General overview
Acquiring samples
There are basically two fundamental ways to acquire samples: they can be acquired by polling or according to a defined sampling schedule.
A polled measurement is performed simply via the poll command. A sample acquired only for polling purposes is not stored in the logger's memory.
Scheduled samples are configured using various commands. Scheduled samples may be stored in the logger's memory, and they can also be streamed directly out of the logger in real-time; see the stream and storage parameters of the schedule command. Gen-4 instruments have the ability to sample with different measurement parameters according to different schedules, and for this, we need to understand the concepts of channels, groups, schedules and configurations. These will be described briefly in the sections below, but briefly:
Channels can be arranged in groups.
Each group may be associated with one or more schedules.
Each schedule can have its own sampling mode and parameters, independent of other schedules.
A sampling mode can be as simple as a single fixed sampling rate, or as complex as a multi-rate scheme driven by the logger's depth in the water.
One or more schedules are collected together into a configuration.
The logger is enabled using one of these configurations, and it will execute the associated schedule(s) to acquire data.
Gen-4 instruments are also designed to support retention of data in the memory from more than one deployment; it will no longer be necessary to delete the previous deployment's data before starting a new one.
A major feature of RBR instruments is that polled and scheduled samples can occur at the same time, they are not mutually exclusive.
The acquisition of data can be constrained or controlled in other ways, by configuring a gating condition such as time and twist activation. If available, these features apply to the entire instrument, not on a per-schedule basis.
Refer to the remaining Quick start sections for examples of different sequences of commands used to set up different ways to acquire samples.
Channels
Channels are the basic elements of what will become a set of data acquired by the instrument. As with previous generations of RBR instruments, Gen-4 products can measure a wide range of physical properties of the water, such as temperature, pressure, conductivity, turbidity, dissolved oxygen, chlorophyll, and so on. This list is not exhaustive and the number of sensors supported continues to increase regularly. For each one of these physical properties measured - for example pressure - the instrument has exactly one channel. Instrument channels may also be available for physical properties that are not measured directly, but that are derived by calculation from measured channels - for example salinity, which is derived from conductivity, temperature and pressure. In summary:
A channel represents a single parameter of interest recorded by the logger. The parameter may be directly measured or derived by calculation from other parameters.
Although channels themselves are not a new concept in RBR instruments, the way in which they are specified for sampling is new for Gen-4.
Users can not create or delete channels. Modification of channel details is limited to its calibration or other specialised parameters (for example gain, if applicable).
Channels are created and assigned a label at the factory when the logger is built.
Any channel can be a member of more than one group.
One configuration is selected when the logger is enabled; this specifies, via the list of schedules, which groups will be sampled. Any channel not belonging to at least one of these groups will not be sampled during the deployment.
When sending commands that access or modify information associated with a channel, the channel is referred to by its label - for example, temperature_00.
Associated command(s):
Groups
A group is a collection of one or more logger channels.
In the context of sampling, a group (or a list of groups) determines which channels will be sampled according to a given schedule.
Channels can not be directly assigned to a schedule; this can only be done through a group. A group may contain only one channel if necessary.
The logger can maintain a pool of groups, any of which can be included in the group list of one or more schedules.
The user has complete control over the creation, content, and deletion of groups.
When creating a group, the user assigns it a label; group labels must be unique.
One configuration is selected when the logger is enabled; any group that is not associated with a schedule included in that configuration will not be sampled as part of the deployment.
Associated command(s):
Schedules
A schedule determines how a given subset of groups will be sampled during the deployment.
Multiple schedules can be included in a configuration, enabling groups to be sampled in different ways.
The logger can maintain a pool of schedules, any of which can be included in one or more configurations.
The user has complete control over the creation, content, and deletion of schedules.
Each schedule contains a list of channel groups, one sampling mode, and a set of sampling parameters appropriate for the mode.
When creating a schedule, the user assigns it a label; schedule labels must be unique.
One configuration is selected when the logger is enabled; only the schedules included in that configuration will be executed during the deployment.
Associated command(s):
Configurations
A configuration is essentially a list of the sampling schedules to be executed by the logger when it is enabled.
The logger can maintain a pool of configurations; when the logger is enabled, the user specifies exactly one configuration that determines how the logger will behave during the deployment.
The user has complete control over the creation, content, and deletion of configurations; if necessary, the logger can always be restored to its as-shipped factory default configuration.
When creating a configuration, the user assigns it a label; configuration labels must be unique.
All elements of a configuration must be valid and consistent before it can be used to enable the logger.
The selected configuration forms a subset of the metadata for the deployment, and a copy is stored in memory when the logger is enabled.
Associated command(s):
Datasets
A dataset is the collection of all sample data and all supporting auxiliary data relating to a single deployment of the logger, stored in the logger's data memory.
It comprises a number of storage objects; for convenience, these storage objects can be thought of as "files", and will be referred to as such. However, they may not necessarily be implemented as actual files within the memory.
One file contains the deployment metadata; this is a snapshot of the logger's state and parameters at the time the deployment was enabled.
A second file contains all the events that occurred during the deployment. Essentially, an event is a record of anything that occurs during the deployment that is not sample data.
The remaining file(s) contain the sample data, one file for each schedule defined for the deployment.
The user creates a dataset by enabling the logger using the enable command, assigning it a label and associating it with a configuration.
Only one dataset can be active (reflected by the status 'open', see dataset command). As the deployment progresses, sample data and events accumulate within the active dataset.
If logging is stopped (for any reason), the active dataset becomes one of a number of historical datasets retained in memory, and will not be updated any further (reflected by the status 'closed', see dataset command).
The user can delete any historical dataset to increase the amount of memory available for new ones.
Associated command(s):