Rockwell-automation 1772-LP3 PLC - 2/30 Programmable Controller Progra Manual de usuario descargar pdf (Pagina 334)

Programming .01Second Timers

Appendix C

C3

Figure C.1

Timing

Diagram

Internal

Clock

Pulses

Enabled

Bit

Timed

Bit 15

Begin Timing

T = 3 2 < T < 3

One unit of time base

Example: [T

ON], Preset = 003; any time base

Note, too, that these timing accuracies refer only to internal

Mini-Processor operation. That is, these intervals refer to the length of time

which occurs between the moment that a timer is initialized (bit 17 set)

and the moment that the timed interval is complete (bit 15 set). Other

factors add to this timer inaccuracy. Chief among these are the response

time of the actual hardware devices controlled and monitored by the

Mini-Processor controller. (Refer to the section concerning Hardware and

Mini-Processor considerations, later on.)

You are urged not to overspecify timing accuracy. In many applications,

timing within 0.1 second will provide accuracy comparable to, or better

than, typical electromechanical timing relays. In general, you may apply

these rules:

for delays of 99 to 999 seconds, use the 1.0-second time base

for delays of 2.00 to 99.9 seconds, use a 0.1-second time base

for delays of 0.02 to 2.00 seconds, use the 10-msec time base

As an observation: when time delays are incorporated in a program to

provide a warmup or initializing period, or to prevent the simultaneous

application of power to high-current devices, inaccuracies on the order

of 50 to 250-msec are probably insignificant. For these uses, the 1.0- or

0.1-second time bases are more than adequate. Applications for the

10-msec timer are discussed on the next page.

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Rockwell-automation 1772-LP3 PLC - 2/30 Programmable Controller Progra Manual de usuario Pagina 334