ISUS V3 Nitrate Sensor

ISUS V3

ISUS V3 nitrate sensor is a real time, chemical free sensor designed to overcome the traditional challenges associated with reagent-based nitrate analysis in aquatic environments.

How does the ISUS compensate for long term drift?

Because the ISUS is an active optical instrument with an internal UV light source and spectrometer, gradual changes in the baseline spectra can occur. To check for instrument drift, we recommend users check the baseline prior to deployments by sampling an aliquot of ultra pure de-ionized water (DIW). To do this, first clean the probe tip and warm up the instrument for 8-10 minutes. Then log 1 minute of data with the probe tip submersed in DIW, making sure that there are no bubbles present on the probe tip. If the nitrate reading for the DIW sample is >-2 or <+2 uM, the instrument has not drifted significantly. If the nitrate reading is outside this range, the instrument has drifted and should be corrected by updating the reference spectrum in the cal file. For V3 instruments, the ISUSCom software has a function to update the cal file. For V1 & V2 instruments, the ISUSCal program is required. After uploading the new cal file to the instrument, it is a good idea to run another DIW check to make sure the procedure has worked.

I am planning on doing a mooring deployment which requires relatively tightly spaced sampling. Are there any issues I need to consider when making a schedule file?

There are three main points to consider when making a new schedule:

  • Power: if you are using a battery to power the ISUS, make sure you have enough battery capacity to cover the schedule you intend to use. The ISUS draws about 7 watts of power with the lamp turned on
  • Memory: make sure the scheduled frequency and duration don't create more than 256 MB of data. The ASCII full frame is 1675 bytes
  • Lamp time: the UV lamp used in the ISUS has an effective lifetime of ~ 1000 hours. It is usually a good idea to conserve lamp hours by only collecting meaningful data

How is the ISUS V3 different from V2?

The most significant improvement with the V3 is the addition of full USB communications and data transfer ability. The V3 comes with the ISUSCom software, a new Windows-based program designed to make the instrument setup and file transfer processes easier. V3 users no longer need to use HyperTerminal and Y modem transfers to retrieve data. It can all be done now at high speed with one cable in a professional windows environment. 

The ISUSCom software also offers users the ability to update the instrument sampling schedule for mooring deployments, perform in field calibrations, view and log data. It effectively consolidates functions previously performed by HyperTerminal, ISUSCal, ISUSSchedule and SatView into a single, simplified program.

How does the ISUS compensate for long term drift?

Because the ISUS is an active optical instrument with an internal UV light source and spectrometer, gradual changes in the baseline spectra can occur. To check for instrument drift, we recommend users check the baseline prior to deployments by sampling an aliquot of ultra pure de-ionized water (DIW). To do this, first clean the probe tip and warm up the instrument for 8-10 minutes. Then log 1 minute of data with the probe tip submersed in DIW, making sure that there are no bubbles present on the probe tip. If the nitrate reading for the DIW sample is >-2 or <+2 uM, the instrument has not drifted significantly. If the nitrate reading is outside this range, the instrument has drifted and should be corrected by updating the reference spectrum in the cal file. For V3 instruments, the ISUSCom software has a function to update the cal file. For V1 & V2 instruments,  the ISUSCal program is required. After uploading the new cal file to the instrument, it is a good idea to run another DIW check to make sure the procedure has worked.

Should I provide my ISUS or SUNA with a warmup time before recording data?

We recommend updating the ISUS or SUNA's reference spectrum portion of the calibration with the instrument in the same state it will be used in the field. To update the reference spectrum, you will have to run the calibration feature in ISUSCom or SUNACom using a pure water sample.

For best results, we recommend the following:

1. For profiling situations, when the instrument will be run for extended times, the reference spectrum should be updated after the sensor has been run for several minutes. This will allow the Nitrate reading to stabilize.

2. For moored applications, we recommend that the instrument only be run for a short duration to collect the pure water data during the calibration. Data collection in the field should only have the instrument run for 20 seconds per acquisition.

What is the result of using the "Reprocess Nitrate Data" function under the ISUSCom Processing Menu ?

The "Reprocess Nitrate Data" tool in ISUSCom allows the user to select a calibration file and a raw file.
The resulting ASCII file contains a column for the original Nitrate concentration as calculated by the ISUS, using the calibration file onboard the sensor, and a column of recalculated Nitrate using the chosen calibration file.

My ISUS is running slower than normal. What is causing this?

An ISUS should run at approximately 1Hz. Check the amount of storage space left on the internal memory; old data files should be downloaded or deleted from the disk on a regular basis. Additionally, the Messages.log files should be periodically removed. Download and/or delete these files to restore normal operation.

Can an ISUS V2 be used with ISUSCom?

No. An ISUS V2 does not have the correct hardware to be used with ISUSCom. If you have an ISUS V2, and wish to use it with this software, please contact Satlantic Customer Support to discuss upgrading your ISUS.