The trend log object supports the following functions.
The trend data is saved continuously (ring buffer). When the available memory area is full, the oldest data is overwritten by new data. You can define the Continuous Run function with the parameter Stop when full.
The trend data is saved until the available memory area is full. You can define the buffer size [BufSize] within the range 2 to 5,000 entries. You can define the Single Run function with the parameter Stop when full.
The parameter Logging Type [LogTyp] defines the logging type. The values are:
- POLLED: Periodic Sampling
- COV: COV Sampling
- TRIGGERED: Triggered Sampling
By setting the parameters accordingly, you can define combinations of Continuous Run / Single Run and Periodic Sampling / COV Sampling / Triggered Sampling.
In Periodic Sampling data is acquired by sampling and storing values in a regular cycle. Periodic Sampling is supported by the trend log object and the trend log multiple object.
In COV Sampling data is stored based on a change of value (COV) of the referenced parameter. A COV subscription can be applied to all supported data types (analog, Boolean and multistate). The amount of change required to initiate a COV is set as a parameter in the object to be referenced. COV Sampling is supported only by the Trendlog object.
In Triggered Sampling an application (e.g., via data flow interconnection) determines when values are acquired/logged and saved. Triggered Sampling is supported by the Trendlog object and the Trendlog Multiple object.