Sensor Interfaces
The primary purpose of CFE is to provide you with an interface to create, edit and remove sensor data feeds inside SCS. When a new sensor is brought online you can describe it physically via the Physical Devices portion of CFE, but in order for SCS to actually start ingesting, recording and disseminating the data being provided from the sensor you must also add it to the Sensor Interfaces portion of CFE.
The Sensor Interface portion of the tree breaks each interface down in a hierarchy, each level of this hierarchy is described in the following paragraphs.
If your interface is linked to a physical device then it will be grouped inside the 'type' of physical device to help with organization.
In this instance you can see we have a Sensor Interface defining the data coming in on COM port 37.
It is defining the data coming from the ADCP-2129 Physical Device.
It has a single message definition describing the $VDVBW data
It breaks the $VDVBW data stream into six (6) data fields.
Interface Level
A Sensor Interface encapsulates the interface of a physical device to ACQ. You can also think of it as describing the source of a physical device’s messages, without knowing anything about the physical device itself. A sensor interface has parameters such as the baud rate, TCP/IP port and others that further describe the interface.
SCS has four (4) Sensor Interface types, each one distinct in how it is interfaced to its data source.
- COM: Connects to its physical device via a COM port using the RS-232 protocol. A COM device receives messages without prompting the physical device.
- Polled COM: Same as a COM device, except the physical device sends a message only when ACQ prompts it to.
- Network: Connects to a physical device over a network using a TCP or UDP protocol.
- Manual: The physical device is a keyboard that passes data to ACQ over a TCP connection. The Manual Interfaces SCS Widget allows the user to send observational data from their keyboard to ACQ for logging, display, etc.
When you configure sensor interfaces, you are specifying the following:
- What sensor equipment is connected to SCS
- The source of the sensor data (COM port, network socket, keyboard entry, etc.)
- What messages the sensors are supplying
- How each message is divided into data fields
- How the sensor data will be displayed in real time
- How SCS will log the data to disk.
Message Definition Level
Each Sensor Interface may deliver multiple distinct messages that are transmitted from the Physical sensor. Message definitions define all of the information needed to acquire a specific message from a physical sensor. A sensor may transmit multiple messages with each being described separately. Message definitions are sometimes closely coupled with the kind of Sensor Devices and other times message definitions are re-used by multiple Sensor Interfaces.
A Sensor Interface may contain multiple message definitions such as a GPS receiver that may be sending multiple NMEA messages (GGA, VTG, etc.)
SCS has three (3) main types of Message Definitions.
- Delimited: The data fields inside the RAW stream are delimited via one or more ASCII characters (comma, tab, etc).
- Fixed: The data fields inside the RAW stream are defined by hard and fixed character positions.
- NMEA: A special implementation of Delimited, message and data fields comply with the NMEA-0183 standard.
Data Field Level
Every Sensor Interface passes one or more Message Definitions to ACQ. Each message in turn has one or more data fields associated with it, one for each measurement that the physical device makes. Each data field has parameters that establish how to decode and monitor one measurement in the message. These parameters specify such things as where the measurement is in the message, what units it has and what type of measurement it is.
Once ACQ isolates a data field it can pass on the value to other SCS apps that can display them, pass them on for derived sensor calculations, or use them in other ways described in later chapters. Since serial messages have fixed format, serial data fields are delimited by their start and end character positions in the message. NMEA Messages are variable length where the data fields are delimited by a comma. NMEA data fields may also be attributed special features of translation to allow a code embedded in the message to be translated to a more meaningful value.