Use pymeasure Drivers

When a pymeasure driver exists for an instrument, mcpyvisa can validate parameters before they reach the hardware, parse typed responses, and expose high-level methods that encode multi-step SCPI sequences. Four additional tools become available: instrument_inspect, instrument_get, instrument_set, and instrument_call. The raw instrument_query and instrument_write tools remain as fallback for everything else.

Install pymeasure support

pymeasure is an optional dependency. Install it with:

uv add mcpyvisa[pymeasure]

Once installed, the four pymeasure tools are automatically registered at server startup.

Check if an instrument has a driver

Call instrument_inspect to discover whether a pymeasure driver is available for a given instrument:

> Inspect the DMM

The LLM calls instrument_inspect("dmm"). If a driver exists, the response lists categorized properties and methods:

pymeasure driver: keithley-2000 (Keithley2000)
Instrument: dmm (GPIB0::22::INSTR on bench-a)

Use instrument_get/instrument_set/instrument_call for validated access.

## Measurements (read-only -- triggers a measurement)
  - `voltage`  (SCPI: :MEAS:VOLT:DC?) -- DC voltage measurement
  - `current`  (SCPI: :MEAS:CURR:DC?) -- DC current measurement
  ...

## Controls (read + write -- get/set with validation)
  - `voltage_range`  (SCPI: :SENS:VOLT:DC:RANG / :SENS:VOLT:DC:RANG %g)
    Valid: [0.1, 1, 10, 100, 1000]
    Validator: strict_discrete_set
  ...

You can also use a VISA resource string instead of an alias:

instrument_inspect("GPIB0::22::INSTR")

If no driver is available:

No pymeasure driver available for instrument "dmm" (GPIB0::22::INSTR).

Use instrument_query() and instrument_write() for raw SCPI access.

Supported instruments with pymeasure drivers:
  - hp-33120a: pymeasure.instruments.hp.HP33120A
  - hp-34401a: pymeasure.instruments.hp.HP34401A
  ...

Supported instruments

Instrument	pymeasure Class	Category
HP 33120A	HP33120A	Function Generator
HP 34401A	HP34401A	Multimeter
HP 3478A	HP3478A	Multimeter
HP 8657B	HP8657B	Signal Generator
Agilent 4284A	Agilent4284A	LCR Meter
Keithley 2000	Keithley2000	Multimeter
Keithley 2400	Keithley2400	Source-Measure Unit
Keithley 6517B	Keithley6517B	Electrometer

Note

Driver matching is automatic. mcpyvisa parses the *IDN? response and maps manufacturer/model patterns to the correct pymeasure class. You do not need to specify which driver to use.

Read measurement properties

Measurement properties are read-only and trigger an actual measurement on the instrument. They are not cached values.

> Read the voltage from the DMM

The LLM calls instrument_get("dmm", "voltage"):

voltage = 12.0045

The pymeasure driver sends the appropriate SCPI query, parses the response, and returns a typed Python value. No manual string parsing needed.

Read control properties

Control properties are read/write. Reading one queries the instrument’s current setting without triggering a measurement.

> What voltage range is the DMM set to?

The LLM calls instrument_get("dmm", "voltage_range"):

voltage_range = 100

This tells you the instrument is currently configured for the 100V range. The instrument is not disturbed — it just reports its setting.

Set control properties

Use instrument_set to change a control property. The pymeasure driver validates the value against its defined constraints before sending anything to the instrument.

> Set the voltage range on the DMM to 10

The LLM calls instrument_set("dmm", "voltage_range", "10"):

Set voltage_range = 10

What happens with invalid values

If you pass a value outside the driver’s allowed set:

> Set the voltage range on the DMM to 50

The LLM calls instrument_set("dmm", "voltage_range", "50"):

Validation error for 'voltage_range' = '50': 50 is not in the discrete set [0.1, 1, 10, 100, 1000]

The instrument never receives the command. The pymeasure validator (strict_discrete_set, truncated_range, strict_range) rejects the value before it reaches the bus.

Tip

Run instrument_inspect first to see the valid values and validator type for each control property. The Valid: and Validator: lines tell you exactly what the driver will accept.

Call instrument methods

Methods encode multi-step operations that would otherwise require manually constructing several SCPI commands in sequence.

Apply a voltage source

> Apply 5V with 100mA compliance on the Keithley 2400

The LLM calls instrument_call("smu", "apply_voltage", '{"voltage": 5.0, "compliance_current": 0.1}'):

Called apply_voltage(voltage=5.0, compliance_current=0.1)

Internally, the pymeasure driver configures the source mode, sets the voltage, sets the compliance limit, and enables the output — all from a single method call.

Shut down an output

> Shut down the Keithley 2400

The LLM calls instrument_call("smu", "shutdown"):

Called shutdown()

Caution

Always call shutdown when you are done with source-measure units. This disables the output and returns the instrument to a safe state. Leaving a voltage or current source enabled unattended can damage the device under test.

The kwargs_json parameter accepts a JSON string. For methods with no arguments, omit it or pass "{}". For methods with arguments, pass a JSON object:

'{"voltage": 5.0, "compliance_current": 0.1}'

Fall back to raw SCPI

When no pymeasure driver exists for an instrument, use instrument_query and instrument_write directly. The pymeasure-guided prompt guides this decision.

> Inspect the function generator

The LLM calls instrument_inspect("funcgen"):

No pymeasure driver available for instrument "funcgen" (GPIB0::14::INSTR).

Use instrument_query() and instrument_write() for raw SCPI access.

From here, use instrument_query and instrument_write:

instrument_query("funcgen", "MEAS:VOLT:DC?")     -> +4.56789012E+00
instrument_write("funcgen", "CONF:VOLT:DC 10,0.001")
instrument_query("funcgen", "READ?")              -> +4.56789012E+00

Note

The pymeasure-guided prompt automates this decision. It calls instrument_inspect first, uses validated tools if a driver is available, and falls back to raw SCPI if not.

Combine pymeasure and raw SCPI

You can use both approaches on the same instrument. pymeasure handles the common operations; raw SCPI handles instrument-specific commands the driver does not cover.

For example, on a Keithley 2400 configured as alias "smu":

# Use pymeasure for standard configuration
instrument_set("smu", "source_mode", "voltage")
instrument_set("smu", "source_voltage", "5.0")

# Use raw SCPI for a command the pymeasure driver doesn't expose
instrument_write("smu", ":SYST:BEEP:STAT OFF")

# Read a measurement through pymeasure
instrument_get("smu", "current")

The pymeasure driver and raw SCPI tools share the same backend connection. Commands are serialized through the backend lock regardless of which tool sends them.