Example: Data Turnaround Time

Description

The figure below shows an example of a control loop constructed to measure the data turnaround time at the field terminals of a pair of I/O bases.

A host PC running the test program is connected by Ethernet to two adapters with discrete I/O bases. The field output terminals of the output base are wired directly to the field input terminals of the input base. An oscilloscope is used to time the switching of the field signals.

Example: data turnaround time

The test program is a Java loop that performs this sequence:

continuously reads the input terminals of the input base module
writes an output terminal to a new (ON or OFF) condition
when a changed state is received from the inputs, toggles the outputs

Measurement Tests

The oscilloscope measures the time duration of the ON state of the outputs.

Data turnaround time measurement

Tests were conducted on two separate NT work stations with these configurations:

200 MHz, 96 MB RAM
100 MHz, 32 MB RAM

The table below shows the measured data turnaround times. The results indicate that the major factor affecting data timing is the speed of the loop execution in the host.

Results: data turnaround time

Networked Devices	Network Loading	Minimum Time	Maximum Time	Average Time	Host CPU Speed and RAM
2	10%	5 ms	9 ms	6.2 ms	200MHz 96 MB
2	40%	5 ms	9 ms	6.2 ms	200MHz 96 MB
2	70%	6 ms	9 ms	6.3 ms	200MHz 96 MB
64	10%	6 ms	8 ms	6.8 ms	200MHz 96 MB
64	40%	6 ms	12 ms	8.4 ms	200MHz 96 MB
64	70%	6 ms	13 ms	8.2 ms	200MHz 96 MB
64	10%	25 ms	30 ms	26.7 ms	100MHz 32 MB
64	40%	25 ms	30 ms	26.7 ms	100MHz 32 MB
64	70%	26 ms	30 ms	27.0 ms	100MHz 32 MB