Config Files#

Constructing instruments from JSON config files instead of Python setup code

Every config-driven category (InstroPSU, InstroDMM, InstroELoad, InstroAWG, InstroScope, …) can be constructed directly from a JSON config file, a plain dict, or an already-built config object, instead of driver=... Python setup code:

psu = InstroPSU(config="bench_psu.json")
psu = InstroPSU(config={"device": {"name": "bench_psu"}, "driver": {...}, ...})
psu = InstroPSU(config=my_psu_config)

config is mutually exclusive with driver/num_channels. A passed-in config object is copied up front, so later edits to the object you passed don’t reach the instrument.

Shape shared by every category#

{
  "version": 1,
  "instrument": "InstroPSU",
  "device": {
    "name": "bench_psu",
    "description": "Bench channel 1 supply",
    "manufacturer": "B&K Precision",
    "model": "9115"
  },
  "driver": {
    "name": "BK9115",
    "num_channels": 1,
    "connection_type": "visa",
    "visa": { "visa_resource": "USB0::0x2A8D::0x0101::MY12345::INSTR" }
  },
  "timing": { "poll_interval": 1.0 },
  "publishers": [
    { "type": "NominalCorePublisher", "dataset_rid": "<dataset_rid>" }
  ]
}

  • device.name is required and used as the channel-name prefix when publishing. description, manufacturer, and model are optional descriptive metadata about the physical instrument.

  • driver.name must match one of that category’s registered vendor/model keys. The visa block accepts every VisaConfig field, so a non-default backend, timeout, or serial setting can be set from JSON too.

  • driver.num_channels is required by the multi-channel categories (PSU, Scope, AWG) and rejected by the single-channel ones (DMM, ELoad). The driver block is category-specific, not a shared component: each category validates it strictly, so a config copied between categories will not validate unchanged.

  • timing.poll_interval is optional and sets the background daemon’s polling interval. Some categories require an initial-state block to be present before timing is meaningful (see each category below).

  • publishers is optional and accepts a list of NominalCorePublisher and/or FilePublisher entries, each tagged by type.

  • autostart=True opens the connection and starts background polling immediately: InstroPSU(config="bench_psu.json", autostart=True).

  • Every category’s config model is validated strictly: fields outside the documented set are rejected, so there’s no **kwargs-style escape hatch from JSON. Set default tags via the direct Python constructor instead.

Options the concrete driver doesn’t support raise NotImplementedError when the config is applied, exactly as the equivalent runtime call would.

Category-specific state blocks#

Beyond the shared shape above, some categories accept an optional block that sets initial instrument state through the same public setters a manual call would use, so it publishes the same .cmd channels.

PSU#

InstroPSU’s config has no initial-state block — only device, driver, timing, and publishers. See the PSU guide for a full example.

DMM#

An optional measurement block:

  • function (required within the block): one of DC_VOLTAGE, AC_VOLTAGE, DC_CURRENT, AC_CURRENT, TWO_WIRE_RESISTANCE, FOUR_WIRE_RESISTANCE.

  • digits: resolution in digits. Omit to keep the instrument default. Driver support varies: the Agilent 34401A accepts it, while the Keysight 34461A rejects it in favor of aperture_nplc.

  • aperture_nplc / aperture_seconds: integration time, in power-line cycles or seconds. At most one of the two.

  • range: a number for a manual range in the function’s units, or "auto" for auto-range. Omit to keep the instrument default.

Because background polling cannot start without a measurement function, a config that declares timing must also declare measurement.

ELoad#

An optional load block:

  • mode (required within the block): one of CC, CV, CP, CR. Required because level and range cannot be set before a mode.

  • level: operating level in the mode’s units (CC: A, CV: V, CP: W, CR: Ω). Omit to keep the instrument default.

  • range: operating range in the mode’s units. Driver support for range on CP/CR modes varies by vendor.

  • slew_rate: {"direction": "RISE" | "FALL" | "BOTH", "rate": <A/µs>}, mapping to set_slewrate.

Note

The config never enables the input. The load block pre-arms the setpoint; enabling the input stays an explicit runtime call (eload.output_enable(True)). The polled measurements (get_voltage, get_current) work regardless of mode, so timing is valid without a load block for passive monitoring.

AWG#

A required, non-empty channels dict, keyed by channel number as a string. Each entry is applied once per session on open() (a close() + open() cycle reapplies it):

  • waveform (required): one of sine, square, sawtooth, triangle, pulse, arbitrary, or static_value, discriminated by a shape field. arbitrary’s samples accepts an inline array of at least 2 floats normalized to [-1.0, 1.0], or a string path to a CSV file (read fresh on every open(); a relative path resolves against the process’s working directory, not the config file).

  • amplitude (optional): {"value": <float>, "unit": "VPP" | "VP" | "VRMS" | "DBM"}; unit defaults to VPP.

  • offset (optional): DC offset in volts.

  • modulation / burst / sweep (optional): at most one may carry "enable": true per channel. See set_modulation, set_burst*, set_sweep* for the field semantics.

output_enable cannot be set from the config; call awg.output_enable(channel, True) explicitly after open().

Scope#

Optional channels, acquisition, and trigger blocks, applied through the public setters when open() runs, in dependency order (coupling/attenuation before scale, trigger before acquisition, average_count before mode). If acquisition.start_acquisition_on_open is set, run() fires before the acquisition block applies, since some scopes only accept acquisition-mode changes while running.

  • channels: per-channel initial state keyed by 1-based channel number. Accepts vertical_scale, vertical_offset, coupling ("AC"/"DC"), probe_attenuation, and a measurements list to poll from the background daemon.

  • acquisition: mode, average_count (requires mode: "AVERAGE"), horizontal_scale, start_acquisition_on_open (default false).

  • trigger: source (required within the block), type, level, slope, mode.

After the blocks apply, open() calls sync_configuration() and logs one warning per field the instrument reports differently from the config (scopes snap requested values to the nearest supported step). Trigger fields are not checked, since sync_configuration() does not read them back. autostart (host-side daemon) and acquisition.start_acquisition_on_open (instrument acquiring) are independent knobs.

See the Scope guide for a full example.