Operating Instructions

Siemens Industry, inc. 52
Pulse Inputs – MD-12HD/MD-24HD/MD-48HD Only
MD-12HD meters are equipped with 4 pulse inputs and MD-24HD/MD-48HD meters 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 50 mS 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 Output
Beginning in June, 2020 the hardware alarm circuit in all MD-xxHD meters is transitioning from
electromechanical (SPDT) relays to an isolated open collector type (shown below). This transition has
been made to focus on improving the behavior of the Voltage Phase Loss alarm response.
The alarm is designed to be connected to an external DC source between 5 and 24 volts and used with a
customer supplied pullup resistor. A 10K-ohm 1/4 watt resistor is the recommended load for this circuit.
For more information regarding setting up alarms see the Configuring Alarms section earlier in this
manual.
See the register list, ViewPoint HD, or instructional videos for more information.
Note: The Master Alarm relay is intended for low voltage DC connections.
>50 mec
>50 mec