Siemens LMV5 Quick Start Manual page 190

After viewing Figures 7-2.1 and 7-2.2, the keen observer most likely notices some numbers
that do not make immediate sense.
Specifically, these numbers are the milliamp signal used for standardization, the 60 Hz VFD
output frequency corresponding to 19.5 mA input, and a signal greater than 20 mA.
The next couple of paragraphs will explain why these and other numbers associated with
the VSD have the values that are shown.
When standardized, the LMV52 VSD control only outputs 19.5 mA to the VFD and the
resulting motor RPM (read by the speed wheel) is recorded for the standardization.
The reason 19.5 mA is output for the standardization instead of 20mA is so that there is
additional room to increase the signal to the VFD if the motor RPM drops due to increased
motor load.
For similar reasons, the VFD should be spanned so that:
4mA input signal = 0 Hz and a
20mA input signal = 62.5 or 63 Hz.
This means that at a 19.5 mA signal to the VFD, the frequency output of the VFD should be
about 60 Hz.
This is all done in an effort to have some reserve built into the control system so that the
blower can make rated speed under all environmental conditions.
The VSD control appears as another actuator when commissioning the fuel air ratio curves.
The only main difference is that the:
SQM4 actuator are in degrees and have a range of 0 to 90 degrees, while the
VSD control is in percent and has a range of 10 to 100 percent.
When a particular percentage of VSD is saved for a point, the RPM corresponding to that
percentage is maintained by varying the milliamp signal to the VFD.
The limits of this control range are shown in Figure 7-2.1.
On the top end, the LMV52 VSD control will output up to almost 22 mA if the blower RPM is
low at 100% load.
However, this typically does not happen if the VFD is spanned as described above.
If the upper control range limit is reached and the blower RPM is still low, a message will be
displayed on the AZL that states "Fan speed not reached".
If the lower control range limit is reached and the blower RPM is still high, a message will be
displayed on the AZL that states "Control range limitation VSD Module".
Fan speed not reached results in an immediate lockout,
and Control range limitation VSD Module will result in a lockout if the blower RPM does not
come into range in about 5 seconds after the warning is displayed.
LMV5 QSG Rev 4 Sec 7 Pg 6 www.scccombustion.com