User`s manual

Manual revision 016 Section 4: Deploying and Operating FastCAT SBE 49
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Autonomous Sampling
The FastCAT runs continuously, sampling data at 16 scans per second (16 Hz)
and transmitting the data real-time. The FastCAT can be set to average up to
255 samples, transmitting only the averaged data. AutoRun defines how
autonomous sampling starts and stops:
If
To Start Sampling
To Stop Sampling
AutoRun=Y
Turn on power.
• Turn off power, or
• Send Stop, click Stop on
Seaterm’s Toolbar, or type Ctrl Z.
(Stopping this way allows you to
then send commands to check or
modify the setup.)
AutoRun=N
Send Start.
After the conductivity cell enters the water there is a user-programmable delay
before pump turn-on so that all the air in the pump tubing can escape. If the
pump motor turns on when there is air in the impeller housing, priming is
uncertain and a proper flow rate cannot be ensured. The cell inlet and pump
outlet must not come above the water surface or the prime will be lost.
• If prime is lost, stop sampling. Wait at least 5 seconds, then submerge the
FastCAT completely, restart sampling, and wait for the pump delay time
before beginning the profile.
Pump turn-on occurs when two user-programmable conditions have
been met:
• Raw conductivity frequency exceeds the minimum conductivity
frequency (MinCondFreq=)
Set the minimum conductivity frequency for pump turn-on above the
instrument’s zero conductivity raw frequency (shown on the FastCAT
Configuration Sheet in the manual), to prevent the pump from turning on
when the FastCAT is in air.
 For salt water and estuarine applications -
typical value = zero conductivity raw frequency + 500 Hz
 For fresh/nearly fresh water -
typical value = zero conductivity raw frequency + 5 Hz
If the minimum conductivity frequency is too close to the zero
conductivity raw frequency, the pump may turn on when the FastCAT is
in air as result of small drifts in the electronics. Some experimentation
may be required, and in some cases it may be necessary to rely only on the
pump turn-on delay time to control the pump. If so, set a minimum
conductivity frequency lower than the zero conductivity raw frequency.
• Pump turn-on delay time has elapsed (PumpDelay=)
Set the pump turn-on delay time to allow time for the pump to fill with
water after the FastCAT is submerged. Determine the turn-on delay by
immersing the FastCAT (power off, not sampling). Measure the time
needed to completely fill the pump exhaust tubing (by watching for when
air bubbles stop coming out of the exhaust); 20 seconds is typical. Set the
delay to approximately 1.5 times longer (30 seconds). When actually
using the FastCAT, be sure to soak the instrument just under the surface
for at least the time required for pump turn-on.
Pump turn-off occurs when the conductivity frequency falls below the
minimum conductivity frequency (MinCondFreq=).
Pump
exhaust
tubing