Blog August 5, 2020

Why Thermocouples aren’t Good Choices for Wireless Concrete Sensors

Thermocouples have been around for a very long time and have been used in almost every industry in some capacity to measure temperature values at specific points or of certain materials. We’ve broken down the workings of thermocouples, their various types and metal combinations, as well as the Thermoelectric Effect in much more detail in a previous blog post, but the fundamental concept is quite straightforward. The Thermoelectric Effect states that if two metals are joined together at one end and experience a temperature delta (difference in temperature at either end of the metals) then a voltage will be induced. This voltage drop across both ends of the joined metals is then amplified and translated – using either a manual calibration chart or a pre-calibrated digital reader, depending on the price and caliber of the device – into a temperature reading. 

When we talk about wireless concrete sensors – specifically wireless concrete temperature sensors – we refer to digital devices that can measure and transmit data without the need for complicated wiring or prolonged human interaction. These sensors have a lot of technology packed into their enclosures – a result of the rapid advancements over the past few years, including wireless connectivity and intelligent battery management – that allow them to be portable, reliable, and accurate throughout the duration of any project. One of the key details that hasn’t been mentioned in any of our previous blogs, however, is that not all wireless concrete temperature sensors use the same technology to measure temperature data. 

Thermocouples in Wireless Concrete Sensors

Most wireless concrete temperature sensors on the market come in the form of individual devices with some type of probe attached to them. They can be embedded within a concrete slab prior to pouring, with each device measuring and transmitting data using some type of low-range communication protocol like Bluetooth. The reason that these devices come as individual packages are because they use the same thermocouple technology to measure temperature. As stated before, a thermocouple is just two metal wires joined together, one end placed in the specific material or medium that is to be measured (the hot side) and the other end exposed to ambient temperature (the cold side). The probe on the wireless concrete temperature sensor is the hot side of the thermocouple. The voltage drop across the probe is then automatically converted to a temperature reading and transmitted to the user once they’re in range. 

Thermocouple-based wireless concrete sensors may be common in the market, but they have some major drawbacks. The first is their accuracy. An unavoidable problem with thermocouples is that – because their temperature reading is based on a voltage drop – their accuracy is dependent on not just the combination of metals used but also on how the device is calibrated by the manufacturer or supplier. This can cause a lot of variation in temperature readings for different wireless concrete sensors. Certain metals have higher temperature tolerances and heat capacities than others, which could become problematic if they’re used in a variety of applications at a single job site. Thermocouples are not resistant to Electromagnetic Interference (EMI), so if there are any machines, power lines, or other power-driven tools operating nearby, their presence alone could affect the behaviour of the thermocouple probes and, in turn, the temperature reading.

Another issue with thermocouple-based wireless sensors is scalability. A single wireless sensor can only measure the temperature of a very small area and isn’t capable of measuring the internal temperature of a large slab of concrete on its own. To get a complete look at the curing performance of each concrete slab, multiple devices would need to be installed in a grid within the slab, incurring more time for manual installation. Plus, since these devices are considered “sacrificial” – they’re installed within a concrete slab and left there even after the slab is cured – construction companies would need to order hundreds of sensors for something like a multi-storey residential building. Bluetooth – although very power efficient – has a limited transmission range. When embedded within a slab of concrete, that range reduces dramatically. This means that for large-scale projects – which require the use of multiple sensors per slab – someone needs to be on-site and within range of each sensor in order to collect data, which poses issues during times when staff is limited due to health concerns or regulations. 

Digital Wireless Temperature Sensors

Digital wireless temperature sensors don’t share the same limitations as thermocouple-based sensors, allowing them to be versatile and adaptable to a number of different project requirements. These sensors are much more accurate and – because they’re just a series of integrated circuits – can be daisy-chained together as a single cluster to easily measure temperature at multiple points across long distances. Adding to that the integration of advanced communication protocols like 802.11 Wi-Fi and LoRa, these devices are able to send temperature readings directly to the cloud, allowing project managers to remotely monitor and track the curing stages of their concrete slabs without ever stepping foot at the job site.

Digital sensors can be housed within protective sheaths, conduits, or enclosures, giving them full EMI resistance. Since they don’t require a physical probe, digital sensors are also quite a lot smaller than thermocouple-based sensors, and can be fit into areas that were previously inaccessible by other sensor types. Intelligent battery management software allows the circuitry within the sensors to be very power efficient. When paired with their water-tight and rugged outer enclosures, digital wireless temperature sensors can remain fully operational and reliable throughout any project duration.

Although they are still “wireless sensors”, the implementation of thermocouples in some wireless concrete sensors carries over some of the limitations and drawbacks of traditional thermocouple technology. Digital sensors harness the power of new technologies like IoT and integrated circuits to make these small devices much more capable, accurate, and reliable in any type of construction project. 

Interested to learn more about how Wireless Concrete Sensors can help in your next project? Schedule a call today and find out!