BadIdentityTokenRejected is the answer an OPC UA server gives when the secure channel is up, the client certificate is trusted, and the session request arrives with no user in it, and on an S7-1500 with guest authentication off that is exactly where a first Python OPC UA client stops. It is the third of four … Read more
A Node-RED Logix tag read takes one install script, one palette install and two dialogs on a Raspberry Pi 4: Zone7_Speed from a 5069-L306ER appears in the debug sidebar as 30.0, and none of it involves typing a line of code. The node that does it is node-red-contrib-cip-ethernet-ip 1.1.3, installed from the palette manager, configured … Read more
At 02:30 on Sunday 25 October 2026 a logger in Berlin writes a row, and sixty minutes later it writes another row stamped 02:30, and the trend viewer draws the second hour on top of the first. Meanwhile the controller it reads from keeps its own idea of the time as a LINT of microseconds … Read more
48,000 rows is what a Raspberry Pi reading 20 tags a second has to hold through a 40-minute outage, and the SQLite file that held them in the run behind this article was 5.3 MB, including the write-ahead log. That is the size of the buffering PLC data problem, and it is small. What is … Read more
read_holding_registers(40011, count=2) comes back with exception code 02, read_holding_registers(11, count=2) decodes to -2.4e-41, and the 230.5 V the meter shows on its own display is sitting at address 10. That is the Modbus TCP register offset, and it is the fault everybody hits on their first evening with pymodbus 3.15.0 and a power meter on … Read more
A snap7 S7-1200 read – plc.db_read(12, 0, 12) against a CPU 1214C – returns twelve bytes on the bench and an exception on the machine, and the difference is two checkboxes in TIA Portal, neither of them on the Pi. python-snap7 3.1.2 talks the S7 protocol to TCP port 102 in pure Python, so there … Read more
Four lines of Python on a Raspberry Pi 4 read a CompactLogix tag – a REAL out of a 5069-L306ER – and nothing at either end is licensed. pycomm3 1.2.16 speaks EtherNet/IP to TCP port 44818 itself, which takes the OPC server, the Windows box it used to live on and the licence out of … Read more
200 tags at one row a second is 17.28 million rows a day, and at the 47 bytes a row that SQLite measured on this machine for a typed, indexed table, that is 814 MB a day and a 32 GB card full in 32 days. The same 200 tags logged on change, with a … Read more
A Docker Raspberry Pi that stopped logging on a Sunday had /var/lib/docker/containers/3f9a…/3f9a…-json.log at 22 GB when du got to it, and the file belongs to a container whose only job was to reconnect to a broker that had been down since Thursday. Docker’s default log driver is json-file, its default max-size is unlimited, and a … Read more
A pycomm3 write of 95.0 to Line4_SP on a CompactLogix comes back to the Raspberry Pi with no error, and the line is now running at 95 % because nothing between the driver and the tag asked whether it should. A read-only logger becomes a control path the first time somebody puts a slider on … Read more
The PLC does not run the model. What to publish, how the score returns as an advisory tag with a watchdog, and a pump anomaly detector on CompactLogix.