SRS Residual Gas Analyzer: MCP Server

Let an AI agent read the residual gas composition of a vacuum system with a Stanford Research Systems RGA100, RGA200 or RGA300 quadrupole mass spectrometer: partial pressures at chosen m/z, analog and histogram spectra, total pressure, helium leak checks and a first-pass identification of the gases (water, hydrogen, nitrogen/CO, oxygen, argon, CO2, hydrocarbons). The filament, the electron multiplier (CDEM) and the ionizer degas are protected by server-side pressure interlocks.

Try it without hardware

uvx labmcp-srs-rga --simulate --check
uvx labmcp-srs-rga --simulate --option scenario=helium_leak    # He pulses every 20 s for leak_check
uvx labmcp-srs-rga --simulate --option scenario=overpressure   # a growing leak trips the filament

The simulator is an RGA200 with a CDEM on an unbaked chamber at ~1e-7 Torr (mostly water, then H2, N2/CO, CO2).

Connect your RGA

1. Cable: the RGA's electronics box (ECU) has a DB-9 RS-232 port wired as DCE with RTS/CTS hardware handshaking. Use a straight-through cable (or a USB-serial adapter) that carries RTS and CTS. The settings are fixed: 28,800 baud, 8 data bits, no parity, 1 stop bit. The server sets these for you.
2. Close RGA Windows / RGA Com (only one program can use the port).
3. Find the port: uvx labmcp ports
4. Test the connection:

   uvx labmcp-srs-rga --address /dev/ttyUSB0 --check          # Linux
   uvx labmcp-srs-rga --address /dev/tty.usbserial-XXXX --check  # macOS
   uvx labmcp-srs-rga --address COM3 --check                  # Windows
   uvx labmcp-srs-rga --address tcp://192.168.1.50:4001 --check   # raw-TCP serial-to-Ethernet adapter
   uvx labmcp-srs-rga --address tcp://192.168.1.50:818 --option user=admin --option password=admin --check  # SRS RGA Ethernet adapter
   

   On connection the server sends ID? and IN0 (clear the RGA's buffers and run its hardware self-check). It does not switch anything on.

Add to your MCP client

Claude Code

claude mcp add rga -- uvx labmcp-srs-rga --address /dev/ttyUSB0

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

{
  "mcpServers": {
    "rga": {
      "command": "uvx",
      "args": ["labmcp-srs-rga", "--address", "/dev/ttyUSB0"]
    }
  }
}

Add --read-only to allow measurements but block switching the filament/CDEM, degassing, calibration and settings changes (the off switches stay available). For other clients, generate the snippet with uvx labmcp config srs-rga --address /dev/ttyUSB0 --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 RGA filament must only run below 1e-4 Torr, and a CDEM should never see voltage above 1e-4 Torr, with 5e-6 Torr or less recommended (manual: FL command warning p. 6-35, "CDEM Handling and Care" in the Maintenance chapter). The RGA only measures pressure while its filament emits, so switching on needs evidence:

• set_filament and degas: the pressure must be at or below max_filament_pressure_torr. set_cdem: at or below max_cdem_pressure_torr, and the voltage at or below max_cdem_voltage_v (the hardware range of 10-2490 V is enforced as well).
• Evidence for all three: external_pressure_torr (a reading from another gauge that the user confirmed) and, when the filament is on and the CDEM off, a total-pressure measurement taken right then. If both are available, the higher one is checked, so a mistyped gauge value can't override what the RGA measures. With the CDEM on (the RGA can't measure), a reading from the last max_pressure_reading_age_s is accepted, but only while the filament is still on: once it is off (switched off or tripped) an older reading says nothing about the present pressure.
• RGA readings used as evidence are scaled to 1 mA emission: the ion current is proportional to the emission current, so a reading at 0.1 mA would otherwise understate the pressure 10x.
• The instrument's own filament protection still applies: an overpressure shuts the emission and the CDEM down (error FL6), and get_status reports it.
• all_off, filament_off and cdem_off interrupt a running scan, mass measurement or leak check (which then returns an error and no data) instead of waiting for it to finish. all_off attempts every step even if one fails, and reports what failed.

Override at launch, e.g. --limit max_cdem_voltage_v=2400 --limit max_filament_pressure_torr=1e-5.

Example prompts

• "The ion gauge reads 2e-7 Torr. Switch the RGA filament on and tell me what's in the chamber."
• "Take a 1-100 amu analog scan, save it to ~/data/rga/after_bake.csv, and compare water and hydrogen with this morning."
• "Is this an air leak? Check 28, 32 and 40 and the ratios."
• "Start a 3-minute helium leak check on m/z 4; I'll spray the flanges one by one after 20 seconds."
• "Switch the CDEM on at 1400 V, measure 2, 4, 18, 28, 44 every minute for 10 minutes, then switch everything off."

Notes

• Wire format. Commands are two letters plus a parameter, ending with CR; ASCII replies end with LF CR. Ion currents from MR, TP? and every scan point are binary 4-byte little-endian two's complement integers in units of 1e-16 A. Hardware commands (IN, FL, HV, EE, IE, VF, CA, CL, DG) answer with the STATUS byte; NF, MI, MF, SA, TP0/1, MR0 answer nothing. The server reads back every silent setting.
• Rejected commands get no reply. The RGA only flashes its error LED and sets RS232_ERR; the server then reads EC? and reports the reason (bad command, bad parameter, parameter conflict).
• Partial pressures are N2-equivalent. The server divides the ion current by the partial-pressure sensitivity SP stored in the head (factory value: N2 at default ionizer settings), and by the stored CDEM gain MG when the CDEM is on. Other gases have different sensitivities (H2 ~0.44, He ~0.14, Ar ~1.2 relative to N2); identify_residual_gases corrects with typical values, the other tools do not. The stored factors are only valid at 70 eV / 12 eV / 90 V and 1 mA emission.
• Total pressure (TP?) is disabled by the RGA while the CDEM is on (it returns 0), and needs the filament on.
• Degas runs inside the RGA and any command aborts it, so degas returns immediately and the server refuses other commands (except filament_off, cdem_off and all_off, which abort it) until it ends.
• Noise floor (NF0-NF7) sets the speed and detection limit: from 2000 ms/amu and ~7e-15 A noise (NF0) to 15 ms/amu and ~5e-13 A (NF7). The factory default is NF4 (126 ms/amu).
• SRS RGA Ethernet adapter login (--option user=... --option password=..., port 818) follows SRS's srsinst.rga driver and has not been tested on hardware. Generic raw-TCP serial servers need no login but must be set to 28,800 baud 8N1 with RTS/CTS.
• After a scan or measure_masses the server switches the quadrupole RF off (MR0), as the manual recommends.
• save_path (scans and leak_check) must end in .csv and must not exist yet: existing files are never overwritten. Missing folders are created, ~ is expanded, and the path is checked before the measurement starts.
• Link recovery. If a scan's binary data doesn't arrive in time (or a safety tool interrupts it), the server discards the partial data, halts the scan with IN0 and waits for its STATUS reply before the next command, so later replies stay in step.

Hardware verification