The CP series of PLC support clock functionality, this is enabled and retained when a backup battery is installed in the CPU unit. The clock is initially set via CX-Programmer.

Over time, it's natural for the clock to deviate or drift, this phenomenon is true for many electronic devices. If the PLC is not connected to an NTP (Network Time Protocol) server, then it has no way to synchronize the clock automatically. This is what many modern electronics use to ensure they all display the same time.

What is the expected deviation of the clock in the CP series PLC?

This value will differ, depending on the ambient temperature that the PLC is installed in, and the series of PLC. Select the series of PLC from the tabs below.

For most installations, the expected clock deviation would be around -2.0 to +2.0 minutes per month (approximately +/- 25 minutes a year). If the clock appears to deviate more than this, we would recommend checking when the battery was last replaced. 

The expected battery service life is approximately five years when installed in an environment where the ambient temperature is 25℃. Battery life will be reduced in higher temperatures. If it has been more than five years since the battery has been replaced, we would recommend replacing the battery in the PLC, even if the PLC isn't reporting a low battery voltage. The battery type used by the PLC can be found in the corresponding datasheet, alternatively, a list of batteries may be found here.

The battery replacement procedure can be found in the corresponding hardware manual, or operating manual.