Nortek Multi Parameter Probe

The Nortek Multi Parameter Probe is a stand alone water-quality data collection system for use in harsh environments. Basically it is a combination of field-proven sensors packaged in a robust delrin and brass frame. Data collection and control is handled by a standard Campbell Scientific CR-800 datalogger, packaged in a sturdy PE-plastic pressure housing. This provides a proven stable platform for data collection and retrieval and allows for easy customisation. Data is logged internally or may be output in a NMEA compatible format over RS-232. Data can also be read from the instrument using the SDI-12 or Modbus protocols. When a GPRS modem is connected all data is automatically sent to an FTP server.

Supported sensors:
- CS547 Conductivity / Temperature
- OBS-3+ Optical Backscatter
- CS525 ISFET pH probe
- InsiteIG Dissolved Oxygen/Temperature
- Valeport miniCT (replaces the CS547)
- Ponsel OPTOD-Dissoved Oxygen Sensor
- Chelsea Instruments TriLux - Blue-algea, Chlorophyll, Turbidity
- Ponsel C4E - Conductivity / Temperature

Internal sensors:
- Pressure (optional)
- Internal temperature
Derived parameters:
- Salinity
- Dissolved oxygen in mg/l

Monday, 15 February 2010

The Basic Idea

Making a probe like this is not exactly revolutionary. Our goal is to build a robust unit, both physical and software wise. Experience has shown that developing a reliable datalogger from scratch is a process that can take months, if not years ('Good software takes 10 years. Get used to it') So we soon decided to cut short and use a Campbell datalogger as the core of the system. Campbell already gone through the ten year cycle and datalogging is their core business so these units are extremely reliable. Interfacing to sensors is very well documented and programming is relatively simple.

The only disadvantage is their size. The brick shaped wall mount housing is not very well suited for mounting in a tube. So we take it apart...
And then it's not too bad. The metal box is the actual logger and the PCB just contains the connectors, fuses and overvoltage protectors. These parts will fit in a 10 cm inner diameter tube which is a very acceptable size.
Obviously we benefit most from choosing a Campbell datalogger if we also use their sensors. Unfortunately not all of these are really suitable for use in extreme sea-conditions but they will do fine in fresh to brackish water of rivers harbours and estuaries. This settles our choice for the Conductivity, Temperature, pH and OBS sensors. Choosing a Dissolved Oxygen sensor is easy. We will use the InsiteIG optical DO sensor which has already proven itself in the Nortek Oxybox. Finally we will need a pressure sensor. The easiest solution is to use the same sensor as used in the all other Nortek current meters.This will require some additional electronics for the signal conditioning but we will need an additional PCB anyway for connections, power supply and some interfacing.

Sunday, 10 January 2010

Nortek Multi Parameter Probe

When choosing a system for environmental monitoring at sea it is tempting to use the multi-function, lightweight multi parameter probes as commonly used in fresh water monitoring. Typical sensor suites like this are made by YSI, HydroLab or Eureka. When used in harsh environments however these instruments have shown to be just to fragile. Nortek therefore decided to try and develop a sensor suite that is more robust and able to withstand the harsh conditions at sea.
Requirements:
- Robust construction, able to withstand reasonable impact
- Low power
- Field replaceable sensors
- All sea water resistant materials
- Flexible communication options (RS-232, RS-485, MODBUS, SDI-12)