FAQ bbe FluoroProbe

So, indeed the samples you are reporting about cannot be measured directly by the FluoroProbe. Your idea of diluting the sample in a defined way is a good one. There is no published guideline on how to do this, but please let me give you some thoughts:

 

• find a proper medium for dilution. consider the following rules
  • Generally, it is optimal to use a filtrated sample. For filtration a mesh size of 0.2 µm is recommended in order to be sure, no algae cells remain in the filtered matter. (To use filtrated sample has the additional advantage that you don't have to care about the influence of different amounts of yellow substances.)
  • If your sample comes from fresh water, you can replace the filtered matter (second best) by clean tap water, which you store for about one day after tapping and make sure that the temperature is as much as possible the same as of your sample when you mix it with the sample.
  • If your sample is a marine one, you cannot use the tap water. Then you have to use the filtrated sample. That's because the medium for dilution should have comparable composition of salts so that the Algae are not harmed.
  • Deionised water is generally not suitable.
• Find a dilution-proportion so that the FluoroProbe shows results below 500 µg Chl-a/l. Then you can calculate the original concentration of the sample.
• The transmission should be above 50% after dilution.

You can demonstrate the bbe++ software by using the built-in demo mode. This feature is described in the latest FluoroProbe manual on page 76:
To switch the bbe++ software to Demo Mode, select FluoroProbe under Tools → Settings → Access and disconnect all instruments. Then, select “DEMO Mode” from the device submenu. The software can then be operated as if a FluoroProbe were connected. Please note that some functions, such as calibration procedures, are limited in Demo Mode. To exit Demo Mode, simply restart the bbe++ software. Once Demo Mode is activated, the submenu will display the FluoroProbe-related options.

Important: The software must be in Online Mode before you can activate Demo Mode. Also, please make sure that the database is open. The Demo Mode option can be found under Device, not under Settings.

- excitation wavelengths: 365nm, 470nm, 525nm, 570nm, 590nm, 610nm, 700nm (Transmission)
- emission window: 685 - 700 nm
- color and intensity of actinic light: no actinic light

Yes, it has pressure sensor. It is located bottom of the probe. The current pressure sensor has a measurement range of 0–20 bar, which corresponds to a diving depth of approximately 200 m. The pressure sensor can withstand pressures corresponding to depths of up to 300 m (1.5 × full scale).

Depth measurement accuracy is approximately ±10 cm

This refers to the accuracy of the depth measurement itself. However, an offset between the depth measurement and the actual algae measurement needs to be taken into account. The pressure sensor is positioned at the very bottom of the probe, while the optical sensor used for algae measurement is located approximately 13 cm higher.

The FluoroProbe (FP) must be submerged at least 3/4 of its length (approximately 35 cm) to provide reliable measurements. This is necessary to avoid interference caused by stray light.

The wiper will be supplied by 6 pcs. AA batteries.
When the cleaning interval is every 2 hours the capacity of the battery pack is sufficient for 4 months.
So with some security it is needed to exchange the batteries every 3 months. The intervals are adjustable. Below is a table referring to battery life under different circumstances:

* assumes new Energizer AA batteries using a standard Hydro-Wiper.

 

 

The Limit of Detection (LOD) is calculated as the mean blank value plus 3 standard deviations of the blank. This corresponds to a detection limit of approximately 17 ng Chlorophyll-a/L.

 The Limit of Quantification (LOQ) is calculated as the mean blank value plus 9 standard deviations of the blank. This corresponds to a quantification limit of approximately 50 ng Chlorophyll-a/L.

The following specifications apply under ideal measurement conditions, i.e. measurements performed at a defined depth and with a defined amount of algae.

This is more difficult to define because determining the “true” chlorophyll concentration depends on the reference measurement method used. Therefore, the following values have been determined specifically for the FluoroProbe:

• Limit of Detection (LOD): 17 ng Chlorophyll-a/L
• Limit of Quantification (LOQ): 50 ng Chlorophyll-a/L
• Precision: approximately ±10%

These values were determined using stable algae cultures under controlled conditions. For natural water samples, an estimated measurement accuracy of approximately ±0.1 µg Chl-a/L can be assumed.

Yes, the FluoroProbe can provide measurement data directly online, and the same applies to the PhycoProbe (PP). This functionality can be configured in the device parameters. When Autostart is enabled, it is only necessary to monitor the RS485 communication line. The measurement results can then be extracted from the data stream or read directly. Whether a protocol converter is required depends on the receiving system. If the customer uses a data logger that supports RS485 and is able to extract numerical values from text strings, no protocol converter is required. However, if they require an SDI-12 interface, a protocol converter will be necessary.

The recommended supply voltage for the FluoroProbe (FP), which in most cases corresponds to the output voltage of the power supply, is 24 V DC. There are some Special Cases like the Online FluoroProbe that can also operate at voltages significantly below 24 V. However, it must be ensured that there are no voltage drops at the FP input that cause the supply voltage to fall below 10 V. At voltages below 10 V, RS485 communication may be disrupted.

