45 Siemens Industry, Inc.
Pulse Inputs
MD-12HD meters are equipped with 4 pulse inputs and MD-48HD meters (hardware version I) are
equipped with two pulse inputs. Pulse counting supports accumulation of consumption data from any
external meter using a dry contact (Form A Relay) or open collector outputs. The MD-xxHD pulse inputs
are compatible with “low speed” meters. The pulse duration must exceed 50mS in both the logic low and
high state allowing for a maximum input frequency of 10 Hz.
Pulse scaling, resetting and accumulated values are accessed through registers and are “system” in
scope. See the register list, ViewPoint HD, or videos for more information.
ALARM (SPDT)
The MD-xxHD meter supports user-configurable alarms for over-current, under-current, over-voltage, and
under-voltage. ViewPoint HD helps users set these values by allowing for values to be entered using
direct entry mode or specifying the limits as a percentage of nominal.
Alarm persistence settings are used to allow for temporary conditions, such as a motor starting, that are
beyond trigger limits. For example, in the case of meter upset from ESD events, short persistence
settings may lead to false alarm triggers. When any alarm condition has been satisfied throughout the
persistence interval, the MD-xxHD trips the MASTER ALARM relay, which is an electromechanical relay
on the PCB.
Once tripped, the relay can only be reset by clearing the alarm through Modbus register/BACnet object
2451”
The Master Alarm relay can be hard wired to an interrupt or polling circuit in a host system allowing for a
more rapid response than the data polling frequency, if desired. The status of each alarm is determined
by reading status registers. See the register list, ViewPoint HD, or instructional videos for more
information.
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