Sensors and relays: the eyes, ears and hands of a building automation system

By Fabrizio Petris, senior business development manager, Omron Electronic Components Europe 

The Omron HVC module is the first vision module specifically aimed at applications like building automation

Until now, energy efficiency measures have focused on the construction of the building, looking at for example the insulation and windows. The new Energy Performing Buildings Directive, adopted in 2018 and mandatory from 2020, marks a significant shift, increasing the focus on the control of energy use within buildings: smart buildings and building automation. This should be music to the ears of building managers everywhere. Smart buildings offer an excellent RoI, but it is still difficult to get the initial capital required signed off. The new directive will help, giving the planet reduced carbon emissions and owners reduced costs. In addition, smart building systems can be extended to additional functions such as security and improving the comfort of occupants. New technologies are continually emerging to enhance smart building systems and reduce their cost. This article surveys the state of the art in these technologies starting with sensors that provide the data and moving on to control components that enable the system to act on it.

Image recognition

Using image recognition technology originally created for mobile phones, building automation systems can interpret the image collected by a camera. They can see and respond to gauge their mood, their age and their gender. They can also recognise an individual. Using these sensors, security systems and building automation systems could eventually be integrated together using one set of vision modules. The data they collect can be responded to automatically, saved or collated centrally, and passed to an operator only when necessary.

Potentially, an office can recognise an individual when he or she arrives, and set up heating and lighting just the way they like it.

Wide angle thermal sensors like the Omron D6T 32 x 32 can encompass a whole room in their field of view, detecting potential fires as well as the presence of people

The Omron HVC module (Figure 1) is the first vision module specifically aimed at applications like building automation, available in low volumes and readily integrated by any designer without any need to understand the complex algorithms needed to recognise faces and expressions or the optical design. The module is a fully integrated, plug-in solution. The developer can just look at the outputs and configure the system to make appropriate decisions depending on their status.


Thermal sensors

Where the application calls simply for the detection of people without the need for recognition, thermal sensors are a well-established option – and a great alternative to motion sensors. In a building automation system, such sensors can also be used in many other ways, making a valuable contribution to safety by identifying potential problems before they become major hazards. Many fires, for example, start with localized ‘hot spots’ and a thermal sensor can detect a potential fire before it ignites. This can not only save lives but also costs, allowing preventative maintenance to be undertaken in a timely manner.

To be useful in a building automation environment, such sensors need a wide field of view, to detect the presence and location of people and other issues in a space accurately and reliably. Omron D6T MEMS thermal sensors are based on an IR sensor which measures the surface temperature of objects without touching them using a thermopile element that absorbs radiated energy from the target object. Omron has just released a wide angle version of the D6T (Figure 2) with 32 x 32 elements. The D6T-32L-01A can view across 90.0° by 90.0°, encompassing a wide area such as a whole room from a single point.

Environmental sensors

Human operators of systems monitor their environment the whole time, often in ways that we’re not aware of. We respond to the breeze on our face, movements in our peripheral vision, small changes of pressure in our ears and in the soles of our feet. A smart building needs to do the same, responding to changes in its environment to optimise energy efficiency and occupant comfort.

The Omron 2JCIE measures seven popular environmental parameters in one compact unit

Multi-purpose environmental sensors make it very easy for the designer to deliver a wide range of measurement functions from just one small sensor. This will save development time by providing numerous options that can be tailored to the user’s needs. Whether it’s a question of simply making sure the office environment is kept at the optimum working temperature or ensuring that say a museum has the correct humidity and lighting to protect the exhibits, these sensors offer easy to interpret data that can then be analysed and used to set parameters and make real-time adjustment.

There are probably seven core parameters that any environmental sensor for building and industrial automation systems should be able to monitor: temperature, humidity, quality of air VOC, light, barometric pressure, noise and acceleration. Sensors like the Omron 2JCIE (Figure 3) provides the capability to monitor all of these, and provides data via popular wireless and wired data interfaces like USB and Bluetooth. Despite its compact size, 2JCIE features its own ded memory for data logging to keep track of the surroundings.