When using a 12 V power supply, the voltage can quickly drop below 10 V due to cable resistance, depending on the cable length, as well as contact resistance at connectors and other connections. Therefore, 24 V remains the recommended supply voltage. If a 12 V power supply is already available, it can be easily and cost-effectively stepped up to 24 V using a DC-DC converter. Operation at 12 V or similar voltages is possible, but requires an individual assessment of the pull-up resistors and the cable lengths being used. For the Battery-Powered FluoroProbe (Standard Version) please note below items:

• If the device is supplied with only 12 V, it will operate, but the battery will not be charged.
• Over an extended period, the battery may become deeply discharged due to self-discharge. This can effectively result in battery failure.
• RS485 communication may also be affected if the battery becomes deeply discharged and the supply voltage is too low. In this case, the same considerations as described for the Online FluoroProbe apply.
• Therefore, it is also recommended to operate the battery-powered device with a 24 V supply, both for charging the battery and for continuous operation.
• A 12 V supply should only be used in individually agreed cases. There is a significant risk of damaging the battery, which could result in additional replacement costs.

When using Interval Measurement with a battery-powered device, it is essential to use an Autostart plug to operate the device. If an RS485 accessory is connected, such as a DPA or an RS485 cable with a Binder connector, a significant amount of current is drawn from the battery by the failsafe circuit (resistor network) of the RS485 interface. Depending on the accessory, this resistor network is located either in the cable (older Binder accessories) or on the DPA circuit board.

Connected accessories, such as the DPA, are also powered through the battery voltage that is made available externally via the SubConn connector. As a result, the battery current consumption can exceed 20 mA. When the Autostart plug is used instead, the power consumption is minimized. The device then requires less than 0.5 mA, allowing Interval Measurement to operate for several weeks on a single battery charge.

In practice, it is also unlikely that a customer would use Interval Measurement with a DPA permanently connected, since the DPA cannot remain connected while the device is being submerged.

When fully charged, the internal NiMH battery provides approximately 10 hours of operation under default settings, or around 800–1,000 measurements, depending on measurement duration and ambient temperature.

A typical measurement takes approximately 1 minute when the “power down after measurement” option is enabled. This feature significantly extends the operating time by switching the FluoroProbe off after each measurement. The Probe can be woken up again by sending another command. When switched off, the Probe consumes no power.

The FluoroProbe can also be operated continuously with the internal battery while an external power supply is connected. For the battery to be fully charged and maintained at full charge during continuous operation, the external supply voltage should be approximately 18 V or higher.

As the Probe uses NiMH batteries, some capacity may be lost over extended periods due to natural self-discharge.

The FluoroProbe communicates via RS485. It does not support Modbus. Using a Protocol Converter, communication via SDI-12 is also possible.

The color of the FluoroProbe’s lid LED (status LED) is determined by the battery charge level:

• > 50% battery charge: LED = green
• 24% to 50% battery charge: LED = orange
• < 24% battery charge: LED = red

The 10.5 V value corresponds to the software shutdown threshold.

The recommended flow rates are approximately:

• Maximum flow rate: 1.8 L/min
• Minimum flow rate: approximately 0.18 L/min (estimated at 1/10 of the maximum flow rate)

The flow-through attachment has an open chamber volume of approximately 160 mL. The minimum flow rate is an estimate based on the chamber volume and the required water exchange rate.

Note: The minimum flow rate has not been experimentally determined and should therefore be considered an estimate.

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For sure the AlgaeLabAnalyser (ALA) is the better choice for laboratory analysis. It provides the best results due to its separate measuring chamber with an integrated stirrer, which ensures well-defined and reproducible measurement conditions.

With the optional Genty measurement using variable fluorescence, the ALA can also determine photosynthetic activity.

The FluoroProbe (FP) can also be used for laboratory chlorophyll analysis when combined with the Workstation and cuvette. However, this is an additional application of the FP rather than its primary purpose. The FluoroProbe is primarily designed for field operation, especially for profiling measurements and long-term underwater measurements. Therefore, if the main application is laboratory analysis only, the AlgaeLabAnalyser is the recommended instrument.

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Yes. The FluoroProbe can measure continuously while being submerged. It does not need to be stopped or adjusted at a fixed depth before taking a measurement. For depth profiling, the FluoroProbe is lowered continuously through the water column while recording the algae concentration at different depths. The fastest measurement interval is approximately one measurement per second. Therefore, a recommended submersion speed is approximately 1 m every 3 seconds.

The FluoroProbe can be used in two main ways:

• Depth profiling: An operator lowers the FluoroProbe through the water column and records the algae concentration as a function of depth.
• Fixed-depth monitoring: The FluoroProbe can be fixed at a defined depth, for example from a research boat, and continuously monitor the algae concentration at that depth over an extended period.

In fixed-depth operation, the FluoroProbe continuously measures the algae concentration in the surrounding water but does not provide a depth profile. The standard FluoroProbe does not include an automatic mechanism for moving the probe to predefined depths at specific times.

In summary, the FluoroProbe can either be lowered through the water to obtain a depth profile or fixed at a specific depth for continuous long-term monitoring.

To obtain reliable measurement results, follow these recommendations:

1. Start the measurement before submerging the Probe.
   After starting the measurement, wait until the first data appear on the screen. You can then place the Probe into the water.
2. Remove air bubbles from the optical system.
   Once the Probe is submerged down to the cable connection, quickly move it to the left and right. This helps prevent air bubbles from remaining on the optical components and affecting the measurement.
3. Maintain a steady submersion speed.
   Lower the Probe at a speed of approximately 30 cm per second.
4. Perform a control measurement while returning to the surface.
   Once you reach the seabed, stop the measurement and save the data. As a control, perform a second measurement while bringing the Probe back up to the surface. Comparing the two measurements can help identify measurement noise and improve the reliability of the results.