Industrial control engineers need to use Zigbee technology? You do not need to become an RF expert!

Industrial control engineers need to use ZigBee technology? You do not need to become an RF expert!

Both Zigbee and IEEE 802.15.4 are low-speed wireless network standards, which can save expensive and easily damaged connections in industrial control products. In this way, liquid or process control equipment can be placed at will and can still communicate with other systems. Because the network has no requirements on the location of sensors, pumps or valves, the device can also be moved.

The ZigBee standard is developed based on the IEEE 802.15.4 standard. All ZigBee products are also 802.15.4 products. The standard ZigBee part is designed to ensure that devices of different manufacturers can still communicate with each other and support a complex, self-healing "mesh" network with up to 65,000 nodes. The ZigBee standard is still developing, and the Framework Structure of some applications is not yet defined.

However, ZigBee wireless networks are not required. Many easily implemented 802.15.4 applications already have sufficient functions. In point-to-point or star network, products do not need to interact with devices of other vendors. 802.15.4 is the best solution. If a higher ZigBee application layer is not defined, 802.15.4 is the only choice. Once an appropriate application framework is promulgated, these applications will be integrated into the ZigBee Specification.

Whether the network is 802.15.4 or ZigBee, it still has various nodes: control nodes, full functional nodes, and simplified functional nodes. Each node must have at least one RF Device, microcontroller, and media access control software that manages RF and system interfaces.

In most wireless network applications, networks are applications. For industrial control products supporting 802.15.4 or ZigBee, the main application is industrial control systems, and wireless networks are used to control inter-system communication. In this way, when the ZigBee function is added to the industrial control system, two separate systems can be designed in parallel. This hinders the implementation of wireless networks because most industrial control engineers do not want to become RF experts.

Fortunately, 802.15.4/ZigBee RF and controller vendors are aware of this fact and are ready to provide a highly integrated system-level solution. Therefore, engineers do not need to become RF experts. However, they need to understand RF parameters and their impact on system complexity, cost, and power consumption.

Receiver sensitivity and power output. When evaluating ZigBee/802.15.4 RF, the main parameters are receiver sensitivity, transmission power, and link costs.

The receiver sensitivity refers to the minimum power for the radio to reliably receive data. The unit is dB (dBm ). A larger dBm value indicates a higher receiver sensitivity. The larger the negative dB value of the receiver sensitivity, the larger the RF interval and the less RF required, which will undoubtedly help reduce costs. 802.15.4 standard stipulates that the minimum receiver sensitivity for 900 GHz RF is-85 dBm, And the MHz is-92 dBm. All vendors of 802.15.4 have exceeded this standard, and the receiver sensitivity is between-90 dBm and-100 dBm. Although 10 dBm does not seem to be much different, it has a significant impact on the scope of impact and system costs.

If the RF receiver sensitivity is increased from-94 dBm to-100 dBm, the RF operation distance is doubled. For example, if the RF distance of the receiver sensitivity is-94dBm is 100 meters, the range can be extended to 100 meters if the sensitivity is increased by only 6 dBm, I .e.-200 dBm. More importantly, increasing sensitivity can avoid the use of expensive high-power amplifiers (PA), thus reducing the complexity, cost and power consumption of the system. Based on these factors, engineers can choose high-sensitivity RF.

The second important factor for extending the RF distance is the sending power. The larger the RF transmit power, the larger the signal range. The minimum output power required by the 802.15.4 standard is-3dBm, that is, 0.5 mWatts. The current market RF output power is between 0 dBm (1 mWatt) and 3 dBm (2 mWatts. The larger the output power, the better the performance. In fact, the larger the transmit power, the less demand for external components such as the power amplifier, which is conducive to reducing costs. In addition, the power required by the amplifier is also great, will affect the battery life of the terminal node.

The receiver sensitivity and transmission power both affect the transmitter/receiver range. The higher the receiver sensitivity, the larger the sending power, and the longer the working distance. Even in buildings, high transmission power and good receiver sensitivity can improve the reliability of the RF link.

The absolute value of the receiver's sensitivity and output power is also known as the "link budget", which is related to the working effective distance.

Assume that the network requires 1000 low-cost budget nodes, and only 357-103dBm Atmel radio frequencies are required to achieve the same coverage. The cost for each node is 10 US dollars, so that the cost of a system that costs 10,000 US dollars is only 3,570 US dollars.

If you need to add ZigBee or 802.15.4 wireless features to your product, industrial control engineers do not need to become RF experts. But they must understand the impact of receiver sensitivity, transmission power, and link costs. In either case, you must overwrite the given region with the lowest dBm value, a longer effective range, and fewer nodes.

In addition to link costs, the number of external components also affects system costs and application board space. The external components are generally passive filters and crystals used to generate the clock signals required by the system. The number of external components must be published in the seller's documentation. In this way, the fewer external components, the better, regardless of the cost or product placeholder pin.

Author profile: Chris Baumann is the director of the Atmel BiCMOS product business department. He joined Atmel in 1989 and previously worked for TI and Honeywell. Mr. Baumann has a bachelor's degree and a Master's degree in electronic engineering from the University of Notre Dame.