MODBUS DATA ERROR

[evanh]

I haven't read this thread in detail so I maybe repeating a suggestion.

A 485 isolator is usually used at each field device in industrial environments simply for reliability, now and in the future, you never know when a machine is going to fault to earth and take every serially connected machine with it!  I can't remember an exact price but prolly between $US50 and $US100 per unit.


Evan

[ONG_FQ]

 

Dear Mr. / Mdm. / Ms. Support:

Did you have any more suggestions to solve this problem? We need to try our best to fulfill our customer requirement.

Thank You.

[support]

What you have is a system installation relation problem, not the PLC hardware problem since your installation regularly damages the PLC's RS485 driver as well as M2017P EEPRM. You have to address the problem at its root, or you have to use isolated network link such as fibre optic or optoisolated RS485 link. One possibiity would be to purchase isolated RS232 to RS485 converter at each PLC and convert the PLC's comm1 (RS232 port) to isolated RS485, then link this new isolated RS485 together to the master PLC. This should eliminate the electrical problem that you face whose cause are more likely related to noise, ground inbalance etc.

[FQ-ONG]

 

Dear Mr. / Mdm. / Ms. Support:

1)  Did you know how much our PLC (T100MD) can withstand from Electro Magnetic Interference(EMI) or Harmonic level? How much our PLC be able to bear or endure?

2)  On the Expansion Port, it have 4 pins that label:
a)  SD?
b)  CL
c)  LAT
d)  ?D
Can I connect this 4 pins to the ground?


Thank for your support.

[FQ-ONG]

Can the READMODBUS command generate the Host Link Command on the Slave PLC by itself?

Thank you.

[support]

NO. They are different commands. READMODBUS uses MODBUS ASCII or RTU protocol (depending on the port number use) while NETCMD$ uses the host link command protocol which is completely different from MODBUS.

[FQ-ONG]

Can the Electrical noise generate the Host Link Command on the Slave PLC?

Can we obstruct from Electrical noise to modifying either the RAM content or the EEPROM content or both by RS485?

Thank You.

[support]

Noise DO NOT generate any command. But if they are high voltage surges they can cause all kind of problems to 5V electronic circuit and can erase the content of EEPROM or even cause permanent damage.

[FQ-ONG]

May I know how the PLC protect itself away from outside interfere?

Good Luck!!!

[support]

I think your question is probably more like how YOU can protect the PLC from outside inteference?


The PLC is tested to withstand the following environmental stress:

a. Storage temperature: -20 to +85 degree C
b. Running temperature: 0 to 70 degree C.
c. Noise resistance: IEC801-4 (Fast transient)
    2KV to power supply, 50 microsecond pulse width,  1 minute
    1KV to I/O by capacitive coupling, 50 microsecond pulse width,
    1 minute.

These specs are usually good enough for most industrial applications without additional shielding. However, like all electronics devices if your environment contains high voltage spike, lightning strike, high energy electromagnetic pulses, high current noise generator such as VFD then you may have to take additional steps to shield them from such interference. This includes filtered power supply, grounded metal shield, separation of noise generator from control devices into different control panel - the usuall industrial practices.  

[FQ-ONG]

If RS232 read the data from DM[n] and the RS485 write the data into the same DM[n] at the same time, do it have any problem?

RS232 <--------- DM[1] <----------- RS485
RS232 <--------- DM[2] <----------- RS485

THANK YOU

[support]

It depends on which command is received first. If it receives a read command from a host computer on RS232, it will also complete the read command before processing a write command from RS485. The two command are handled one by one and there is no conflict.