ISOAD A4-485 Loop-Powered 4-20mA to RS485 Isolated Converter

SunYuan  The ISOAD A4-485 is a low-cost, compact, passive programmable bus communication intelligent isolation data acquisition module. It adopts a two-wire loop-powered design. The module can convert 4–20mA analog signals from instrumentation and sensor transmitters within the signal transmission loop into digital data through ADC conversion, and then linearly map the signals according to the configured measurement range before transmitting them to the host system for data acquisition and reading.This IC features reverse polarity and over-current protection, making it suitable for the digital and intelligent upgrade of various traditional legacy transmitters and instrumentation equipment used in industrial fields.It is widely applied in industries such as oil & gas, chemical, environmental monitoring, and mining for intelligent monitoring of process control points including temperature, pressure, flow, and level.In most industrial applications, sensors are used to convert physical quantities such as temperature, pressure, flow, and rotational speed into analog current signals. These signals are then processed by this data acquisition IC for isolation amplification and analog-to-digital conversion, and subsequently transmitted to control instruments, PLC/DCS systems, or host computers for remote measurement and control.

The ISOAD A4-485 adopts a two-wire loop-powered wiring method. It is designed for the isolation, transmission, and acquisition of standard 4–20mA analog signals between sensors, transmitters, and PLC/DCS systems.The module requires no external power supply; it is directly connected in series within the field 4–20mA current loop.Through software configuration, users can set parameters such as zero point, full scale range, alarm output control, and delay functions.The module uses high-speed isolation technology to achieve 3000VDC isolation between the current loop input and the RS485 communication bus, ensuring that sensors and host systems do not interfere with each other, providing safe and reliable operation.

The ISOAD A4-485 supports RS485 communication, enabling remote connection to PLCs or HMIs for reading measured values. It also allows configuration and modification of related parameters such as module address, baud rate, measurement range, and alarm thresholds. Alarm status can be read via registers.

The internal input signal has a linear relationship with the acquired readback value. The full-scale range can be configured from -60000 to 60000. For example, when the input signal is 4–20mA, the corresponding acquisition range is 4000–20000. The linear mapping relationship is as follows: 4mA corresponds to a reading of 4000, 12mA corresponds to 12000, and 20mA corresponds to 20000.