Xylem SIT65 SATELLITE INTERNET TELEMETRY - Manual (Page 9)

Global Water Instrumentation
9
Real-Time Time Stamp
In cases where the time stamp is more critical, a real-time time stamp feature can be
enabled. This is a factory programmable feature that allows the field station to
transmit the actual time the data readings were taken along with the sensor data.
Because the time stamp is transmitted through the satellite network, the amount of
data being sent increases, along with the subscription fees charged by Orbcomm.
Depending on the transmission interval and the number of enabled sensor channels,
this feature can noticeably increase these fees.
Power Consumption
The SIT65 draws different amounts of power depending on what mode it is in.
Typically, the controller draws 5mA all the time. When the radio is turned on, an
additional 75mA is used in standby and 2 amps are used for brief periods when
transmitting. The analog sensor current, including 4-20mA output currents, is drawn
during the sensor warm-up time when readings are being taken. Active digital
sensors generally are powered up all the time and draw some current. Additional
current is drawn when control outputs are powering external devices from the SIT65
power supply. Other sources my also apply. All these together form an average
current that must be handled by the power supply if the system is to operate reliably.
The controller uses a variable power management scheme that provides a balance
between current draw and available features. This process relies on the fact that the
controller has the ability to switch the modem off when not transmitting, reducing
standby power consumption from 80mA to 5mA. However, the SIT65 can also be
remotely interrogated by commands relayed through the satellite network. In order
for the request to be received, the modem must be turned on. The modem must
also be turned on if commands are sent to turn the control outputs on and off.
Two methods can be used for enabling remote interrogation of the SIT65 and
controlling the outputs. One method is to leave the modem powered on all the time.
This is a factory programmable setting only and is not recommended. The second
method is to communicate with the station at times when it is most likely to have
enough available power to keep the modem turned on. With AC power, it is likely
that the modem will be powered up all of the time. With solar powered systems,
sufficient voltage to keep the modem turned on may only be available during daylight