Rockwell-automation 1746-HSCE2 Multi-Channel High Speed Counter Module Manual de usuario descargar pdf (Pagina 30)

Publication 1746-UM002B-EN-P - August 2004

2-10 Module Operation

Ring Counter

Figure 2.6 demonstrates ring counter operation. In ring counter

operation, the count value changes between programmable minimum

and maximum values. If, when counting up, the counter reaches the

maximum value, it rolls over to the minimum value. If, when counting

down, the counter reaches the minimum value, it rolls over to the

maximum value.

Figure 2.6 Ring Counter Diagram

Rate Value

The rate value reported to the processor is calculated in counts per

second (Hz), and is available with all input configurations. The input

configuration determines how the rate value is calculated. When the

count value is increasing, the rate value is positive. When the count

value is decreasing, the rate value is negative.

The rate value is generally calculated as follows:

When the first input pulse is received, the value of an independent,

free-running timer (Ta) is recorded. The module waits approximately

16 ms, while counting more input pulses. After 16 ms, the module

waits for the next input pulse, and the value of the independent timer

(Tb) is again recorded. The module then calculates the rate value

using the formula:

Rollover

Count Up

Count Down

Maximum Value

Minimum Value

rate value

number of counts

Tb Ta–

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Rockwell-automation 1746-HSCE2 Multi-Channel High Speed Counter Module Manual de usuario Pagina 30