FSI Frequently Asked Questions

Frequently Asked Questions (FAQs)

CTDs
How large is the external field of the conductivity cell on my CTD? How does this affect the mounting?
The external field of FSI ceramic conductivity cells is a 10-cm-diameter sphere from the center bore of the cell. This means that the cell should have a free radius around the conductivity cell of 10 cm minimum. Objects within this radius must be electrically stable, either a complete dielectric or a conductor, and their position must be fixed in relation to the sensor. For more information, read Application Note on Ceramic Inductive Conductivity Sensor Proximity Effects.


FSI Ceramic Cell	FSI NXIC Cell

FSI's NXIC-cell based conductivity sensors do not have an external field, so proximity effects do not need to be considered in mounting the units.

How does bio-fouling affect operation of my conductivity sensor, and how can I minimize the effect?
Build-up of biological growth on the conductivity sensor changes the geometry of the conductivity cell and decreases the sample volume, which affects the conductivity calibration.

Ceramic conductivity cells can be painted with TBT anti-fouling paint. Because the paint also changes the geometry of the conductivity cell, the sensor should be calibrated with the paint already applied. Cell geometry will change slightly as the paint abrades.

NXIC CTD units can be supplied in a special anti-fouling mechanical apparatus (BIO versions) for moored applications in sites with significant bio-fouling. The NXIC cell is mounted between tubes with copper screens attached to each end. This design has been effective in slowing bio-fouling of the NXIC sensor.

Both types of inductive conductivity cells can be cleaned without affecting sensor calibration. See FAQ on Conductivity Sensor Cleaning.

How can I clean my conductivity sensor, and will it affect the calibration?
Inductive conductivity cells can be cleaned without affecting calibration. Use a soft brush to clean inside and outside surfaces of the cell. The NXIC conductivity cell is very robust, but ceramic cells require careful handling to avoid breaking the cell.

My NXIC-CTD-ADC is being deployed with external sensors attached. How can I tell how much current is being drawn by the whole system and how do I determine what my battery life will be?
Battery Life Estimator
Activate the Battery Life Estimator, which is also included in the CTDPro software supplied with NXIC units. In the Battery Life Estimator, select the operating parameters (i.e., interval time, on-time, delay before deployment). You will also need to enter the total current used by the NXIC CTD and any sensors that you will be using.

Typical current draw of the NXIC-CTD unit when run using the internal battery pack is:
NXIC-CTD-ADC or NXIC-CTD-BIO-ADC: 130 mA. Contact FSI to discuss external sensors.

The actual current drawn by the NXIC CTD and all external sensors is tested by FSI and included in the customer configuration document supplied with NXIC units.

FSI recommends that you start with fresh batteries for every deployment. For deployments longer than a few days using 3 or 4 external sensors, we recommend powering the system from an external power source. For deployments where the delay time is over a month, we recommend that the battery be disconnected until closer to the deployment date. NXIC units draw approximately 5 mA in delay mode, which will drain about 1/10 of the battery over a month. Do not leave batteries connected while the unit is in storage.

How often does my NXIC CT/CTD unit need to be recalibrated? Do I need to send it to the factory for recalibration?
There is no set schedule for recalibration of a NXIC CT-CTD unit - much depends on the amount of bio-fouling in the environment in which the unit has been deployed and the required accuracy for your project. Bio-fouling can be cleaned from the sensor without affecting calibration of the unit - see How to Clean the NXIC Conductivity Sensor.

Request an RMA for recalibration.

How is the temperature response-matched to conductivity in the NXIC sensor?
When temperature and conductivity are needed to calculate salinity, different response times of the sensors can cause errors in the salinity calculation. Temperature sensors typically have a slower response time than conductivity sensors. In addition, because of the geometry of the NXIC conductivity cell, the temperature sensor is installed at the outlet of the conductivity cell, providing an additional lag.

FSI sensors have been tested in a double-diffusive interface tank at the Woods Hole Oceanographic Institute to determine the appropriate lag factors to be applied, so that conductivity and temperature are properly matched for calculating salinity. Corrector factors are set out in the attached Lag Corrector for the NXIC Conductivity Cell.

