Detailed description

Selecting the operating modes

Two operating modes can be selected through the TR_S parameter input.

Operating mode	TR_S
Automatic	0
Tracking	1

Automatic operating mode

In the automatic mode, the function block operates according to the following rules:

If	Then
Cycle time > T_DELAY/128	If the current IN value is transferred to the buffer, the oldest IN value will be displayed on the output OUT. In this case the solution is smaller than 128 and there is a systematic error, i.e. some IN values are saved twice (see also example).
Cycle time < T_DELAY/128	not all IN values can be contained in the buffer. In this case the IN value is not saved in some cycles and OUT remains unchanged in this cycle.

Example of cycle time > 128

The following values are accepted:

Cycle time = 100 ms

T_DELAY = 10 s

tin = T_DELAY / 128 = 78 ms

As tin (reading time) is shorter than the cycle time, every IN value is accepted in the buffer. On the fourth performance of the function block (after 400 ms) the IN value will be saved twice rather than once (because 3 x 78 = 312 and 4 x 78 = 390).

Tracking mode

In the tracking mode, the tracking value TR_I is transmitted permanently to the output OUT. The internal buffer is filled with the tracking value TR_1. The buffer is marked as charged (READY =1).

Example of the behavior of the QDTIME

The diagram shows an example of the behavior of the function block. The input IN changes, in the form of a ramp, from one value to a new value and the output OUT follows the input IN, delayed by the deadtime T_DELAY.

Diagram of the QDTIME function block.