Real time sampling – Rockwell Automation 1771-IR , D17716.5.76 RTD INPUT MODULE User Manual
Page 27
Module Configuration
Chapter 5
5Ć3
The real time sampling (RTS) mode of operation provides data from a fixed
time period for use by the processor. 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 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 (msec) to 3.1 seconds in
increments of 100msec. Refer to Table 5.B below for actual bit settings. Note
that the default mode of operation is implemented by placing all zeroes in bits
13 through 17. In default mode, the sample time period is 50msec, and the RTS
time–out is inhibited. Note that binary representation of the RTS bit string is the
RTS period X 100msec. For example, 900msec = 01001 = (9 X 100msec).
Table 5.B
Bit Settings for the Real Time Sample Mode
Decimal Bits
Octal Bits
15
17
14
16
13
15
12
14
11
13
Sample Time Period
0
0
0
0
0
RTS inhibited (50msec)
0
0
0
0
1
100 ms
0
0
0
1
0
200 ms
0
0
0
1
1
300 ms
0
0
1
0
0
400 ms
0
0
1
0
1
500 ms
0
0
1
1
0
600 ms
0
0
1
1
1
700 ms
0
1
0
0
0
800 ms
0
1
0
0
1
900 ms
0
1
0
1
0
1.0 sec
0
1
1
1
1
1.5 sec
1
0
1
0
0
2.0 sec
1
1
0
0
1
2.5 sec
1
1
1
1
0
3.0 sec
1
1
1
1
1
3.1 sec
Important: Use decimally addressed bit locations for PLC-5 processors.
Real Time Sampling