Modbus data fields

Version 3.0 of the API introduces the /modbus/* endpoints, which return raw data collected from the registers of supported modbus meters, such as the CETA PMC-220 (single phase) and PMC-340B (3 phase) NMI pattern approved meters.

Cumulative data

Note that the energy values (kWh_*) returned by the PMC devices are cumulative data values, not interval data. This differs from the Wattwatchers Long and Short energy values returned by the API.

kWh

Real energy data is returned in units of 0.01 kWh, not Joules, which differs from the Wattwatchers Long and Short real energy values returned by the API.

kVAh

Reactive energy data is returned in units of 0.01 kVAh, not Joules, which differs from the Wattwatchers Long and Short reactive energy values returned by the API.

Lists vs. indvidual entries

Retrieving data from the /modbus/{device-id} endpoint returns a list of entries matching the specified fromTs and toTs timestamp values, e.g. [{ <object 1 values> }, { <object 2 values> }, etc. ]

Retrieving data from the /modbus/{device-id}/latest or /modbus/{device-id}/first endpoints will return a single JSON object, e.g. { <object values> }.

No data

If there is no data for a device (i.e. it's uninitialised) or the device you are calling the /modbus/* endooint for is not a modbus device, a 204 No Data response will be returned.

If a device has data, but the query parameters specified don't match any data, an empty list (e.g. []) will be returned for the /modbus/{device-id} endpoint.

Non-modbus device

If you attempt to request modbus data (using the /modbus/{device-id} endpoint) for a device that doesn't support modbus data, you will get a 422 Unprocessable Entity status response:

{
    "code": "UNPROCESSABLE ENTITY",
    "httpCode": 422,
    "message": "You have attempted to query modbus data for a device ID that does not support it"
}

Common data object values

The following fields are present in data from both the PMC-220 and PMC-340B devices.

Property	Data type	Units	Notes
kVAh	Int	0.01 kVAh	Apparent power
kWh_Exp	Int	0.01 kWh	Real energy export
kWh_Imp	Int	0.01 kWh	Real energy import
kWh_Net	Int	0.01 kWh	Real energy net
kWh_Tot	Int	0.01 kWh	Real energy total
kvarh_Q1	Int	0.01 kvarh	kvarh of Q1
kvarh_Q2	Int	0.01 kvarh	kvarh of Q2
kvarh_Q3	Int	0.01 kvarh	kvarh of Q3
kvarh_Q4	Int	0.01 kvarh	kvarh of Q4
kvarh_Imp	Int	0.01 kvarh	kvarh import
kvarh_Exp	Int	0.01 kvarh	kvarh export
kvarh_Net	Int	0.01 kvarh	kvarh net
kvarh_Tot	Int	0.01 kvarh	kvarh total
model	String	N/A	The device model that was attached to the device at the time the data was collected. Can be used to determine what the payload structure is. Currently only PMC-220 and PMC-340B values are supported.
timestamp	Int	Seconds since Unix epoch	The Unix timestamp when the data was captured on the device.

PMC-220 object values

Example data entry

{
  "_I": 0.3065536916255951,
  "_PF": 0.5856215357780457,
  "_V": 245.0169219970703,
  "kVAh": 616,
  "kWh_Exp": 0,
  "kWh_Imp": 283,
  "kWh_Net": 283,
  "kWh_Tot": 283,
  "kvarh_Exp": 173,
  "kvarh_Imp": 0,
  "kvarh_Net": -173,
  "kvarh_Tot": 173,
  "model": "PMC-220",
  "timestamp": 1546956000
}

PMC-220 specific fields

Property	Data type	Units	Notes
_I	Float	Amperes	The Current value
_PF	Float	-	The Power Factor value
_V	Float	Volts	The Voltage value

PMC-340B object values

{
  "_Ia": 0.0,
  "_Ib": 0.0,
  "_Ic": 0.0,
  "_PFa": 1.0,
  "_PFb": 1.0,
  "_PFc": 1.0,
  "_Uan": 244.8056182861328,
  "_Ubn": 122.43417358398438,
  "_Ucn": 122.45341491699219,
  "kVAh": 0,
  "kWh_Exp": 0,
  "kWh_Imp": 0,
  "kWh_Net": 0,
  "kWh_Tot": 0,
  "kWh_Exp_a": 0,
  "kWh_Exp_b": 0,
  "kWh_Exp_c": 0,
  "kWh_Imp_a": 1355,
  "kWh_Imp_b": 0,
  "kWh_Imp_c": 0,
  "kvarh_Q1": 0,
  "kvarh_Q2": 0,
  "kvarh_Q3": 0,
  "kvarh_Q4": 0,
  "kvarh_Exp": 0,
  "kvarh_Imp": 0,
  "kvarh_Net": 0,
  "kvarh_Tot": 0,
  "model": "PMC-340B",
  "timestamp": 1546952400
}

PMC-340B specific fields

The PMC-340B device returns three-pase data. Where relevant, values for each phase is labeled with an a, b or c suffix.

Property	Data type	Units	Notes
_Ia, _Ib, _Ic	Float	Amperes	The Current value for the relevant phase.
_PFa, _PFb, _PFc	Float	-	The Power Factor value for the relevant phase.
_Uan, _Ubn, _Ucn	Float	Volts	The phase-neutral Voltage value for the relevant phase.
kWh_Imp_a, kWh_Imp_b, kWh_Imp_c	Int	0.01 kWh	Imported total energy value for the relevant phase.
kWh_Exp_a, kWh_Exp_b, kWh_Exp_c	Int	0.01 kWh	Exported total energy value for the relevant phase.