Real time sampling – Rockwell Automation 1771-IR Series D RTD Input Module User Manual User Manual
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Configuring Your RTD Module
Publication 1771Ć6.5.129 - March 2000
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 (ms) to
3.1 seconds in increments of 100ms. Refer to the table 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 50ms, and the RTS time–out is
inhibited. Note that binary representation of the RTS bit string is the
RTS period X 100ms. For example, 900msec = 01001 = (9 X
100ms).
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 (50ms)
0
0
0
0
1
100ms
0
0
0
1
0
200ms
0
0
0
1
1
300ms
0
0
1
0
0
400ms
0
0
1
0
1
500ms
0
0
1
1
0
600ms
0
0
1
1
1
700ms
0
1
0
0
0
800ms
0
1
0
0
1
900ms
0
1
0
1
0
1.0s
0
1
1
1
1
1.5s
1
0
1
0
0
2.0s
1
1
0
0
1
2.5s
1
1
1
1
0
3.0s
1
1
1
1
1
3.1 sec
Important: Use decimally addressed bit locations for PLC-5 processors.
Real Time Sampling