Air quality

Ventilation and adequate air quality in a building is a major issue, and building regulations in countries including the UK make detailed stipulations about adequate mechanical ventilation rates in spaces including non-habitable rooms, such as toilets, bathrooms/shower rooms, kitchens and utility rooms in domestic dwellings.

Whilst building engineers will ensure that such spaces are designed with fans and other means of ventilation that comply with the regulations, building managers need to maintain those fans and ensure that their performance has not dropped below the required level due to wear or to a buildup of dirt in the airway. Suitable sensors are available to help with this task. Omron’s D6F-PH digital pressure sensors (Figure 4) for air flow and clogged filter detection in heat recovery units do this by detecting the differential pressure upstream and downstream of the fan or filter, detecting the degradation in performance as it becomes clogged with dirt and providing an alert when cleaning or replacement is required. A more compact alternative is the 2SMPB barometric pressure sensor. The Omron D-6FV can improve efficiency by monitoring the exact air rate at which air is extracted by the fans.

Controlling the outputs

If these sensors are the ‘eyes and ears’ of a building automation system, it also needs ‘hands’ to act in response. It needs control over outputs: heaters, lights, fans and other elements. Relays are still a great solution. Open the case of almost all building automation systems and you’ll find electromechanical PCB relays used at the output. With so many alternative switching technologies available, including solid state switches, this may come as a surprise. There are four important reasons behind this.

  • Relays have one or more relay contact outputs
  • Contacts can be supplied with a changeover output which is used for interlock or scanning circuits
  • Relays can individually switch AC or DC voltages
  • Relays simultaneously meet insulation and glow wire test requirements

Because loads vary enormously and the latest technologies place new demands on relays, manufacturers like Omron have developed platform relay series that address all of the different requirements. For example, its G5Q family offers different specifications with the same PCB connection to meet different switching needs.

In common with other classes of components, relay manufacturers are being challenged to make their components more compact. Designs that are almost 30 mm long used to be perfectly acceptable – not any more. The G5Q, for example, is a high specification industrial relay but is only 20mm long by 15 mm high by 10.3mm deep.

Specific applications have their own challenges. For example, LED lighting, water pumps and capacitive input filters with Power Factor Correction produce high inrush currents. This puts extreme loads on relay contacts. If relay contacts weld together this destroys the relay and thus the device. Type G5Q-1A-EL2 (Figure 5) was developed for capacitive inrush currents in the µs range. Such relays can switch inrush currents of 40 A/100 µs and nominal cut-off currents of 1 A/250 V AC up to 100,000 times.

The same design is available for inductive motor loads (e.g. fans) which have inrush currents in the ms range. The G5Q-1A-EL3 is designed accordingly and can perform approximately 300,000 operations with 250 V AC/30 A 500 ms inrush currents (inductive load) with a 3A cut-off current.

The G5Q-1A-EL can handle such switching tasks and offers a long service life (100,000 operations) for general standard applications (resistive load) with high contact loads (10 A/250 V AC) where relays are often subjected to high temperature rises.

To save power latching, designs are also available, such as Omron’s G5RL-U (Figure 6), G5RL-K and the G5RL-HR that can switch up to 16A and are capable of dealing with high inrush currents of up to 150A.


As awareness of the impact of wasted energy in buildings is increased, the technologies on offer to conserve this energy and control its use has improved dramatically. The sensors and relays described above put building managers in an excellent position to reduce both costs and carbon footprint. With the development of the cloud, they no longer even need to be present in a building to receive a full picture of what is going on. All of the data collected and the actions taken by the system in response can be stored on the cloud, and reviewed by the building manager. He or she can reprogram the system to improve its response in the light of experience, or even intervene directly if needed. Truly, ‘dumb’ buildings are becoming a thing of the past.

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