I don't understand what you mean with "different sensors will be mixed up in the one series". Do you mean that there are two sensors and they take measurements at different times?
Here is what I would do. I assume you have a database table - let's call it "SensorsTbl". It contains measurement data taken by two sensors. There are fields "SensorA" and "DateA" for the sensor A measurements, "SensorA" is the value (e.g. a temperature), and "DateA" the date and time when the measurement was taken. Similarly, there are fields "SensorB" and "DateB" for the other sensor.
To establish a connection from the data in the db table "SensorsTbl" to the chart you must first add a TDatasource component and set its "Dataset" property to "SensorsTbl".
In order to display the data of SensorA you must add a series to the chart and a DBChartsource. Link the series to the DBChartSource by entering the DBChartSource in the property "Source" of the series. Then make these changes in the DBChartSource:
- Set "DataSource" to the TChartSource component that was added in the previous step
- Set "FieldX" to the "DateA" field of the db table (we will plot "Date" on the x axis)
- Set "FieldY" to the "SensorA" field (plot the values of column "SensorA" on the y axis).
- Since "DateA" contains date/time values activate the option dcsoDateTimeX.
Repeat with SensorB, i.e. add a second series and a second DBChartSource to the chart and link them like in the previous step. The only differences are that "FieldY" must be set to "SensorB", and "FieldX" to "DateB".
When the data table opens (SensorTbl.Open, or SensorTbl.Active := true) the chart must plot the data.
The x axis will be labelled by the date numbers, but not by the usual date strings. To fix this, add a TDateTimeIntervalChartSource and link it to the property Marks.Source of the BottomAxis, and set Marks.Style to smsLabel (you may have to add TAChartUtils to "uses", otherwise Lazarus will not find the identifier smsLabel).
In the attachment you can find a simple demo based on this description. In contrast to your requirement I am using a simple TMemoryDataset here for simplicity, and dummy data are created for both series in the OnCreate method of the form.