Operating Instructions

53 Siemens Industry, Inc.
12 Volt Auxiliary Power
The MD-12HD, MD-24HD, and MD-48HD meters provide an auxiliary 12-volt output (200 mA max.) that is
derived from an auxiliary winding on the MD-xxHD’s line-connected power supply. The 12-volt supply
voltage is unregulated but protected by a self-resetting fuse. The purpose of the supply is to power external
radio equipment or provide supply voltage for analog sensors, such as 4 to 20 mA current loop devices. If
full-rated current is drawn from this terminal, the minimum operating voltage of the L1-L2 power supply is
100 Vac.
This option is unavailable on the MD-3HD.
Access Restriction Limitations
If security levels have been set up in the meter, no data is accessible through the LCD user interface or
MD-xxHD Web App without entering the PIN credentials. Note, however, that protocols such as Modbus
do NOT SUPPORT ANY LEVEL OF security such that any network traffic acting as a master can retrieve
and write data from the registers. Generally, this will require knowledge of the IP address or slave ID and
the register list which discourages casual intrusion.
Security PIN Protection
MD-xxHD meters have two levels of PIN protection that users can choose to assign for restricting access
to meter information. The PIN logic is described in the figure below. The default user entry (on power up
or time-out) is 0000 which satisfies both the Read Only and the Read/Write default register settings.