Application of RS-485 Transceivers in ETC Systems
Advances in technology have enabled highway electronic toll collection (ETC) systems to improve tolling efficiency by allowing vehicles to pass through toll points at higher speeds and in less time. ETC also reduces annual carbon dioxide (CO2) emissions by approximately 42% [1]. As a result, it is gradually replacing conventional manual toll collection and helping ease increasingly severe traffic congestion. Market research indicates that ETC will continue to grow steadily over the next six years, with a projected global compound annual growth rate (CAGR) of approximately 8.9% [2].
TIA/EIA-485-A is the standard for RS-485. It defines the electrical characteristics of a two-wire, half-duplex, balanced-transmission-line, multipoint communication system and was jointly published by the Telecommunications Industry Association (TIA) and the Electronic Industries Alliance (EIA). Digital communication networks that comply with this standard can communicate reliably over long distances in electrically noisy environments. A multipoint bus configuration supports multiple receivers on the same network, making RS-485 well suited for industrial environments.
A highway ETC installation consists of many devices, including IP cameras, RFID antennas, Ethernet switches, remote I/O modules, power meters, and temperature and humidity sensors, as illustrated in Fig. 1. Within the ETC system, a remote I/O module in the system cabinet uses RS-485 to connect to the power meter and the temperature and humidity sensor, transmitting power-consumption data and environmental temperature and humidity information to the traffic control center [3]. Because this equipment is deployed outdoors, it is vulnerable to lightning-induced damage and must also withstand high summer temperatures and low winter temperatures. RS-485 transceivers with surge protection and high reliability therefore play an important role in the system. Amazing Microelectronic Corp. offers RS-485 transceivers designed to meet these requirements, as described below.
Fig. 1. Example of an ETC System
RS-485 Transceivers with System-Level Electrostatic Discharge (ESD) and Surge Protection:
An electrostatic discharge or lightning-induced surge can destabilize electronic equipment or create latent failure risks. Amazing Microelectronic Corp. offers the AZRS8352P and AZRS5354P RS-485 transceivers with system-level ESD and surge protection. Their principal difference is the maximum data rate: the AZRS8352P supports up to 118 kbps, while the AZRS5354P supports up to 8 Mbps. During equipment installation, fault repair, or commissioning, the RS-485 bus may be exposed or touched by technicians. For ESD protection, both devices provide outstanding system-level immunity of IEC 61000-4-2 ±30 kV contact discharge and ±30 kV air discharge, effectively protecting the bus from ESD events. For surge protection, both devices withstand IEC 61000-4-5 ±30 A (8/20 µs), making them suitable for outdoor applications. Their key specifications are shown in Table 1.
| P/N | VCC | Max. Data Rate |
Bus-Fault Voltage |
IEC 61000-4-2 ESD for Bus (Contact/Air) |
IEC 61000-4-5 Surge for Bus |
Operating Temperature |
|---|---|---|---|---|---|---|
| AZRS8352P | 4.75-5.25 V | 118 kbps | ±13 V | ±30 kV / ±30 kV | ±30 A (8/20 µs) | -40 to 85 °C |
| AZRS5354P | 4.75-5.25 V | 8 Mbps | ±13 V | ±30 kV / ±30 kV | ±30 A (8/20 µs) | -40 to 85 °C |
Table 1. RS-485 Transceivers with System-Level ESD and Surge Protection
RS-485 Transceivers with High DC Bus-Fault Tolerance and High Operating Temperature:
Industrial environments commonly use 12-48 VDC power supplies. During equipment installation, fault repair, or commissioning, technicians may accidentally connect wiring incorrectly. If DC power is miswired to the RS-485 A/B bus and exceeds the maximum bus-fault voltage, communication errors or device damage may occur. With long cable runs, locating every damaged node can require considerable time. To address this risk, Amazing Microelectronic Corp. offers the AZRS7852P and AZRS9894P RS-485 transceivers with high DC bus-fault voltage protection. Both devices provide ±70 V DC tolerance on the A/B bus. Their main difference is the VCC range: the AZRS7852P supports 5 V logic applications, while the AZRS9894P supports a wide 3.3-5 V logic supply range. In addition, both devices operate from -40 to 125 °C, exceeding the temperature requirements of typical industrial-control products. Their key specifications are shown in Table 2.
| P/N | VCC |
Max. Data Rate |
Bus-Fault Voltage |
IEC 61000-4-2 ESD for Bus (Contact/Air) |
Operating Temperature |
|---|---|---|---|---|---|
| AZRS7852P | 4.75-5.25 V | 1 Mbps | ±70 V | ±8 kV / ±10 kV | -40 to 125 °C |
| AZRS9894P | 3.15-5.25 V | 1 Mbps | ±70 V | ±8 kV / ±10 kV | -40 to 125 °C |
Table 2. RS-485 Transceivers with High DC Bus-Fault Tolerance and High Operating Temperature
In summary, ESD, lightning-induced surges, and accidental DC miswiring can all damage equipment in ETC and industrial environments. Amazing Microelectronic Corp. provides RS-485 transceivers designed for these application scenarios. Please contact us if you have related requirements.
References:
[1] https://www.digitimes.com.tw/TECH/DT/N/SHWNWS.ASP?ID=0000490900_XC38A7WK1UZJ3ALSXML9K
[2] https://www.marketsandmarkets.com/Market-Reports/electronic-toll-collection-system-market-224492059.html
[3] http://news.c4it.tw/archives/78615