FAQ

Modbus wiring

 

Modbus is one kind of protocols that machine can transfer data through this method. Generally speaking, MODBUS is to machines what language is to human beings. Communication protocol is software level protocol, and different devices exchange data through the same protocol. Then machine needs physical port to transfer data, such as EIA 485(RS485)、EIA422(RS422)、EIA232(RS232) or RJ45 Ethernet.

QA-E-4-1.png

 

Attention:Device with RS485 port does not mean it must support Modbus Protocol. Please contact Device provider for more information.

 

1.Different device provider has different sign:

RS422 4 wires

Receive+  RX+  RDB  RDB+ 
Receive-  RX-  RDA  RDA-
Transmit+  TX+  SDB  SDB+
Transmit-  TX-  SDA  SDA-

 

RS485 2 wires

Receive D-
RS485- 
RX-
TX- 
RDA
SDA 
RDA-
SDA- 
 Transmit D+
RS485+
 RX+
TX+
 RDB
SDB
 RDB+
SDB+
 B

 

2.Connection diagram:

QA-E-5.png

 

3. Examples:

QA-E-6.png

 

 

1. Make sure the principle of connection is correctly when do wiring, and do not use T type wiring method, star type wiring method or any other wiring method for convenience.

QA-E-7.png

 

2. Keep away from high noise source when wiring. Do not use the same groove as the power wire uses in the distribution box. Externally, keep as far away as possible from devices which have electric magnetic radiation. The transfer wire need to use shielded twisted par wire. Normal twisted pair wire can be used when conducting short distance communication in low noise environment to reduce cost. But in high noise environment, long distance communication or in case of high communication quality is required, the dedicated transfer wire for RS-485 is recommended. It may make higher budget, but the communication quality will be improved magnificently.

QA-E-8.png

 

3. Terminal resistances must be parallel connected to the two terminal points of the whole communication circuit. For the twisted pair wire used by RS-485 interface, the terminal resistances should choose 120 Q 1/2 W ones.

QA-E-9-1.png

 

 

Final check before transmitting data

 

1. Check whether the communication software is working properly, including whether the communication parameters (such as ID, baud rate, check bit, delay, time-out setting) are correctly.
2. Reduce environmental interferences.
3. Re-wire the transfer wire, and avoid noise source.
ID:ID can only be identical.
Baud、Parity Check Bit:Ever part of system setting should be same.
Delay Time:Short delay time interval may cause data lose.
Time out:1000~500ms are recommended, depending on devices.

If everything on the system is done correctly and communications still do not work, please contact PLC provider for more PLC communication setting details.

How to install NPN/PNP transducer on PLC?

 

  • General PLC (Programmable Logic Computer) could select input type NPN or PNP, by connects S/S to 24V or 0V respectively.
    • NPN input:S/S connects to 24V.
    • PNP input:S/S connects to 0V.

          QA-E-2-1.png

           Attention:Please notice that GND of external power shall be connected to GND of PLC. 

 

  • Considering PLC power supply ability, please apply external power to sensors rather than internal power of PLC.Please refer to the figure below:

          QA-E-3-1.png

 

The LED flashes and turns off: Check whether the loading current is too high.

  • Yes:
    • a. Exchange magnetic switch with larger rated operating voltage, current, and contact rating.
    • b. Use relay or PLC to drive the load indirectly.
  • No: Please send back for examination.

Magnetic switch operates twice continuously:

  • Since the magnetic field of magnet is too strong or the sensitivity of magnetic switch is too high. Please contact to our RD department.

Contact point is unbreakable: Check whether the magnetic switch is overloaded.

  • No: Check the wire distance between the magnetic switch and the load is more than 10M or not.
    • Over 10M:Add an inductor (About 1000uH) to eliminate to capacitor impulse caused by long wiring.
    • Below 10M: Please send back for examination.
  • Yes:
    • a. Exchange magnetic switch with larger rated operating voltage, current, and contact rating.
    • b. Use relay or PLC to drive the load indirectly.
Page 1 of 2

The LED on magnetic switch does not work: Check power supply type (AC or DC) of product

  • AC-powered product:
    • Switch works:LED is out of order. Please send back for examination.
    • Switch doesn’t work:Please refer《The Malfunction of Magnetic Switch》
  • DC-powered product:
    • Switch works:Check the polarity of wiring
      • Wrong:Please correct it.
      • Correct:Please send back for examination.
    • Switch doesn’t work:Please refer《The Malfunction of Magnetic Switch》

The Malfunction of Magnetic Switch: Check wiring

  • Correct: Remove magnetic switch from cylinder, and use a magnet to test the switch.
    • Switch works: the magnetic field of the magnet inside the cylinder is not
      • enough or the sensitivity of magnetic switch is too weak.
      • Please contact our RD department.
    • Switch doesn’t work: Please send back for examination.
  • Wrong: Please correct it.

