Creating building automation-ready smart meters, fire alarms and security cameras Analysts predict that the market for building automation systems will double in the 5 year period up to 2023 analysts predict the global market for building automation systems will double in size as building designers seek to improve the safety, reliability, convenience, comfort, and energy efficiency of domestic and commercial buildings. This has significant implications for the design of systems that have been present in buildings for some time which now need to be connected and smart. Examples include energy meters, fire and smoke alarms and security cameras. How can designers of these products bring their solutions up to date?
David Pearson, Technical Director at Anglia looks at how some solutions from Littelfuse can help developers achieve class leading performance whilst meeting design challenges and budget constraints. Littelfuse has a long history of developing high performance and reliable solutions for the Smart Building sector, they continue to innovate with a broad and diverse offering of protection devices, for which they are best known, along with products for control and sensing applications.
Modern smart meters are extremely sophisticated pieces of equipment at the forefront of the campaign to address climate change by reducing wasted energy. Traditional meters which just measure the amount of energy used are being superseded by units which can share meter readings and usage data with power utility companies via the IoT using a wireless communication interface such as the mobile phone network. The design of these smart meters incorporates several elements besides the actual metrology unit such as a wireless interface, anti-tampering components, and an auxiliary load output for extensions into individual units within a building.
Figure 1. Typical Smart Meter Block Diagram
Littelfuse has a wide range of components which can be used across the core blocks of a typical smart meter design shown in Figure 1. In the metering unit (1) they can offer Metal Oxide Varistors (MOV) and TVS Diodes to protect the power unit from lightning and voltage transients. An example is the popular UltraMOV series of radial leaded varistors which are designed for applications requiring high peak surge current ratings and high energy absorption capability and offer the design robust protection. In addition, Littelfuse has a range of Thermally Protected Varistors, TMOV series, which take protection to the next level by integrating a thermally activated element with the MOV which is designed to open in the event of overheating due to the abnormal overvoltage, limited current, conditions outlined in the UL 1449 standard.
For overcurrent protection Littelfuse has a comprehensive range of cartridge fuses and Resettable PPTC fuses suitable for this circuit block along with NTC thermistors which can be used to limit high inrush currents and Si and SiC MOSFET for high frequency load switching.
For the wireless communication interface (2) TVS Diode Arrays are a good option to protect against any user induced ESD events along with a SIDACtor® device such as the Littelfuse SEP series which features low insertion loss, low clamping voltage and log-linear capacitance and can protect against lightening surges. Whilst solid-state relays (SSR) can provide the isolation required between the MCU and wireless interface.
On the important Anti-tamper (3) part of the design, Reed Switches can be employed to prevent any magnetically induced tampering with the unit, and finally in the Auxiliary load output (4) again MOVs and TVS Diodes can be specified to protect I/O from voltage transients caused by overloading and SSR’s to provide isolation to the MCU.
Gas and water meters differ to electricity meter designs because they will typically be battery powered instead of mains powered, however they still share many of the same functional circuit blocks making the Littelfuse product range applicable for these designs as well.
Fire and Smoke Alarms
Similarly modern fire and smoke alarms do much more than trigger a loud bell when an issue is detected. Connected and smart alarms send a message when they detect heat or smoke either directly to the fire service or to an external building management services team via the mobile phone network.
Inside the alarm, signal lines link the MCU and digital signal processing to the wireless interface, temperature and gas detectors, test push button, and USB port (used for programming). Designs that receive power from AC mains rather than from batteries also have to convert the power to DC at the correct voltage level. Both the signal and power elements of this design require protection from overcurrent and transient voltage events, again Littelfuse has a wide portfolio of suitably high performance and reliable solutions.
Figure 2 - Typical Fire and Smoke Alarm Block Diagram
Within the AC/DC power stage (1) we will find overcurrent protection fuses, MOVs to protect against voltage transients and lightning strikes. MOSFETs such as the Littelfuse X2-Class series can be used within the SMPS switching circuit, these MOSFETs exhibit low on-state resistance, along with low gate charge and superior dv/dt performance whilst their avalanche capability also enhances device ruggedness.
TVS diodes can be used to protect the sensitive semiconductors in the DC-DC converter (2) block and Resettable PPTC fuses and bi-directional Multilayer Varistors (MLV) can be specified to protect the USB interface (3). For the Temperature Detection (4) block, Littelfuse offer sensors such as the cost-effective KC series of NTC Thermistors which feature high reliability, small form factor and fast thermal response times.
The same thinking applies to the third element of a smart building that we are considering here: security cameras. At its heart, a security camera is an image sensor integrated with a processor and memory. These days, the camera does much more than connect to a console staffed by a local guard. It communicates with a central computer through Ethernet, Wi-Fi, or a radio band to a wireless receiver, sending video images and receiving commands. Often, the system will also include motors for driving a zoom lens and the camera pan/tilt positioning. An AC/DC power adapter and/or onboard battery pack will be used to power the system.
Figure 3 - Typical Security Camera Block Diagram
The power adapter (1) block shown in figure 3 will require overcurrent protection fuses along with MOV and TVS Diodes for lightning and transient protection. For the DC Input stage (2a) and RJ-45 Ethernet interface (2b) there will be a requirement for overcurrent fuses and resettable PPTC fuses to protect the power stages along with TVS diodes and arrays to protect data lines. The Memory Card (3) block on the control board can use TVS diode arrays to protect against ESD events when users insert/remove the memory card. The Motor Drive (4) block needs to be optically isolated from the rest of the control circuit to prevent interference or damage to other components within the system, this can be effectively achieved using a high current SSR such as the CPC1561 series 60V, 1A single pole current limiting relay which incorporates thermal shutdown circuitry for improved survivability in harsh environments.
In this article we have only scratched the surface with a small number of Smart Building application examples, however it is clear that whatever the application requirement for protection, control, or sensing, Littelfuse has a wide range of high-performance products which can meet the design needs.
In addition to the examples shown above Littelfuse has products which are suitable for other Smart Building applications including Smart Locks, Door and Window Sensing, Garage Door, Intelligent Power Outlets, Smart Thermostats, Elevators, Home appliances and many more besides.
Anglia offer comprehensive support for customer designs on the full range of Littelfuse products, with free evaluation kits and samples of products via the EZYsample service which is available to all registered Anglia Live account customers.
In addition, Anglia’s engineering team have extensive experience of working with a wide range of Smart Building applications and can provide valuable product demonstrations, insight, advice, and component recommendations for your application.
To assist designers, the Littelfuse Building and Home Automation Application Guide is also available for downloaded free from https://www.anglia-live.com/supplier/littelfuse. This useful guide details 18 different smart building applications including those above and provides suggestions for product series which can be used within each design along with links to datasheets and application notes.
Anglia are available to support customers with all aspects of their designs, offering hands on hardware and software design support along with access to an extensive resource of technical application notes and support from Littelfuse experts when required.
Visit www.anglia-live.com to see the full range of Littelfuse products available from Anglia.