12.17 Quality of Sensor Data

12.17.1 Description

It is quite popular to transmit observation values of the sensor as a form of time series data in social infrastructure, i.e. factories, power plants, water systems, or railroad systems. In these handling of sensor values, observation value is transmitted with "quality bit", which represents quality of data, i.e. the observation value is valid or not by reference to predefined normal operating condition of the sensor.

The quality bit is used as a quality indicator of observation value of sensor. In other words, it is used as a basis for considering whether the value is usable or not, or how the value should be used.

Here we consider an example case where water is stored in a tank and is conveyed by a pump. The water level of a tank is observed by a sensor, and data collection policy (named data catalogue) is utilized at oneM2M MN to transmit average of 2 observation values. The observation value is not adequate to be utilized when there is any abnormality in the electric power source of the sensor or in controller. The average value is not adequate to be utilized when one of observation values is not adequate. Therefore, information such as "the observation value of sensor of water level lacks quality" is added in order to make the application work as intended.

12.17.2 Source

REQ-2015-0599R03 Sensor Data Quality

12.18.3 Actors

• Tank1: Tank stores water
• Pump1: Pump conveys water
• Water level sensor1: It observes water level of a tank1 and transmit the observation value d1 to PLC/DCS1 at fixed time intervals
• Electric power source of water level sensor1: It supplies electric power which is required for the water level sensor1 to work correctly
• PLC(Programmable Logic Controller)/DCS(Distributed Control System)1: PLC/DCS receives two observation values, i.e. water level of tank1 and status signal of electric power source of water level sensor1, and transmit a form of water level data d1 with a quality bit q1 at fixed time intervals. When the electric power source of water level sensor1 is abnormal or PLC/DCS1 itself has some abnormality, the water level observation value d1 is considered to be incorrect and the quality bit q1 is set to "not good."
• Tank2: Tank stores water
• Pump2: Pump conveys water
• Water level sensor2: It observes water level of tank2 and transmit the observation value d1 to PLC/DCS2 at fixed time intervals
• Electric power source of water level sensor2: It supplies electric power which is required for the water level sensor to work correctly
• PLC/DCS2: PLC/DCS receives two observation values, i.e. water level of tank2 and status signal of electric power source of water level sensor2, and transmit a form of water level data d2 with a quality bit q2 at fixed time intervals. When the electric power source of water level sensor2 is abnormal or PLC/DCS2 itself has some abnormality, the water level observation value d2 is considered to be incorrect and the quality bit q2 is set to "not good."
• oneM2M MN: oneM2M MN receives water level observation values d1 and its corresponding quality bit q1 from PLC/DCS1 as a form of time series data, receives water level observation value d2 and its corresponding quality bit q2 from PLC/DCS2 as a form of time series data, calculates average value d3 as specified by data catalogue, and transmits the average value d3 and its quality bit q3 to oneM2M platform. When quality bit q1 or q2 is "not good", the calculated average d3 is considered to be incorrect and quality bit q3 is set to "not good."
• oneM2M platform: oneM2M platform receives time series data and its corresponding quality bit from oneM2M MN and transmit them to Application.
• oneM2M Application: oneM2M Application receives time series data and its corresponding quality bit, and performs user-defined procedure(s) referring quality bit value.
• Real-time Ethernet: Real-time Ethernet connects PLC/DCS and oneM2M MN.
• Underlying network: connects oneM2M MN and oneM2M platform.

12.17.4 Pre-conditions

Observation value of sensor is coupled with its quality bit and correspondence relation is defined.

12.17.5 Triggers

PLC/DCS receives observation value at fixed time intervals and receives status signal of electric power supply of the water volume sensor.

12.17.6 Normal Flow

1. When the electric power source of water level sensor1 is normal and PLC/DCS1 has no abnormality, the observation value d1 is considered to present correct water level and to be usable and PLC/DCS1 adds quality bit q1 "good" to the observation value d1. Otherwise, when the electric power source of water level sensor 1 is abnormal or PLC/DCS1 has some abnormality, the observation value d1 is considered to be incorrect and PLC/DCS1 adds quality bit q1 "not good" to the observation value d1. Similarly, PLC/DCS2 adds quality bit q2 "good" or "not good" to the observation value d2.
2. oneM2M MN receives observation value d1 and its corresponding quality bit q1 from PLC/DCS1 as a form of time series data receives observation value d2 and its corresponding quality bit q2 from PLC/DCS2 as a form of time series data, calculates average value d3 as specified by data catalogue, and transmits the average value d3 and its quality bit q3 to oneM2M platform. When q1 or q2 is "not good", the calculated average value d3 is considered to be incorrect and quality bit q3 is set to "not good."
3. oneM2M platform receives time series data and its corresponding quality bit from oneM2M MN, and transmits them to oneM2M application.
4. Application receives time series data and its corresponding quality bit from oneM2M platform and performs user-defined procedure(s) referring quality bit value. Usually, observation value with quality bit "not good" is not used to monitoring or controlling functions.

12.17.7 Alternative flow

None.

12.17.8 Post-conditions

None.

12.17.9 High Level Illustration

Figure 12.17.9-1 Quality of sensor data

12.17.10 Potential requirements

1. The oneM2M system shall provide capability to manage data quality description of resource.