Contact point is unbreakable: Check whether the magnetic switch is overloaded.

  • No: Check the wire distance between the magnetic switch and the load is more than 10M or not.
    • Over 10M:Add an inductor (About 1000uH) to eliminate to capacitor impulse caused by long wiring.
    • Below 10M: Please send back for examination.
  • Yes:
    • a. Exchange magnetic switch with larger rated operating voltage, current, and contact rating.
    • b. Use relay or PLC to drive the load indirectly.

The LED flashes and turns off: Check whether the loading current is too high.

  • Yes:
    • a. Exchange magnetic switch with larger rated operating voltage, current, and contact rating.
    • b. Use relay or PLC to drive the load indirectly.
  • No: Please send back for examination.

Magnetic switch operates twice continuously:

  • Since the magnetic field of magnet is too strong or the sensitivity of magnetic switch is too high. Please contact to our RD department.

How to install NPN/PNP transducer on PLC?

 

  • General PLC (Programmable Logic Computer) could select input type NPN or PNP, by connects S/S to 24V or 0V respectively.
    • NPN input:S/S connects to 24V.
    • PNP input:S/S connects to 0V.

          QA-E-2-1.png

           Attention:Please notice that GND of external power shall be connected to GND of PLC. 

 

  • Considering PLC power supply ability, please apply external power to sensors rather than internal power of PLC.Please refer to the figure below:

          QA-E-3-1.png

 

Modbus wiring

 

Modbus is one kind of protocols that machine can transfer data through this method. Generally speaking, MODBUS is to machines what language is to human beings. Communication protocol is software level protocol, and different devices exchange data through the same protocol. Then machine needs physical port to transfer data, such as EIA 485(RS485)、EIA422(RS422)、EIA232(RS232) or RJ45 Ethernet.

QA-E-4-1.png

 

Attention:Device with RS485 port does not mean it must support Modbus Protocol. Please contact Device provider for more information.

 

1.Different device provider has different sign:

RS422 4 wires

Receive+  RX+  RDB  RDB+ 
Receive-  RX-  RDA  RDA-
Transmit+  TX+  SDB  SDB+
Transmit-  TX-  SDA  SDA-

 

RS485 2 wires

Receive D-
RS485- 
RX-
TX- 
RDA
SDA 
RDA-
SDA- 
 Transmit D+
RS485+
 RX+
TX+
 RDB
SDB
 RDB+
SDB+
 B

 

2.Connection diagram:

QA-E-5.png

 

3. Examples:

QA-E-6.png

 

 

1. Make sure the principle of connection is correctly when do wiring, and do not use T type wiring method, star type wiring method or any other wiring method for convenience.

QA-E-7.png

 

2. Keep away from high noise source when wiring. Do not use the same groove as the power wire uses in the distribution box. Externally, keep as far away as possible from devices which have electric magnetic radiation. The transfer wire need to use shielded twisted par wire. Normal twisted pair wire can be used when conducting short distance communication in low noise environment to reduce cost. But in high noise environment, long distance communication or in case of high communication quality is required, the dedicated transfer wire for RS-485 is recommended. It may make higher budget, but the communication quality will be improved magnificently.

QA-E-8.png

 

3. Terminal resistances must be parallel connected to the two terminal points of the whole communication circuit. For the twisted pair wire used by RS-485 interface, the terminal resistances should choose 120 Q 1/2 W ones.

QA-E-9-1.png

 

 

Final check before transmitting data

 

1. Check whether the communication software is working properly, including whether the communication parameters (such as ID, baud rate, check bit, delay, time-out setting) are correctly.
2. Reduce environmental interferences.
3. Re-wire the transfer wire, and avoid noise source.
ID:ID can only be identical.
Baud、Parity Check Bit:Ever part of system setting should be same.
Delay Time:Short delay time interval may cause data lose.
Time out:1000~500ms are recommended, depending on devices.

If everything on the system is done correctly and communications still do not work, please contact PLC provider for more PLC communication setting details.

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