Blog March 6, 2020

Thermocouples vs. Wireless Concrete Sensors

Out with the old. In with the new.

Construction is one of the slowest industries when it comes to technology adoption. As the global consumer market – and in fact most other industrial markets – surge towards a new data-centric era, construction continues to lag behind, sticking to more traditional methods throughout project execution. One of those methods is the use of thermocouples for measuring concrete temperature. 

Concrete is a vital material in any construction project. Each slab cures slightly differently than the next, so keeping a close eye on their internal temperatures is important to maintain the project schedule. But for projects that have hundreds of slabs, the idea of individually recording temperatures using a handful of thermocouples is extremely tedious.

Today, however, there’s another solution readily available to solve this problem, and they come in the form of wireless concrete sensors.

In this blog, we’ll take a deeper look at how thermocouples work as well as their major limitations in the construction site. We’ll then focus on how new technologies like wireless concrete sensors alleviate these pain points while providing unique and highly beneficial opportunities to get the most out of your concrete.

Thermocouples

How do they work?

Unlike traditional mercury thermometers – which rely on the physical state of liquified metal to determine temperature – thermocouples use the thermoelectric effect to measure temperatures with a higher degree of accuracy. 

But what is the thermoelectric effect? 

Thomas Seebeck, a 19th Century German physicist, discovered that if two ends of a single piece of metal were at different temperatures, an electric current would flow through it. He also found that by joining two different types of metals at opposite ends (junctions) and creating a temperature differential between them (making one junction hot and the other junction cold), the measurable voltage across the two junctions would be proportional to the difference in temperature. This effect, however, is heavily dependent on the types of metals being used, since all metallic elements on the periodic table have varying levels of thermoelectric conductivity. 

So in effect, a thermocouple is just two metal wires joined together at both ends, with one end used as a reference (the cold junction) and the other end placed in whatever liquid, material or surface that’s being measured (the hot junction). The wires are wrapped with a protective sheath to prevent the outside ambient temperature from affecting the readings. Since the voltage drop across the two metals is so minute, an amplifier is also connected to the circuit to boost the voltage to values that are easy to interpret. Thermocouple manufacturers usually provide a pre-calibrated chart – like the one pictured below – showing specific voltage values and their corresponding temperature readings.

Thermocouple Calibration Chart

Thermocouple manufacturers always provide a calibration chart that shows a grid of voltage readings and their corresponding temperature estimates on the X and Y axes. After obtaining the voltage from the thermocouple, you can then use this chart to get an idea of the internal temperature of your concrete slab.

Thermocouples are widely used in almost every industry and come in all sorts of types for specific temperature ranges. As mentioned before, the thermal performance of the device depends on the combination of metals used for the wires. Elements like platinum and rhodium are expensive yet better suited for extremely high temperatures (up to 3100F, or 1700C), whereas nickel and copper are a lot cheaper but work best in the cold (down to -454F, or -270C). 

Thermocouples in the Construction Site

The most common type of thermocouple used in the construction industry is Type K. Made from a combination of nickel-chromium and nickel-alumel alloys, these devices are inexpensive, fairly easy to use, and can operate within a wide temperature range at a relatively high accuracy. At first glance, they should be the perfect temperature measurement solution, but the problems start when you actually try to gather data from them.

Remember that thermocouples function off of the thermoelectric effect. The number that they output is actually the voltage drop across the two wires rather than a proper temperature reading. Once you know the voltage, you can match that with a calibration chart (seen above) and get a ballpark estimate of the temperature. Now imagine performing this multi-step process for over 100 points within a single concrete slab. It would be far too time-consuming and could severely delay the entire project schedule. 

There are external devices on the market that come pre-calibrated to show temperature readings automatically based on the voltage, but they’re usually quite expensive, add unnecessary wiring to your already busy setup, and – because most of them are made from third-party manufacturers – sometimes not as accurate. 

Taking all of this into account, it’s clear that thermocouples are not the best temperature sensing solution for construction sites. Although they read temperatures far more accurately than normal thermometers, they’re impractical for large-scale projects. But with the recent advancements in technology as well as the ever-increasing demand for construction, there is a new solution on the market that picks up where the thermocouple left off.

Wireless Concrete Sensors

Wireless concrete sensors are a huge leap forward in construction technology. They come as a combination of hardware and software to bring you valuable insights pertaining to your concrete slabs at the touch of a finger. Let’s break them down.

Hardware

An important part of what makes wireless concrete sensors such a game-changer is their advanced hardware. Concrete sensors come in all shapes and sizes, but their underlying purpose is to be physically embedded within a concrete slab prior to pouring, collect vast amounts of concrete temperature data, and send that information to you over the air. Their enclosures are usually waterproof and resistant to chemicals or vibrations in order to protect the electronic circuitry on the inside. The embedded sensing, processing, and communications circuits are also very power efficient, meaning these devices can stay online and collect data for months at a time. 

To transfer concrete temperature data to the user while preserving battery life, manufacturers integrate Bluetooth connectivity into the system. Since Bluetooth operates at 2.45GHz, data is able to effectively punch through the concrete slab without any significant loss provided that you’re within range of the sensors.

However, some concrete sensors come with sophisticated networking architectures built-in. Instead of relying on localized low-range networks, these sensors transmit concrete temperature data directly to the cloud. That means you don’t actually need to step foot on the construction site in order to know the temperatures of your concrete slabs. As long as you have an internet connection, you’re able to remotely monitor their curing progress from anywhere and on any device. 

But in today’s data-centric age, collecting concrete temperature data isn’t enough. It’s how you use it to optimize your processes is what’s important, and that’s where software comes into play.

Software

Advanced and sophisticated analytics software turns your concrete temperature data into more than just a set of numbers. Predictive algorithms can use the information gathered by concrete sensors to establish an accurate timeline of exactly when your slabs will be cured and when you should send a sample to the lab for strength testing. This feature alone saves a huge amount of time and money, since you no longer need to work off of general estimates (ie. the “70-in-7” rule). 

What makes this particularly exciting is that AI is a dynamic technology. It’s able to learn and adapt to specific situations based on previous information. We’ve covered how AI-powered software can bring great benefits in project schedule optimization in a previous blog. The idea is that as data – such as internal concrete temperature – is collected from multiple projects over time, it helps the software generate a more streamlined, cost-effective, and optimized project schedule. 

Looking Towards The Future

It’s no question that the global need for construction projects is at an all-time high. It’s also no question that it will continue to exponentially increase as the years go on. But in order to keep up with the seemingly infinite demand, the construction industry as a whole needs to focus on eliminating project delays and making their processes as lean as possible. Wireless concrete sensors brings the industry one step closer to reaching that goal.

Want to learn more about how concrete sensors can help in your next project? Schedule a call today to find out!