Digital Multimeter (DMM)#

Using InstroDMM for SCPI-based digital multimeters

InstroDMM provides a unified interface for digital multimeters. This class is initialized with a vendor-specific driver (Agilent34401A, Keysight34461A, Keithley2400, …), and provides the vendor-agnostic API (set_measurement_function, read, set_range, …).

Creating an InstroDMM#

from instro.dmm.drivers import Agilent34401A
from instro.dmm import InstroDMM

dmm = InstroDMM(
    name="myDMM",
    driver=Agilent34401A("ASRL3::INSTR"),
)

Supported Vendors#

Agilent/HP/Keysight 34401A
Agilent34401A
Fluke 8845A
Fluke8845A
Keithley 2400
Keithley2400
Keysight 34461A
Keysight34461A

  • Virtual: no hardware or server; readings simulated in-process (VirtualDMM, see Virtual instruments)

  • Simulated: no hardware required; pairs with the bundled DMM simulator (SimulatedDMM)

If your vendor or model is not listed, see Custom Driver Development, or open a Driver Request issue on GitHub.

Example#

More examples found in Examples

Details#

The following presents details about the InstroDMM. Specific driver details can be found on their pages.

Driver Composition#

An InstroDMM is built from a concrete driver:

InstroDMM("name", driver=Agilent34401A("ASRL3::INSTR"))

  • Agilent34401A owns the connection setup and vendor-specific command mapping.

  • InstroDMM owns the category-level workflow: measurements, commands, publishers, the background daemon.

Lifecycle#

The typical InstroDMM workflow:

  1. Construct: instantiate the vendor driver and pass it to InstroDMM.

  2. open(): establishes the VISA connection.

  3. Configure measurement: set the measurement function (e.g. DC voltage), and optionally resolution, aperture, and range.

  4. read(): trigger a measurement and get the value. The read_<function>() shorthands (e.g. read_dc_voltage()) fold steps 3 and 4 into one call.

  5. close(): disconnect from hardware.

Optionally, you can use background fetching via start() / stop(), but it is an atypical use case for a DMM. See Two ways to get data for more.

Measurement Functions#

InstroDMM supports these measurement functions (availability depends on the driver):

  • DC Voltage

  • AC Voltage

  • DC Current

  • AC Current

  • 2-Wire Resistance

  • 4-Wire Resistance

You must call set_measurement_function() before configuring resolution, aperture, range, or calling read().

Single-call reads#

When you only need a value and don’t need to tune resolution, aperture, or range, use the per-function shorthand instead of the two-step sequence:

voltage = dmm.read_dc_voltage()  # selects DC voltage if needed, then reads

One exists per measurement function: read_dc_voltage(), read_ac_voltage(), read_dc_current(), read_ac_current(), read_resistance() (2-wire), and read_four_wire_resistance().

Each selects the function only when it isn’t already active, so repeated calls in the same function cost a single measurement and publish set_measurement_function.cmd once. They publish exactly the same channels as set_measurement_function() + read().

Init from a Config File#

InstroDMM can also be constructed directly from a JSON config file, which removes the need to write any Python setup code:

from instro.dmm import InstroDMM

dmm = InstroDMM(config="bench_dmm.json")

Where bench_dmm.json contains:

{
  "version": 1,
  "instrument": "InstroDMM",
  "device": {
    "name": "bench_dmm",
    "description": "Bench multimeter",
    "manufacturer": "Keysight",
    "model": "34461A"
  },
  "driver": {
    "name": "Keysight34461A",
    "connection_type": "visa",
    "visa": {
      "visa_resource": "USB0::0x2A8D::0x1301::MY12345678::INSTR"
    }
  },
  "measurement": {
    "function": "DC_VOLTAGE",
    "aperture_nplc": 10,
    "range": 10.0
  },
  "timing": {
    "poll_interval": 1.0
  },
  "publishers": [
    {
      "type": "NominalCorePublisher",
      "dataset_rid": "<dataset_rid>"
    }
  ]
}

To try a config with no hardware, use the virtual driver: "driver": {"connection_type": "virtual", "name": "VirtualDMM"}.

See Config Files for the full field reference.

Custom Driver Development#

For more information on writing a custom driver, see Custom Driver Development.