Keithley SourceMeter SMU — MCP Server

Let an AI agent source voltage or current with a compliance limit, measure V and I, and run bounded IV sweeps (linear, log, dual) on Keithley (Tektronix) SourceMeter SMUs. Every sweep ends with the output switched off, even when something goes wrong. The server speaks all three Keithley remote dialects: 2400-series SCPI, 2450-family SCPI, and 2600B TSP.

Try it without hardware

uvx labmcp-keithley-smu --simulate --check                                   # 2450 + 1 kΩ resistor
uvx labmcp-keithley-smu --simulate --option dialect=2600 --option sim_dut=diode --check
uvx labmcp-keithley-smu --simulate --option dialect=2400 --option sim_resistance_ohm=47 --check

The simulated DUT is a resistor (1 kΩ by default) or a 1N4148-like diode (Shockley equation, I_s = 2.52 nA, n = 1.752, R_s = 0.568 Ω). Compliance clamping behaves as on a real SMU.

Connect your SMU

1. Instrument side.
   • 2400 series: GPIB (default address 24) or RS-232. For RS-232 set MENU > COMMUNICATION > RS-232: 9600 baud, 8 data bits, no parity, TERMINATOR LF, no flow control.
   • 2450 / 2460 / 2461 / 2470: use the SCPI command set (MENU > System > Settings > Command Set > SCPI, then reboot). If the instrument is in TSP mode the server stops with instructions. In SCPI2400 emulation mode it is driven with the 2400 dialect. Above ±21 V the 2450 needs its safety interlock closed.
   • 2600B: works as shipped (TSP). Leave localnode.prompts disabled (the default); prompts would be mixed into replies.
2. Find the address: uvx labmcp ports (or python -m pyvisa info). GPIB and USBTMC need a VISA library with GPIB support. NI-VISA works everywhere; pyvisa-py covers USBTMC/LAN (and GPIB with gpib-ctypes/linux-gpib).
3. Test the connection:
   bash

   uvx labmcp-keithley-smu --address GPIB0::24::INSTR --check
   uvx labmcp-keithley-smu --address USB0::0x05E6::0x2450::04096331::INSTR --check
   uvx labmcp-keithley-smu --address tcp://192.168.1.50:5025 --check             # 2450 / 2600B LAN
   uvx labmcp-keithley-smu --address TCPIP0::192.168.1.51::inst0::INSTR --option channel=b --check   # 2602B, SMU B
   

   The dialect is detected from *IDN? (and *LANG? on the 2450 family). Force it with --option dialect=2400|2450|2600.

Add to your MCP client

Claude Code

claude mcp add smu -- uvx labmcp-keithley-smu --address GPIB0::24::INSTR --limit max_voltage_v=5 --limit max_current_a=0.02

Claude Desktop / Cursor / Windsurf (claude_desktop_config.json, .cursor/mcp.json, …)

{
  "mcpServers": {
    "smu": {
      "command": "uvx",
      "args": ["labmcp-keithley-smu", "--address", "USB0::0x05E6::0x2450::04096331::INSTR",
               "--limit", "max_voltage_v=5", "--limit", "max_current_a=0.02"]
    }
  }
}

Add --read-only to allow status and measurements but block configuration, output-on and sweeps (output_off stays available). For other clients, generate the snippet with uvx labmcp config keithley-smu --address <resource> --client vscode (also cursor, codex, claude-code).

Tools

get_connection_info, get_command_log and reconnect are built into every LabMCP server.

Safety limits

The limits are checked before anything is sent: by configure_source and set_source_level, by run_iv_sweep (on the largest |start|, |stop|), and by output_on, which reads the programmed level and compliance back from the instrument. A level set on the front panel is therefore caught too. Requests beyond the model's own maximum (e.g. 40 V on a 2602B) are also refused. Override at launch: --limit max_voltage_v=60 --limit max_power_w=10. Tighten the defaults for fragile DUTs.

Example prompts

• "Measure the IV curve of this LED from 0 to 3 V in 61 steps with a 20 mA compliance, then tell me the turn-on voltage at 1 mA."
• "Source 1 mA through the sample in 4-wire mode and give me its resistance; then turn the output off."
• "Run a dual sweep from −1 V to +1 V on the memristor with 1 mA compliance and 0.1 s per point, and save it to ~/data/memristor_run3.csv."
• "Do a log current sweep from 1 nA to 10 mA on the photodiode with a 2 V limit and fit the ideality factor."
• "What is the SMU doing right now? If the output is on, turn it off."

Notes

• Simple, verifiable commands. Sweeps are stepped loops: set the level, wait delay_s, take one reading, check compliance. Built-in instrument sweeps and trigger models are not used, so every point shows up in get_command_log. The output is switched off in a try/finally at the end of every sweep. Calling output_off while a sweep runs (even while it is still configuring) sets an abort flag and switches the output off at once; the sweep then stops without switching the output on again and reports aborted: true.

• Sweep duration. Besides max_sweep_duration_s, one sweep can take at most 1740 s (the tool's 30-minute timeout minus a margin): longer estimates are refused, and a sweep that runs slower than estimated stops early with the output off and returns the points measured so far (stop_reason says why).

• save_path must end in .csv and must not exist yet (an existing file is never overwritten); missing folders are created. It is checked before the output is switched on.

• Overflow readings (the SMU's +9.9E37 marker) are returned as null in the sweep curve, counted in overflow_points and left out of the statistics and the fit; measure reports them as an error.

• What is measured.

  • 2400: concurrent V and I (:SENS:FUNC:CONC ON, :SENS:FUNC "VOLT","CURR"), read with :READ? (:FORM:ELEM VOLT,CURR,STAT). Compliance comes from status-word bit 3.
  • 2450: the measure function is the non-sourced quantity, source readback is on, and :READ? "defbuffer1",SOUR,READ returns both. Compliance comes from :SOUR:VOLT:ILIM:TRIP? / :SOUR:CURR:VLIM:TRIP?.
  • 2600B: print(smuX.measure.iv()) and print(smuX.source.compliance).

  In compliance, the reported V and I are the measured values, not the programmed level.

• The 2400's :MEAS? turns the output on by itself (manual p. 18-72), so it is never used. measure refuses to run when the output is off.

• Reconfiguration happens with the output off. configure_source and set_4wire refuse while the output is on. Use set_source_level (a hazard tool) to change a running source.

• Output-off state (normal / zero / high-Z / guard) is left as configured on the instrument. With the default normal state, a current source turned off becomes a 0 V source. For batteries, charged capacitors or solar cells, select high-impedance first (2450 manual p. 6-40).

• The 2460/2461/2470 maxima are not built in (their manuals weren't reviewed). The safety limits still apply, and the instrument rejects anything beyond its range. The 2430 pulse mode and the 2600B's limitp power compliance are not used.

• Timing: NPLC sets the integration time (1 PLC = 16.7 ms at 60 Hz, 20 ms at 50 Hz). Source auto-delay stays at the instrument default (on), and delay_s adds settling time per point.

• Simulator error replies follow the manuals' error lists (+802 "Not permitted with OUTPUT off", -222, -113; 2600B 1101 "Parameter too big", -285/-286). The exact message wording on real firmware may differ.

Hardware verification