes the risk when designing with sensors and actuators. OrCAD is the tool you need to manage both your design’s layout needs and any collaborative processes between mechanical and analysis teams when working with signal-intensive designs. 

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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