Real time sampling – Rockwell Automation 1771-IFE , D17716.5.90 USER MNL. ANALOG INPUT Module User Manual
Page 34
Module Configuration
Chapter 4
4-5
The real time sampling (RTS) mode of operation provides data gathered at
precisely timed intervals for use by the processor. BTW word 3 bits 11–15
(13–17 octal) are used to set the real time sampling interval.
RTS is invaluable for time based functions (such as PID and totalization) in
the PLC. It allows accurate time based calculations in local or remote I/O
racks. In the RTS mode the module scans and updates its inputs at a user
defined time interval (T) instead of the default interval. The module
ignores block transfer read (BTR) requests for data until the sample time
period elapses. The BTR of a particular data set occurs only once at the
end of the sample period and subsequent requests for transferred data are
ignored by the module until a new data set is available. If a BTR does not
occur before the the end of the next RTS period, a time-out bit is set in the
BTR status area. When set, this bit indicates that at least one data set was
not transferred to the processor. (The actual number of data sets missed is
unknown.) The time-out bit is reset at the completion of the BTR.
Set appropriate bits in the BTW data file to enable the RTS mode. You can
select RTS periods ranging from 100 milliseconds (ms) to 3.1 seconds.
Refer to Table 4.E below for actual bit settings. Note that the default mode
of operation is implemented by placing all zeroes in bits 11–15
(13–17 octal).
Table 4.E
Bit Settings for the Real Time Sample Mode
Decimal Bits 15
14
13
12
11
Sample Time Period
15
14
13
12
11
Sample Time Period
Octal Bits
17
16
15
14
13
Sample Time Period
17
16
15
14
13
Sample Time Period
0
0
0
0
0
No RTS, Default settings
1
0
0
0
0
1.6s
0
0
0
0
1
100ms
1
0
0
0
1
1.7s
0
0
0
1
0
200ms
1
0
0
1
0
1.8s
0
0
0
1
1
300ms
1
0
0
1
1
1.9s
0
0
1
0
0
400ms
1
0
1
0
0
2.0s
0
0
1
0
1
500ms
1
0
1
0
1
2.1s
0
0
1
1
0
600ms
1
0
1
1
0
2.2s
0
0
1
1
1
700ms
1
0
1
1
1
2.3s
0
1
0
0
0
800ms
1
1
0
0
0
2.4s
0
1
0
0
1
900ms
1
1
0
0
1
2.5s
0
1
0
1
0
1.0s
1
1
0
1
0
2.6s
0
1
0
1
1
1.1s
1
1
0
1
1
2.7s
0
1
1
0
0
1.2s
1
1
1
0
0
2.8s
0
1
1
0
1
1.3s
1
1
1
0
1
2.9s
0
1
1
1
0
1.4s
1
1
1
1
0
3.0s
0
1
1
1
1
1.5s
1
1
1
1
1
3.1s
Default Settings =
SingleĆended inputs Ć 25 ms
Differential inputs Ć 12.5 ms
Real Time Sampling