How to Choose a Temperature Sensor for IoT

February 26 2016
temperature sensor

Choosing a temperature sensor for connected hardware applications may seem like a straightforward decision. Everyone has experience monitoring the temperature using their own sense of hot & cold, analog thermometers, and the many digital temperature displays on thermostats, car dashboards, and smart phones. But selecting the right temperature sensor for Internet of Things applications involves taking many factors into account and is not a simple decision.

For example, our customers here at Temboo build and run IoT applications for aviation, agriculture, manufacturing, research labs, and many other industries. They’re measuring the temperature of very different things in very different settings with very different needs. Choosing the right temperature sensor in each case requires taking into account the scale, location, budget, and intended use of your IoT application.

“I generally dive into looking for sensors with Octopart; then I look at Digikey, Texas Instruments, and Mouser; and other suppliers to find out what exists and compare them. You really want to make sure you’ve got all the information you need.” – Claire Mitchell, Temboo Product Team

Deciding on an IoT Temperature Sensor

With Temboo, the choices for hardware are near limitless. Our software libraries come pre-installed on hardware platforms from Samsung, Texas Instruments, and Arduino, and our downloadable SDKs work on many devices. And since most sensors only require a few GPIO pins to connect a hardware board, the available choices are almost endless.

Today, we’ll cover temperature sensors in general and the rationale for our choice of temperature sensor used in our Connected Sensors IoT Application. In general, it’s important to keep in mind a few key factors when picking sensors:

  • Cost: How much will it cost? Are the costs scalable if I use this component? This is important to consider so that the solution remains truly cost effective.
  • Supplier: Where can I get it? How trustworthy is this seller? Make sure the supplier has reviews from other buyers that indicate on-time shipments and quality merchandise.
  • Accuracy & Precision: How reliable are the measurements? How accurate and precise do you need your measurements to be? Monitoring biological stock on an industrial farm will require more accurate temperature sensors than monitoring the conditions in a living room.
  • Accessibility: Can I get it for my planned project? What is the scale of the project? Certain components can only be bought or ordered only when the demanded size is in the millions, it’s important to know if the minimum batch size is compatible with your industrial needs.
  • Measurement Range: What ranges will it work for? It would be foolhardy to get a temperature sensor that only works above 40°C to monitor freezers – make sure that the range is applicable to what you want to use it for.
  • Power Consumption: Will it work with the power source I have? Make sure the power the sensor consumes is compatible with the system; it would be disastrous if the circuit has too much current and blows out the sensors.

IoT Temperature Sensors We Looked At

Texas Instruments LMT84LP

Texas Instruments’ LMT84LP, the sensor that we chose for our cloud-connected sensors. It’s got great precision at a very competitive price with industrial-grade quantities:

  • Cost: Scaling down from $0.91
  • Supplier: Mouser Electronics
  • Accessibility: Available in various industrial quantities, but also smaller batches
  • Accuracy & Precision: +/- 0.4°C
  • Measurement Range: -50°C – 150°C
  • Min~Max Voltage: 1.5V – 5.5V
Texas Instruments LM35DZ

Texas Instruments’ LM35DZ, although used commonly amongst the DIY community, it is not something that would be able to fulfill our needs for a sensor suitable in industrial usage due to its precision range and costs per unit:

  • Cost: Scaling down from $1.86
  • Supplier: DigiKey
  • Accessibility: Available in various industrial quantities, but also smaller batches
  • Accuracy & Precision: +/- 1.5°C
  • Measurement Range: 0°C – 100°C
  • Power consumption: 4V – 30V
Sparkfun DS18B20

Sparkfun’s DS18B20, wired probe sensor. With a heftier price tag, it wasn’t suitable for our intended usage on industrial farms but might be interesting for those working in more extreme environments:

  • Cost: Scaling down form $9.95
  • Supplier: SparkFun
  • Accessibility: Available in various industrial quantities, but also smaller batches
  • Accuracy & Precision: +/- 0.5°C
  • Measurement Range: -55°C – 125°C
  • Power Consumption: 3.0 – 5.5V

 

Atmel AT30TSE754A-SS8M-T

Atmel’s AT30TSE754A-SS8M-T, with a price point much more enticing than our pick for the cloud-connected sensors, we passed over this choice only because of the less precise nature of the instrument:

  • Cost: Scaling down from $0.53
  • Supplier: DigiKey
  • Accessibility: Only available in quantities at or above 4,000
  • Accuracy & Precision: +/- 1 – 3°C
  • Measurement Range: -55°C – 125°C
  • Power consumption: 1.7V – 5.5V

For our Connected Sensors IoT App, the intended use case is monitoring the temperature of delicate assets such as biological stock that can go from good to bad in the span of 0.5°C. To enable a mass-produced and production-ready sensor solution, our main considerations were cost and accuracy. The Texas Instruments’ LMT84LP thus fit our needs because of its relatively high accuracy and low per unit cost. Had we been monitoring machines, we could potentially have gone with a less accurate temperature sensor, as the difference between a degree point or two for an industrial machine would still result in the same automated system shutdown or cooling procedure.

“You’ll not only want to find the sensor that meets your application’s requirements for range and accuracy, but is also easily accessible in the right quantities for your devices.” – Kevin Buck, Temboo Engineering

However, priorities may shift for developers who are looking for temperature sensors that work under special conditions (such as the DS18B20 for underwater projects) or require sensors that work under different power consumption levels. For cases where the deployment is on a larger scale or requires a higher-touch of customization, it may be best to approach a sensor manufacturer directly to request sensors that would fit the solution’s needs. There are many sensor manufacturers out there–this exhibitor list from the upcoming Sensors Expo & Conference  is a good resource to start investigating them.

Why Choosing a Temperature Sensor Matters

40% of the food produced in the United States is wasted, in many cases not even making it to your table through the distribution chain. Recently vaccines worth $1.3M spoiled in Pakistan, imperiling the health of many. Aviation firms spend millions of dollar each year complying with audit requirements to ensure their equipment is safe. These are just a few industry examples where better temperature monitoring will significantly reduce costs while also bringing big benefits to health, safety, and the environment. The Internet of Things enables companies to improve their bottom lines while making the world a better place.

Our Connected Sensors IoT App can serve as an off-the-shelf temperature sensing solution for your business, and since Temboo automatically generates the application code for the device you’re using, you can modify and extend the IoT application so that it becomes a custom solution for your own business’s needs. Start building your own temperature sensing IoT application today.

Choosing a temperature sensor for connected hardware applications may seem like a straightforward decision. Everyone has experience monitoring the temperature using their own sense of hot & cold, analog thermometers, and the many digital temperature displays on thermostats, car dashboards, and smart phones. But selecting the right temperature sensor for Internet of Things applications involves […]