Temperature sensors typically help us to know how hot or cold something is. We need various electronic gadgets, even for industrial applications. For example, we need it in air conditioners, cars, ovens, and even in your phone or smartwatch. These sensors could be tiny, but they typically perform a crucial task. In this case, designing the temperature sensor PCB is a critical process.
There are various kinds of temperature sensors out there. Each of them has its unique applications. Some are fast, some are strong, and some are very accurate. You must choose the correct sensor type based on your project needs.
When you are building electronics with temperature sensors, it’s also essential to design the PCB carefully. The number of layers, trace width, solder masks, PCB material, and all other factors matter. For high-temperature applications, you must opt for special materials. In this case, working with expert PCB manufacturers can help you ensure the reliability of your gadget.
This article will explain everything about temperature sensor PCB design. It will begin with explaining different types of temperature sensors. Later, it will highlight some of the most crucial factors to consider when designing a temperature sensor PCB.
Understanding Temperature Sensor Types
You might have questions about sensor types. Why do they have lots of varieties? Typically, it depends on various factors and needs. For example, it depends on the accuracy, range, and safety, as well as costs. Each type has its particular efficiencies. Now, the rest is in your hands; select the type based on your needs and budget.
Silicone IC Temperature Sensors
A silicon IC temperature sensor is a common type of temperature sensor. The word “silicon” typically comes from its structure, which is built on a silicon semiconductor chip. It generally comes with three different types.
Logic output sensors typically deliver signals when the temperature reaches its limits. These sensors offer high accuracy (±1°C) when measuring. In addition, it also passes a lower amount of current (600 µA). This makes it suitable for use instead of mechanical switches or for safety controls.
Voltage output sensors, on the other hand, send out an analog value that changes with temperature. Here, the common coefficients of temperature are 6.25 mV/°C, 10 mV/°C, or 19.5 mV/°C. The temperature range is between -40°C and +125 °C. Commonly, they are suitable for control loops and portable devices.
Finally, serial output sensors provide data in digital communication systems. It utilizes an interface such as I²C, SMBus, or SPI standards to display the data. The accuracy rate is significantly lower, typically around ±0.5 °C. This is why the sensor is widely used in computers and consumer electronics.
Thermocouples
Thermocouples are made from two materials. They are temperature sensors that create a voltage. Using two dissimilar wires and connecting them at a junctional point, a voltage is produced. In this case, the voltage varies with the temperature changes. The range of handling temperature is enormous. It can handle temperatures from -200°C to 1800°C. Mainly, the ranges depend on the specific types we use.
Talking about the applications, it includes furnaces, engines, and industrial control. Signal amplification, junction correction, and EMI filtering are key components of thermocouple designs.
RTDs
RTDs (Resistance Temperature Detectors) are a special type of sensor. It detects temperature across resistance in electrical circuits. These resistances are made with metal, usually they are platinum. These digital temperature sensor PCBs are widely known for their precision and accuracy.
RTDs can control heat within a range of -200°C to 850°C. Although it can vary by sector. The typical deployments are HVAC, lab equipment, power plants, and industrial process control. Besides, it is ideal for measurements where stability and repeatability are essential.
Thermistors (NTC/PTC)
Thermistor sensors are temperature-sensitive. The sensor operates by changing its electrical resistance, which allows it to measure temperature variations. Where should you use this? For affordability and small PCBs, it is an ideal choice. Also, you may utilize it to measure accurate temperature readings. Additionally, it contains a thermal response of up to -100Ω/°C at 25°C.
It generally comes in two varieties. One is NTC and the other is PTC. With NTC (Negative Temperature Coefficient), you can work within a range of -55°C to +200 °C. Some specialized NTCs can perform at nearly zero temperature, like -273.15°C.
On the other hand, PTCs are used to protect against the overflow of currents. Typically, the temperature range from 60°C to 120°C is better for operation.
Temperature Sensor PCB Design Considerations
Designing a PCB temperature sensor needs careful planning. A small mistake in layout or grounding can lead to inaccurate reading. That’s why you must work with a skilled PCB designer or a trusted PCB manufacturer. They typically know how to handle power noise, reduce interference, and place components at the correct location.
Poor design may affect sensor responses. It could also damage components or even cause failure in real-world use. In this case, high-quality design typically ensures stable performance and long-term reliability. Whether you need it for industrial machines or consumer electronics, professional PCB design makes a big difference.
PCB Layout Design Considerations
For PCB Layout design, there are a few crucial measures to take into account. If these instructions are not followed during the process, some issues may arise. So, to avoid them, make sure you have gone through these design considerations.
Power Supply and Grounding
IC temperature sensors use analog circuits that are sensitive to supply noise. Therefore, place a capacitor of 0.1 μF to 1 μF close to the VSS or VDD supply pins. This helps to protect from power supply blunders and will slow the transient noise. If you want to increase the effectiveness of the capacitor, you may add a resistor in series. It will form an RC filter for noise reduction.
This way, proper grounding and a short return path improve accuracy and stability.
Signal Integrity and Noise Reduction
An analog sensor may make noise from external sources or traces. To avoid this, you may need to add an extra capacitor on the output. This way, you can minimize the overshoot or undershoot.
Some microchips can drive large capacitive loads, which makes them suitable for long PCB traces. For RTDs and thermocouples, add EMI filters in the first stage at the input point.
If you want to improve small signal amplifications, use low-offset and high CMRR amplifiers. Examples are auto-zero or chopper amplifiers.
Thermal Considerations
Placement of the sensor also affects heat or temperature accuracy. Therefore, you should not place sensors near the regulator, amplifier, or other heat sources. Use a cold junction for thermocouples. It will help you to sense the reference temperature easily.
Avoid using copper layers under the sensors, as you know, copper is highly conductive. It may transfer heat and can cause errors. Sometimes, these issues can hamper the performance of the board as well. For this reason, thermal isolation is essential to maintain stability in a sensitive design.
Component Placement and Routing
Good placements cut down the chance of errors and noise pickups. So, make sure the decoupling capacitors are placed next to the sensor supply pins. For analog output sensors, keep all the signal traces away from the signal line. It will help you avoid interference.
For RTDs or thermocouples, use symmetric RC filters at different inputs to maintain noise rejection. For accuracy, RTD precision reference resistors should employ Kelvin connections. Place Amplifiers and PGAs near the sensor to minimize trace length.
Testing and Calibration of Temperature Sensors on PCB
For precision, it’s essential to test and calibrate temperature sensors on the PCB. Starting with functional testing, it checks whether the sensor is giving proper signals. Usually, this testing is conducted in normal conditions.
Environmental testing is also an essential part of it. It exposes the board’s suitability and stability in various temperatures. During calibration, readings from sensors are compared to a standard temperature. In this case, you can adjust things to minimize the fault. You may also test it for repeatability and response timing. In particular cases, there are tests for humidity and vibration. Overall, proper testing can help you achieve the best outcome from PCBs.
Summary
Let’s summarize the discussion. The temperature sensor PCB design needs your careful attention. As you know, some temperature sensors are made for regular temperatures, while others are for extreme situations. You must choose the right one for your project.
When you add these sensors to a PCB, you must also pay attention to meeting design criteria. The wrong layout can give inaccurate readings or may not give you a durable solution.
Poor product performance also affects customer satisfaction. You may not get returning customers, which will affect your business’s trust. Therefore, it is always wise to choose an expert PCB maker. They know how to reduce noise and keep signals clean. You should also test the sensors after making the PCB to ensure they function correctly.
If you are interested in a temperature sensor PCB, UETPCB is available to assist you with the project. For more information, feel free to contact our customer support team.