A Siemens KTP 700 Basic PN connected to a LOGO controller may appear to refresh continuously when an HMI switch or variable briefly accepts a value and then returns all variables to their defaults. In the documented case, communication was established and the application had worked before a project change.
Identify the Reset Pattern
The defining symptom is an immediate reset after writing a value: setting a variable to 1 or operating a switch causes both input and output variables to return to their default values. Because the connection remained established, the investigation focused on project configuration rather than treating loss of communication as the confirmed cause.
Check the LOGO Block Configuration
The confirmed cause was a Network Analog Output block configured for Local Variable Memory. Changing that block to Remote Device stopped the variable refresh problem.
| Network Analog Output setting | Observed result |
|---|---|
| Local Variable Memory | HMI writes were immediately replaced and variables returned to default values. |
| Remote Device | The reported variable reset behavior stopped. |
Correct and Verify the Project
- Confirm that the KTP 700 Basic PN connection to the LOGO controller is established.
- Open the LOGO project and locate the Network Analog Output block associated with the affected data.
- Change its destination from Local Variable Memory to Remote Device.
- Apply the updated project and operate the HMI switch or write
1to the test variable. - Verify that the written value remains active instead of immediately returning to its default.
If the reset remains, compare the existing application with a new minimal test program and test another HMI to separate project behavior from a possible panel hardware problem. These are isolation tests; the evidence confirms the block-setting correction only for the documented case.
FAQ
Why does my KTP 700 Basic keep resetting variables?
In the documented KTP 700 Basic PN and LOGO application, a Network Analog Output block was set to Local Variable Memory. Selecting Remote Device stopped the resets.
Which LOGO setting fixes KTP 700 Basic variable refresh?
Locate the affected Network Analog Output block and change its destination from Local Variable Memory to Remote Device, then retest the HMI write.
How do I verify the KTP 700 Basic reset problem is fixed?
Operate the affected switch or write 1 to a test variable. Confirm that the value remains active rather than immediately returning to its default.