Input definitions for detector models in AWS IoT Events - AWS IoT Events

Input definitions for detector models in AWS IoT Events

We want to create one detector model that we can use to monitor and control the temperature in several different areas. Each area can have several sensors that report the temperature. We assume each area is served by one heating unit and one cooling unit that can be turned on or off to control the temperature in the area. Each area is controlled by one detector instance.

Because the different areas we monitor and control might have different characteristics that demand different control parameters, we define the 'seedTemperatureInput' to provide those parameters for each area. When we send one of these input messages to AWS IoT Events, a new detector model instance is created that has the parameters we want to use in that area. Here's the definition of that input.

CLI command:


aws iotevents create-input --cli-input-json file://seedInput.json

File: seedInput.json

{
  "inputName": "seedTemperatureInput",
  "inputDescription": "Temperature seed values.",
  "inputDefinition": {
    "attributes": [
      { "jsonPath": "areaId" },
      { "jsonPath": "desiredTemperature" },
      { "jsonPath": "allowedError" },
      { "jsonPath": "rangeHigh" },
      { "jsonPath": "rangeLow" },
      { "jsonPath": "anomalousHigh" },
      { "jsonPath": "anomalousLow" },
      { "jsonPath": "sensorCount" },
      { "jsonPath": "noDelay" }
    ]
  }
}

Response:

{
    "inputConfiguration": {
        "status": "ACTIVE", 
        "inputArn": "arn:aws:iotevents:us-west-2:123456789012:input/seedTemperatureInput", 
        "lastUpdateTime": 1557519620.736, 
        "creationTime": 1557519620.736, 
        "inputName": "seedTemperatureInput", 
        "inputDescription": "Temperature seed values."
    }
}
Notes

  • A new detector instance is created for each unique 'areaId' received in any message. See the 'key' field in the 'areaDetectorModel' definition.

  • The average temperature can vary from the 'desiredTemperature' by the 'allowedError' before the heating or cooling units are activated for the area.

  • If any sensor reports a temperature above the 'rangeHigh', the detector reports a spike and immediately starts the cooling unit.

  • If any sensor reports a temperature below the 'rangeLow', the detector reports a spike and immediately starts the heating unit.

  • If any sensor reports a temperature above the 'anomalousHigh' or below the 'anomalousLow', the detector reports an anomalous sensor reading, but ignores the reported temperature reading.

  • The 'sensorCount' tells the detector how many sensors are reporting for the area. The detector calculates the average temperature in the area by giving the appropriate weight factor to each temperature reading it receives. Because of this, the detector won't have to keep track of what each sensor reports, and the number of sensors can be changed dynamically, as needed. However, if an individual sensor goes offline, the detector won't know this or make allowances for it. We recommend that you create another detector model specifically for monitoring the connection status of each sensor. Having two complementary detector models simplifies the design of both.

  • The 'noDelay' value can be true or false. After a heating or cooling unit is turned on, it should remain on for a certain minimum time to protect the integrity of the unit and lengthen its operating life. If 'noDelay' is set to false, the detector instance enforces a delay before it turns off the cooling and heating units, to ensure that they are run for the minimum time. The number of seconds of delay has been hardcoded in the detector model definition because we are unable to use a variable value to set a timer.

The 'temperatureInput' is used to transmit sensor data to a detector instance.

CLI command:


aws iotevents create-input --cli-input-json file://temperatureInput.json

File: temperatureInput.json

{
  "inputName": "temperatureInput",
  "inputDescription": "Temperature sensor unit data.",
  "inputDefinition": {
    "attributes": [
      { "jsonPath": "sensorId" },
      { "jsonPath": "areaId" },
      { "jsonPath": "sensorData.temperature" }
    ]
  }
}

Response:

{
    "inputConfiguration": {
        "status": "ACTIVE", 
        "inputArn": "arn:aws:iotevents:us-west-2:123456789012:input/temperatureInput", 
        "lastUpdateTime": 1557519707.399, 
        "creationTime": 1557519707.399, 
        "inputName": "temperatureInput", 
        "inputDescription": "Temperature sensor unit data."
    }
}
Notes

  • The 'sensorId' isn't used by an example detector instance to control or monitor a sensor directly. It's automatically passed into notifications sent by the detector instance. From there, it can be used to identify the sensors that are failing (for example, a sensor that regularly sends anomalous readings might be about to fail), or that have gone offline (when it's used as an input to an additional detector model that monitors the device's heartbeat). The 'sensorId' can also help identify warm or cold zones in an area if its readings regularly differ from the average.

  • The 'areaId' is used to route the sensor's data to the appropriate detector instance. A detector instance is created for each unique 'areaId' received in any message. See the 'key' field in the 'areaDetectorModel' definition.