Programming Four
Different Rates
To program four groups of channels to scan at different rates we will use all
four scan lists. Our example:
–
scan channels 0 through 15, 300 times each second
–
scan channels 16 through 31, 150 times each second
–
scan channels 32 through 47, 50 times each second
–
scan channels 48 through 63, 10 times each second
We will define the minimum rate group, channels 0-63 in scan list 1. Scan
list 2 will be defined as channels 0-47. Scan list 3 will be channels 0-31.
Scan list 4 will be only channels 0-15. As you can see, the higher rate scan
lists are subsets of the lowest rate scan list.
The maximum rate is 30 times the minimum rate so we will need thirty
entries in
LISTL
.
LISTL
will reference the maximum rate group of channels
30 times and the min rate group only once. The group that is to be scanned
150 times per second will be referenced 15 times in
LISTL
(every other
scan). The group that is to be scanned 50 times each second will be
referenced 5 times (every sixth scan).
ROUT:SEQ:DEF LIST1,(@100:163)
Minimum rate group (*RST
default).
ROUT:SEQ:DEF LIST2,(@100:147)
150 Hz group.
ROUT:SEQ:DEF LIST3,(@100:131)
50 Hz group.
ROUT:SEQ:DEF LIST4,(@100:115)
Maximum rate group.
ROUT:SEQ:DEF LISTL,(@4,3,4,3,4,2,4,3,4,3,4,2,4,3,4,3,4,2,4,3,4,3,4,2,4,3,4,3,4,1)
Setting the
Absolute Scan Rate
So far we have only set relative rates that channels are measured. To set an
absolute channel scanning rate, we must control the interval between
execution of scan lists. To do this we use the trigger timer, so we select the
trigger timer as the trigger source:
TRIG:SOUR TIM
Trigger source is timer.
We then set the trigger interval using the
TRIGger:TIMer[:PERiod]
<
trig_interval
>
command. In our example we said that we want the highest rate
channels to be scanned 300 times each second. The trigger interval would then
need to be 3.3333 msec:
TRIG:TIM 3.3333ms
Scan list executed at 300 Hz.
To minimize time skew between the first and last channel in each scan list,
we will set the sample timer period as small as possible (10
µ
s):
SAMP:TIM LISTL,10us
Channel-to-channel pacing
10
µ
sec.
Chapter 4
Understanding the HP E1313/E1413 121
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