Analog input module SM 331; AI 6 x TC Isolated (6ES7331‑7PE10‑0AB0)
A5E02398493-02, 11/2008
17
This is only an example. The logic and used memory must be adjusted to the structure of the used PLC program.
The return value of the SFC "WR_REC" (MW 22) can be evaluated according to the structure of the used PLC program. For
further information refer to the "SIMATIC System Software for S7-300/400 System and Standard Functions".
Startup behavior and compensation watchdog when using external reference cold junction compensation via remote RTD
Upon module startup, all inputs will report full scale, 32767. Upon receiving a compensation value via DS2, the module will
begin to read the TC inputs and report proper data. If the module does not receive DS2 within 5 minutes after startup, a
reference channel fault will be reported in the standard channel diagnostic data and a diagnostic interrupt will be sent if
enabled.
The module contains a 5 minute watchdog timer which is reset upon receiving a new compensation value via DS2. If during
normal operation the module does not receive DS2 before the 5 minute watchdog timeout, a reference channel fault will be
reported in the standard channel diagnostic data and a diagnostic interrupt will be sent if enabled.
Internal runtime calibration
The module can compensate for most of the temperature drift errors of the internal hardware. The internal runtime
calibration is always performed on startup, parameterization, and power cycle. If enabled by parameters, the internal runtime
calibration can also be performed upon ambient temperature changes in the module of 5 degree C. Enabling the runtime
calibration will cause an interruption of the I/O cycle for the module until the calibration is complete. The interruption time
varies due to the interference frequency selected in parameters and is provided in the following table.
Runtime calibration interruption time
Interference Frequency Interruption Time
10 Hz 600 ms
50 Hz 120 ms
60 Hz 100 ms
400 Hz (100Hz) 60 ms
To guarantee accuracy over time, it is recommended to enable the runtime calibration. However, in some applications an
interruption of I/O is not permitted. In these cases, the runtime calibration parameter can be disabled, but at the expense of
module accuracy over time. By default the runtime calibration parameter is enabled.
Short-circuit to M or L
The module does not suffer any damage if you short-circuit an input channel to M or L. The channel continues to output valid
data and does not report a diagnostics event.
Special features of channels with respect to hardware interrupts upon limit violation
You can set the high and low limits triggering hardware interrupts separately for each channel in STEP 7.
Process interrupt
The table below shows the contents of the 4 bytes of additional OB40 information during process interrupts.
Content of the 4 bytes with additional information 2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
Byte
2 bits per channel to identify the range
High limit exceeded at channel 5 4 3 2 1 0 0
Low limit exceeded at channel 5 4 3 2 1 0 1
Free byte 2
Special
analog flags
Free byte 3
To Next Page
Loading...