riandanualdy

HMI and Weighing Indicator

7 posts in this topic

hallo, i have problem here.

i want to connect HMI OMRON NB7W-TW00B to weighing indicator with Modbus RTU rs485.

i use this link https://www.myomron.com/index.php?action=kb&article=1538 for wiring diagram for rs485.

and the baudrate, databit, parity check and stop bit is same between HMI and weighing indicator.

but the output in HMI is "[2] PLC No Response: 00-01-2" i think the problem is my rs485 connection.

can you help me? thank you.

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Not an Omron user but having had a look at the link it may be something simple.  So playing devils advocate can you confirm that the PLC is on COM1 of the HMI and the Weigher on COM2.

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13 hours ago, whyme said:

Not an Omron user but having had a look at the link it may be something simple.  So playing devils advocate can you confirm that the PLC is on COM1 of the HMI and the Weigher on COM2.

i try use com 1 to PLC omron and its working, but i want to try com 2 to connect to weighing indicator via modbus RTU rs485 but the output is "2] PLC No Response: 00-01-2"

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All of the info I have seen so far on line shows a PLC or a network of PLC's on COM2.  It being a HMI it would have to connect to something intelligent downstream so my question to you is, is the HMI configurable for non PLC connection?  It may only be linkable to PLC's and as you have not connected a PLC on com2, it is shouting at you. 

Second question. Has the HMI got a driver for the weighing device, or does the weighing device have an OMRON PLC emulation mode?

That's all I have I am afraid.  I came across this ...

https://www.myomron.com/index.php?article=1535&action=kb

... in my on line travels.  It may have a pointer for you.  Sorry I don't have a definitive answer for you.

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1 hour ago, whyme said:

All of the info I have seen so far on line shows a PLC or a network of PLC's on COM2.  It being a HMI it would have to connect to something intelligent downstream so my question to you is, is the HMI configurable for non PLC connection?  It may only be linkable to PLC's and as you have not connected a PLC on com2, it is shouting at you. 

Second question. Has the HMI got a driver for the weighing device, or does the weighing device have an OMRON PLC emulation mode?

That's all I have I am afraid.  I came across this ...

https://www.myomron.com/index.php?article=1535&action=kb

... in my on line travels.  It may have a pointer for you.  Sorry I don't have a definitive answer for you.

nah im not sure about that, but in this link https://www.myomron.com/index.php?action=kb&article=1538 and https://www.youtube.com/watch?v=SFnNvZmEWX8 , HMI NB7W can connect to non plc. i just want to try connect my weighing indicator connect to HMI because im doing research about weighing indicator.

thank you

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No Probs - good luck

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I have no experience with Omron, but from general Modbus experience I have these observations:

1) Master or slave?

a) Modbus functionality is sometimes 'native', included in the operating system, but is frequently an option, meaning not every device has Modbus, only those with an option.  Do each device have the Modbus functionality?    Does each device really talk Modbus (not some other protocol over RS-485)?

b) A Modbus master can talk to one or more Modbus slaves, a Modbus master can not talk to a Modbus master.    

c)  An RS-485 network can support one and only one Master

d)  Field devices that are Modbus slaves will always have a 'map' or table' of assigned register addresses where the data resides.  Modbus masters do not have a map or table.

e)  Some PLC's can operate as either a Modbus master or a Modbus slave, depending on programming and port assignment.  

All that said, a Modbus master does not have a Modbus slave node ID number (1-247), also called station number.   A Modbus slave node ID number (station number) indicates slave functionality, not Master functionality.

In the link you provided (for NB7W), the PLCs are functioning as Modbus slaves, as evidenced by two PLCs on one Comm port and each has a 'station number'.  Only a Modbus slave would have a station number.  Modbus Masters do not have station numbers.  

Presumably the NB7W is a Modbus master, which is typical for HMI devices when used with PLCs.

That means your weighing indicator must be a Modbus slave to communicate to HMI (a Modbus master) as shown in the setup in the NB7W link provided. 

However, generic digital indicators typically have a Modbus slave 'option', although Precision Digital makes a "Modbus indicator" that can be a Modbus master.   I do not know the typical functionality of a 'weighing indicator'.

If you want to connect the HMI, a Modbus master, to your weighing device then your weighing device must be a Modbus slave.

Is your weighing indicator a Modbus slave?


2)  RS-485 issues

a)  The drive lines for RS-485 differ in labeling from manufacturer to manufacturer.  While, electrically, (+) wires to (+) and (-) wires to (-), sometimes one manufacturer's (+) is the other manufacturer's (-).   Connecting the drivers backwards will not damage the lines, but RS-485 (and Modbus) will not function.  

Try swapping the lines to see if the lines are labeled differently.

b)  RS-485 should have a 3rd wire, a signal ground.   But many manufacturers do not supply a signal ground connection.

c)  Termination resistors (typically 120 ohms) are installed at the devices on the two ends of the network, usually the master and then the last slave.  Short cable lengths at low baud rates (9600, 19.2K) will almost always work without resistors.

d)  Just the presence of an RS-485 port does NOT mean that the device talks Modbus.  Modbus is a protocol, RS-485 is a communication link.  If a device talks modbus, its documentation will specifically state Modbus functionality. 

3)  The Modbus master has to be configured/programmed to poll for the data from the slave

Have you configured the HMI to poll the weigh indicator for the data?

Edited by DanW
just realized goal is to connect HMI to weighing indicator, not PLC to weighing indicator

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