Writing variables with OPC UA

Question

Recently I was trying to communicate with a Siemens S7-1200 plc, I am using the OPC UA protocol, I am able to connect and read all the variables but I have problems when I try to write a value in the variable, this is the error message:

File "c:\Users\User\Documents\Python\OpcUa\Client_PLC.py", line 18, in <module>
Plc.set_values(var_2,val)
File "C:\Python310\lib\site-packages\opcua\client\client.py", line 670, in set_values
nodeids = [node.nodeid for node in nodes]
TypeError: 'Node' object is not iterable

And this is the code I am trying.

from opcua import Client
import time
   
url = "tcp.upc://192.168.0.1:4840"

val = 2

Plc = Client(url)

Plc.connect()


while True  :
    var = Plc.get_node("ns=4;i=2")
    print ("The value is : {}".format(var.get_value()))
    var_2 = Plc.get_node("ns=4;i=3")
    print(var_2)
    Plc.set_values(var_2,val)
    time.sleep(2)

Update:

I've tried to use set_value command but I get this error code:

opcua.ua.uaerrors._auto.BadWriteNotSupported: "The server does not support writing the combination of value, status and timestamps provided."(BadWriteNotSupported)

Schroeder · Accepted Answer · 2022-01-24T09:12:42.493

0

You use the function set_values which expects a list of nodes. Try this instead:

val.set_value(var_2)

If the plc returns an error set only the value:

val.set_value(DataValue(var_2))

edited Jan 24 '22 at 09:12

answered Jan 21 '22 at 06:53

Schroeder

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score 0 · Answer 2 · answered Jan 22 '22 at 01:11

I've tried to use set_value command but I get this error code: opcua.ua.uaerrors._auto.BadWriteNotSupported: "The server does not support writing the combination of value, status and timestamps provided."(BadWriteNotSupported)

While it's possible this server is indicating it does not support writes to this Node at all, most commonly I've found that it means the server does not support writing a StatusCode and/or timestamps along with a value inside the DataValue your client is sending.

Writing variables with OPC UA

2 Answers2