Limits Introduction

The ait.core.limits module provides support for specifying acceptable value ranges for telemetry fields.

Consider the below example telemetry packet and fields for which we’ll specify limit values.

- !Packet
  name: 1553_HS_Packet
  desc: Ethernet 1553 packet used to monitor telemetry in real-time
  functions: CurrA_Fx(dn):   (dn - 2) / 1234.0

    - !Field
      name: Voltage_A
      desc: Voltage A as a 14-bit DN.  Conversion to engineering units is TBD.
      units: Volts
      type: MSB_U16

    - !Field
      name: product_type
      type: U8
        0: TABLE_FOO
        1: TABLE_BAR
        2: MEM_DUMP


Limits are expected to be specified in Engineering Units when a given telemetry field has a corresponding DN-to-EU conversion. A field’s value is converted via it’s DN-to-EU function if present prior to limit checks.

Specifying Limits

Limit values can be specified for fields with a value range and for fields with enumerated values. By default, limits are specified in limits.yaml. You can see the path specified in config.yaml under the limits.filename parameter.

    filename:  limits.yaml

Value-Range Limits

For the 1553_HS_PACKET.Voltage_A field we’ll specify min/max value ranges for our limits. You’ll see in the example below that we’re specifying upper and lower bounds with error and warning values for each. You can customize the limits as necessary by specify a subset of these values. For instance, you could specify just a lower warning bound if that is all you were concerned about.

- !Limit
  source: 1553_HS_Packet.Voltage_A
  desc: Voltage A
  units: Volts
    error: 5.0
    warn: 10.0
    error: 45.0
    warn: 40.0

Enum Limits

For fields with enumerated values, such as the 1553_HS_PACKET.product_type field, we specify warning and error limits for one or more of the field’s enumerated values. Here we’re specifying an error limit when the field has the MEM_DUMP value and a warning limit when the field value is either TABLE_FOO or TABLE_BAR.

- !Limit
  source: 1553_HS_PACKET.product_type
  desc: Ethernet Product Type field
    error: MEM_DUMP
      - TABLE_FOO
      - TABLE_BAR