Analog Signal to RS485/232 Converter

Published: Fri 06 Jun 2014
A blog entry by Anny Yu

Contributed by:

Anny Yu
Shenzhen WAYJUN Industrial Automation

Anny Yu's Blog



>> Analog signal acquisition, isolated RS-485/232 output

>> 12-bit AD converter, testing accuracy>0.1%

>> Can Program and calibrate modules accuracy via RS-485/232 interface

>> Three-port isolation (input/output/assistant power supply): 3000VDC

>> Wide power supply: 8~32VDC

>> High reliability, easy programming, easy installation.

>> Can program setting module address, baud rate

>> 0-5V voltage signal or 4-20mA current signal input

>> Supports Modbus RTU protocol

>> DIN35 Rail-mounted

Typical Application:                                                                     

>> Signal measurement/monitoring/control

>> RS-485 remote I / O, data acquisition

>> RS-232/485 bus industrial automation control system

>> Industrial field signal data acquisition and recording

>> Industrial field signal isolation and long-term transmission

>> Medical, industrial product development

>> 4-20mA or 0-5V signal acquisition

Product Overview:                                              Figure 1  WJ21

 WJ21 series products realize the signal acquisition between sensor and host, to measure analog signals. WJ21 products can be applied to RS-232/485 bus industrial automation control system,4-20mA / 0-5V signal measurement, monitoring and control,0-75mV ,0-100mV and other small-signal measurement and signal isolation and long-term industrial  transmission and so on.

Products include power supply isolation, signal isolation, linearization, A/D conversion and RS-485 serial communication. Each serial interface can connect up to 255 pieces WJ21 Series modules, communication using ASCII code or MODBUS RTU communication protocol, and its instruction set compatible with the ADAM modules, baud rate can been set by the code, with other manufacturers control module hang in the same RS-485 bus for easy programming.


WJ21 series products are based on SCM's intelligent monitoring and control system, users set the calibration value, address, baud rate, data format, checksum status, and configuration information are all stored in nonvolatile memory EEPROM.

 WJ21 products are according to industry standard design, isolation between signal input / output, can withstand voltage 3000VDC, high anti-interference ability and reliability. Operating temperature range is - 45 ~ +85 °C.

Function Description:

WJ21 signal isolation acquisition module can be used to measure one channel voltage or current signal,

 1. Analog signal input

 12-Bit acquisition accuracy, all products signal input range have been calibrated. In use, users also can program calibration easily.

 About the specific current or voltage input range, please see product selection.

 2. Communication protocol

   Communication Interface: one channel standard RS-485 communication interface, or one standard RS-232 communication interface, specify when ordering.

   Communication Protocols: supports two protocols, characters protocol of the command set defined and MODBUS RTU communication protocol. Can be programmed using the kind of communication protocol, can be achieved with PLC, RTU of many Brands or computer monitoring system for network communication.

   Data Format: 10 Bits. 1 start bit,8 data bits,1 stop bit.

       Address: (0 to 255) and baud rate (1200,2400,4800,9600,19200,38400 bps) can be set, the most long-distance about communication networks is up to 1200 meters, through the twisted-pair shielded cable.

 Communication interface of high anti-jamming design, ± 15KV ESD protection, communication response time is less than 100mS.

 3. Anti-jamming

 According to need to set the checksum. Module internal has transient suppression diodes, can inhibit a variety of surge pulse, protection module, and internal digital filter can also be well suppressed from the grid frequency interference.  

Product Selection:                                                                                

WJ21  U(A)     □ –  □

Input Voltage or Current Signal                     Interface

U10-5V           A10-1mA                  485: output is RS-485 interface 

   U20-10V          A20-10mA                 232: output is RS-232 interface

U30-75mV         A30-20mA            

  U40-2.5V          A44-20mA                         

   U50-±5V          A50-±1mA                         

   U60-±10V         A60-±10mA                         

   U70-±100mV      A70-±20mA

   U8user-defined     A8user-defined

Sample 1:    part No.:WJ21 A4-485   4-20mA input signal,output is RS485 interface

Sample 1:    part No.:WJ21 U1-232   0-5V input signal,output is RS232 interface

General parameters:

 (typical @ +25 ℃, Vs to 24VDC)

 Input type: Input current / voltage input

 Accuracy: 0.1%

 Temperature drift:± 30 ppm / ℃ (± 50 ppm / ℃, maximum)

 Input Resistance: 50Ω (4-20mA/0-20mA/0- ± 20mA current input)

              100Ω (0-10mA/0- ± 10mA current input)

              1KΩ (0-1mA/0- ± 1mA current input)

              >1MΩ(voltage input)

Bandwidth:  -3 dB 10 Hz

Conversion rate: 10 Sps

Common Mode Rejection (CMR): 120 dB (1kΩ Source Imbalance @ 50/60 Hz)

Normal Mode Rejection (NMR): 60 dB (1kΩ Source Imbalance @ 50/60 Hz)

Input Protection: over-voltage protection, over-current protection

Communication: RS-485 protocol or RS-232 standard characters protocols and MODBUS RTU communication protocol

              Baud Rate (1200,2400,4800,9600,19200,38400 bps) can be selected via software

Address (0 to 255) can be selected via software

Communication Response Time: 100 ms maximum

Power Supply: +8 ~ 32VDC wide range power supply, internal anti-reverse and over-voltage protection circuit

Power Loss: less than 1W

Operating Temperature: - 45 ~ +80 ℃

Humidity: 10 ~ 90% (no condensation)

Storage Temperature: - 45 ~ +80 ℃

Storage Humidity: 10 ~ 95% (no condensation)

Isolation Voltage: input / output: 3KVDC, 1 minute, leakage current:1mA

              Which output signal and power supply are common ground.

Shock Voltage: 3KVAC, 1.2/50us (peak)

Dimensions: 106.7 mm x 79 mm x 25mm