Node-red-contrib-s7

Industrial
1

Dear All,
Could please let us know the limitations of Tags (in numbers) configured to S7 1200 PLC with scan rate of 1 Second.

2

Hi, why dont you try adding tags until you start seeing issues.

A bit of advice...

Instead of polling (for example) 100 INT tags at 1sec each, it is FAR more economical to poll 1 tag with 200 bytes then convert the values to whatever you need at node-red side.

For example you could arrange your PLC logic to put all items of interest into an array then read that array in 1 go. The benefits are 2 fold...

  1. you could probably achieve a poll time of 100ms or less
  2. data is consistent (meaning all values are read from the same PLC scan)

If the data types are different, you can use node-red-buffer-parser to parse the byte values back into INT16/UINT16/INT32/UINT32/STRING etc etc etc

3

Hi,
It is not possible to put PLC logic in array concept because tag will be addresses by different-different DB area. Hence it would be good idea to know the Tag limitation in Node-red.

4

You can write simple ladder or ST to copy the values into a single DB then read them all in one hit. This is a common practice in plcs especially when consistent data is required.

If you want to know that you're going to have to experiment.

1 Like
5

i know adding tag and perform testing would be the best option to know the limitation. I thought if some one having this answer would be time saver.

6

That depends on many many things (ethernet speed, processor speed, network bandwidth, variables sizes).
The library has also an algorithm to optimize the reading speed, so for example,
if you request DB1 address 10 and DB1 address 12, the library will request DB1 address 10 to 12, so that it is not necessary to make 2 requests.
All of this makes it impossible to calculate what your are requesting.

7

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