I'm having difficulty downloading data from my NXIC via RS-232 on a laptop operating off battery power.
Due to the way Windows XP works, sometimes the RS-232 port corrupts data files downloaded when operating off battery power. Downloading via the laptop's USB port using an RS-232 to USB converter typically works better.

When running the diagnostic tests in CTDPro, two error windows came up (Pressure A/D Readings and Temperature noise are too high). These errors appeared after the deployment. Why are these errors being shown? How can they solve these? An additional error message popped up when the conductivity test was made. Are these errors software-related?
There are two likely reasons that these errors appear. In early versions of CTDPro, if diagnostics were done in an unstable environment, such as while the unit was wet or the temperature was changing quickly, the software might not work correctly. This was corrected in the latest version of CTDPro and the latest firmware version of NXIC units.

Download the current version of CTDPro

Download the current firmware version.

How can I make sure that the NXIC-CTD is in low-power mode while it is not deployed?
CTDPro software has an LP button in the toolbar. Click this button, or type LPWR in terminal mode, while communicating with the NXIC unit.

Also, read more about External Switch capability with NXIC-CT and CTD units.

My 3" MCTD has a switch that allows me to put it into Sleep mode between deployments. Is this available with the NXIC-CTD?
Yes, an external switch option is now available for NXIC-CTD units. Existing NXIC units can be upgraded with the switch, or it can be ordered with new units. For information, contact fsi@falmouth.com.

Installing a NXIC CTD Endcap Switch Kit
Using the NXIC CTD Endcap Switch
Using the NXIC CTD Autolog Feature

I want to add a Turbidity/Fluorometer/Oxygen sensor to my CTD. Can this option be retrofitted?
MCTD2", MCTD3", NXIC-CT-ADC-BIO, NXIC-CTD-ADC and NXIC-CTD-ADC-BIO units have several A/D inputs which accept signals from external sensors with 0-5V output. Integration of these sensors can typically be accomplished by adding a connector and internal wiring changes. For more information contact fsi@falmouth.com.

Current/Wave Meter
How deep can I deploy my FSI Wave Meter?
FSI Wave Meters use the PUV method of measurement, meaning that wave height and direction are calculated from pressure and horizontal velocity measurements. The depth of deployment is related to the period of the waves being measured. Following is a chart showing the minimum wave period that can be accurately measured at the corresponding depth.

Deployment Depth (M) Min. Wave Period (Sec.)

20 4.4

18 4.2

16 4.0

14 3.7

12 3.4

10 2.8

6 2.4

4 1.9

2 1.1

See the application note on Wave Post Processing for more information on how the FSI 3D Wave meter measures wave direction and height. Other considerations in mounting the wave meter are:

The maximum depth correction possible with an RPT-based (Resonant Silicon Pressure Transducer) wave meter is 31.63 meters; the 3D-WAVE meter will not provide accurate directional wave data if installed below this depth.

How can I determine the expected battery/memory life of my current meter?
FSI supplies a BatLife software program that calculates these parameters for a given configuration. You may download this from our FTP site at: ftp://ftp.falmouth.com/Software/BatLife/

If my 2D-ACM data provides a current direction of 180.121 and speed of 10.034, what exactly does this mean?
Current direction (unlike wind) is measured in the direction to which it is flowing. In this case, the current is 10 cm/sec, and it is flowing to the South.

Does my current meter require calibration? If so, how often?
The initial current meter calibration comprises three aspects - tilt, compass, and velocity. FSI recommends that all three parameters be recalibrated after one year of use.

I want to add a Turbidity/Fluorometer/Oxygen sensor to my current meter. Can this option be retrofitted?
2D-ACM and 3D-ACM current meters include A/D inputs which accept signals from external sensors with 0-5V output. Integration of these sensors can typically be accomplished by adding a connector and internal wiring changes. For more information contact fsi@falmouth.com.

Updated 5/2/07