External Tests (Optional) - Siemens LMV37.4 Series Basic Documentation

Building Technologies
12.15.3

External tests (optional)

In addition to the LMV37.4 internal tests, various states may also be monitored by an
external PLC or control. Selected process parameters, e.g. the current phase, can be
read out via Modbus for this purpose. In this case, the LMV37.4 is shut down via a self-
locking NC contact of the PLC in the safety loop (X3-04 pin 1 and pin 2) or in series with
the load controller ON signal (X5-03 pin 1 and pin 4).
Impact of the trimming range restriction with PLC
The defined assignment between the current setting and trim impact (4...20 mA is
...
shown as -15 +25 %) must also be taken into account by the PLC. Particularly when
reducing the possible trim range (parameter 547 / 548 or 567 / 568), the PLC must also
take the reduced limit values into account. The relevant parameters can be read out via
Modbus for this purpose.
To guarantee that, despite tolerances between the PLC analog output and LMV37.4
analog input, the maximum limits for the trimming can be achieved, the PLC must
deliver a current value that is approx. 0.5% (i.e. approx. 0.2 mA) off the set limit values
(over for the upper limit, under for the lower limit).
No. Parameter
547 Lower range limit trim function
548 Upper range limit trim function
External supervision: Target/actual comparison of the trim specification
The single-channel version of the LMV37.4 analog value recording is not fail-safe. The
control unit responsible for the specification of the 4...20 mA signal for O2 trimming can
either trigger a safety shutdown or shutdown via an NC contact if an excessively large
deviation is detected between the trim setpoint and the determined trim specification of
the LMV37.4. To this end, the trim specification of the LMV37.4 can be read out via
Modbus (raw value, target value with limitation and damping, as well as the current
active trim influence).
SPS
Figure 88: Trim supervision with PLC
With this supervision, the PLC can create a closed loop over the analog input of the
LMV37.4 and the trim specification, including the analog output of the PLC, via Modbus.
External supervision of the residual oxygen content in the flue gas
Particularly for a trim specification based on an O2-measurement, there is the option of
additional supervision of the flue gas values with regard to the minimum / maximum O2
value. For this, the PLC can read out the LMV37.4 phase and LMV37.4 output via
Modbus and supervise output-dependent minimum / maximum O2 values. This ensures
that the application is always operated in the correct working range.
In the event of an error, a safety shutdown via the safety loop or a shutdown via the load
controller ON signal can be triggered as a response as required. Another option in the
event of an error is to deactivate the trim function via a 10 mA current setting in the PLC.
Basic documentation LMV37.4...
12 Fan control
4...20 mA trim signal
Modbus
LMV3...
7544z10en/0916
CC1P7546en
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