Nanometrics RM-4, User Manual

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Setting Up the GPS Antenna
An RM-4 with GPS is shipped with an active antenna and a 10m cable.
Antenna position
The position of the antenna is critical to the operation of the GPS. Ideally, the antenna should be
placed in an electrically quiet location with a clear view to the horizon in all directions. The GPS
engine tracks the satellites from the horizon to overhead and down to the horizon again. The
antenna should be elevated above obstructions such as buildings, power lines, metal structures,
trees, etc. The GPS engine can “see” through foliage but the signal is scattered and attenuated.
The antenna should be oriented level.
Calculating the Power Consumption of the RM-4
The RM-4 supplies power to both the basic RM-4 and the GPS. Since the GPS alone consumes
almost as much power as the rest of a standard RM-4, it is important to take advantage of GPS duty
cycling at sites having restrictions on power consumption. As the RM-4 timeserver does not use
the duty cycling feature, do not enable duty cycling when using the time server.
The table below summarizes the power typically consumed by each component of the RM-4:
Basic RM-4 1.15 W
GPS Engine 1.1 W
The average power consumption of an RM-4 is approximated by the following formula:
P
=
1.15 W
+
1.1 W
%
GP S On-t ime
GP S Dut y-Cycle P eriod
For example, an RM-4 with GPS which has duty-cycling disabled typically consumes 2.25 W. If
GPS duty cycling is enabled, with a maximum on-time of five minutes and a period of 30 minutes,
the average power consumption will be less than 1.3 W.
Selecting a Power Source
The RM-4 can be powered from a number of different sources. The type of power source used will
depend mainly on the location of the instrument and the duration of the experiment. Remote
locations will require batteries and, possibly, solar panels. Mains power should be used where
available.
External 5V Power Supply
The standard RM-4 is supplied with an external 5V power supply. The power supply incorporates
continuous universal input, allowing it to operate from a wide range of AC line voltages without
the need to change wires or straps. The supply has an IEC 320 input voltage receptacle which can
be used worldwide. The detailed specifications for the supply are given in Appendix A.
Use only the power supply shipped with a standard RM-4 to connect to mains power . Although
over-voltage and reverse voltage protection is provided within the RM-4, there is still a risk of
damaging the unit if, for example, 12V is applied to the +5V pin of the power connector.
The power supply is not designed for outdoors use. Therefore, if operating the RM-4 outdoors, it
should be protected from the elements.
RM-4 Manual 15
4 - User Guide