User Manual

Global Water Instrumentation
9
Real-Time Time Stamp
In cases wher e the time stamp is more critical, a real-time time stamp feat ur e c an be
enabled. T his is a f ac tory programmable feature that allows t he field station to
transmit the actual tim e the dat a r eadings wer e taken along with the sensor data.
Because the time stamp is transmitt ed through the sat ellite network, the amount of
data being sent increases, along with the subscription f ees c har ged by Orbcomm.
Depending on the transmission interval and the number of enabled sensor channels,
this feature can noticeably incr eas e these fees.
Power Consumption
The SIT65 dr aws different amounts of power depending on what mode it is in.
Typically, the controller draws 5m A all the time. When the radio is turned on, an
additional 75mA is used in standby and 2 amps are used for brief per iods when
transmitting. The analog sensor current, including 4-20m A output currents, is drawn
during the sensor war m-up time when readings ar e being taken. Active digital
sensors generally ar e powered up all the tim e and dr aw some current. Additional
current is dr awn when control outputs ar e pow er ing ex ternal devices fr om the SIT65
power supply. Other sources my als o apply . All these together for m an aver age
current that must be handled by the power supply if the system is to operate r eliably .
The cont r oller us es a v ariable power m anagement sc hem e 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 c ons umption from 80mA to 5mA. However, the SIT 65 can also be
remotely interrogated by c om m ands r elay ed through the satellite network. In order
for the request to be received, the modem must be turned on. T he modem m us t
also be turned on if c ommands ar e s ent to turn the control outputs on and off .
Two methods c an be used f or enabling remote interrogation of the SIT65 and
controlling t he outputs. One met hod is to leave the modem powered on all t he time.
This is a f actor y pr ogr ammable s etting only and is not recommended. The sec ond
method is to c ommunic ate with the stat ion at times when it is most lik ely to hav e
enough available power to k eep the modem turned on. With AC power, it is likely
that t he m odem w ill be powered up all of the time. Wit h s olar power ed systems,
suffic ient voltage to keep the modem turned on may only be available during daylight