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than the high limit and a low alarm when the reading is less than the low limit. Two additional methods of
processing alarms are available that are intended for analog inputs that have a negative or bipolar input signal.
• With the standard method of processing input signals and alarms, the sign of the input signal is the sign
of the reading. Alarms are processed with the most positive value being a 'High' reading and the most
negative value being a 'Low' reading. Also, the channel reading is compared to all alarm limits. So, in the
example at right and with a temperature of -4.0 °C, two low alarms would turn in: one for +5.0 limit and
one for the -3.0 limit. To process an analog channel's alarms using this method the channel's polarity
parameter is set to '+' and its alarm limit mode parameter is set to 'N' (for Normal).
• With the negative method of processing input signals and alarms, the processing is reversed from the
standard method. The sign of the input signal is inverted (* -1) to get the channel reading. Alarms are
processed with the most negative value being a 'High' reading and the most positive value being a 'Low'
reading. The channel reading is compared against all alarm limits to determine alarms. This is intended
for inputs whose signal is always negative, such as plant voltage.
This makes it possible for -56.0V to be a high limit (given a float voltage of -54.0V), when in previous
LMS1000 versions, it must be a low limit. To process an analog channel's alarms using this method the
channel's polarity parameter is set to '-' and its alarm limit mode parameter is set to 'N' (for Normal).
• With the bipolar method of processing alarms, a high or low alarm can only occur if the sign of the
channel reading is the same as the sign of the alarm limit that has been exceeded. This is useful for
detecting both high charge and discharge currents on a battery shunt. For example, assume a shunt is
wired for a negative float current reading, and it has a high alarm limit of –6.0 amps to detect a high float
current. It can then also have a high limit of +100.0 amps to detect a high discharge current. So, in this
example there are two high alarms, with opposite signs. To process an analog channel's alarms using
this method the channel's polarity parameter is set to '+' and its alarm limit mode parameter is set to 'B'
(for Bipolar).
Vertiv™
| NetSure™ LMS Data Processing Unit User Manual (Section 5847) | Rev. ZA
Temp
Limit 3 30.0 H
Limit 2 5.0 L
0
Limit 1 -3.0 L
In the default mode, it is
possible to have low alarms
0
Limit 2 -48.0 L
Limit 1 -54.0 H
With v6.3, the –48.0 limit
-Volts
can now be a low limit,
102
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