Delta RMC101 Manual do Utilizador descarregar pdf (Página 884)

100

101

RMC100 and RMCWin User Manual

D-22

T is the sample period (control loop time)

Suppose that the sample period (control loop time) is 1 millisecond, the transducer returns one

count for every thousandth of an inch, and the axis is moving at 4.8 inches per second (4800

counts/s).

As the controller samples the position each control loop, it will see the position change by either 4

or 5 position units, but never the actual rate of 4.8, because the transducer returns a fixed

number of counts. Therefore, when these values are divided by 0.001 seconds, the computed

Actual Speed will jump back and forth between 4000 and 5000, but will never show any value

between.

The situation improves with higher speeds and higher-resolution transducers, but worsens with

lower speeds and lower-resolution transducers. Filtering can be applied to smooth out the Actual

Speed, as the RMC does, but the filtering must be limited to avoid smoothing out real changes in

the Actual Speed.

D.2.10 NULL DRIVE

This field displays the amount of drive in millivolts that it takes to hold the Actual Position at the

Target Position while at rest. Ideally this number should be zero if the valve is perfectly nulled.

In RMC100 CPU firmware versions earlier than 19980414, this field is automatically updated

toward the Integral Drive when the Actual Position is exactly equal to the Command Position and

the speed is zero. However, in later versions this feature was removed in favor of allowing the

user to manually update the NULL DRIVE using either the Set Null Drive, Set Null Drive to

Integral Drive, or Restore Null Drive commands.

This field is only used in Open Loop Mode. NULL DRIVE is added to the drive output.

Why Bother?

The NULL DRIVE field can be used to null valves and drives. Usually there is a null or offset

adjustment on the valve or amplifier that can be adjusted so the NULL DRIVE is 0.

D.2.11 STEP

This field shows the current step the axis is executing of the 256 steps in the Event Step Table.

This is valid only when Event Control is being used. Use this field in conjunction with the Link

Value status word to monitor the progress of an axis through the step table.

D.2.12 LINK VALUE

This field is used only when the axis is using the Event Step Table. It represents the current event

step link value of the current step for the axis. The current step is displayed in the STEP status

word.

1 2 ... 879 880 881 882 883 884 885 886 887 888 889 ... 950 951

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