Alicat Mass Flow & Pressure Controller — MCP Server

Let an AI agent read gas flow, pressure and temperature, set flow or pressure setpoints, switch the gas calibration, tare, and hold or close valves on Alicat Scientific mass flow meters and controllers and pressure controllers through Alicat's documented ASCII serial protocol.

Try it without hardware

uvx labmcp-alicat --simulate --check

The simulator is an MC-500SCCM-D on firmware 10v20 flowing N2, with a first-order flow response, a small sensor zero offset (remove it with tare_flow) and realistic data frames.

Connect your instrument

1. Instrument setup: the factory settings are unit ID A, 19200 baud, 8 data bits, no parity, 1 stop bit, no flow control (MENU → SETUP → RS-232 Serial / RS-485 Serial). If several devices share one RS-485 port, give each a different unit ID. The device must be in polling mode (a letter ID, not @ streaming).
2. Controllers: set MENU → CONTROL → Setpoint Setup → Setpoint Source to Serial/Front Panel. With an analog setpoint source the controller silently ignores serial setpoints (get_device_info warns about this).
3. Find the port: uvx labmcp ports
4. Test the connection:
   bash

   uvx labmcp-alicat --address /dev/ttyUSB0 --check                   # Linux
   uvx labmcp-alicat --address /dev/tty.usbserial-XXXX --check        # macOS
   uvx labmcp-alicat --address COM4 --check                           # Windows
   uvx labmcp-alicat --address COM4 --option unit_id=B --check        # device B on a shared bus
   uvx labmcp-alicat --address tcp://192.168.1.60:4001 --check        # serial-to-Ethernet bridge
   

   Non-default baud rates go in the address: serial://COM4?baudrate=115200.

Add to your MCP client

Claude Code

claude mcp add alicat -- uvx labmcp-alicat --address /dev/ttyUSB0

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

{
  "mcpServers": {
    "alicat": {
      "command": "uvx",
      "args": ["labmcp-alicat", "--address", "/dev/ttyUSB0", "--limit", "max_setpoint=200"]
    }
  }
}

Add --read-only to allow reading flow but block setpoints, gas changes, tares and valve holds (close_valve stays available). For several devices on one bus, add one server entry per unit ID (--option unit_id=A, --option unit_id=B, ...). For other clients, generate the snippet with uvx labmcp config alicat --address /dev/ttyUSB0 --client vscode.

Tools

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

Safety limits

Override at launch, e.g. --limit max_setpoint=500. The default of 100 is deliberately conservative: on a 500 SCCM controller it caps the agent at 100 SCCM until you raise it.

Example prompts

• "What is this controller, what gas is it set to, and what are its units and full scale?"
• "Set the N2 flow to 50 SCCM, log it every 0.5 s for 30 s and tell me how long it took to settle within 1%."
• "Switch the controller to CO2, then ramp the setpoint 0 → 20 → 40 → 60 SCCM, holding each step for 2 minutes, and summarise the mean flow and pressure at each step."
• "The flow reads 0.8 SCCM with the gas off. Close the valve, then tare the flow sensor."
• "Something is wrong with the bioreactor gassing: stop the flow now."

Notes

• Data frame parsing. On connect the server asks the device for its data-frame definition (??D*) and parses every poll against it, so field names, order and engineering units come from the device itself (both the 6v+ column table and the older pre-6v table are understood). If a device does not answer ??D*, frames are parsed by position using the default layouts in the Serial Primer (p. 8) and the manual; layout_source in every reading says which method was used.
• Setpoints use LS on firmware 9v00+ and S on older firmware. After every change the reply is checked: if the controller reports a different requested setpoint (out of range, negative on a unidirectional device, or an analog setpoint source), the tool reports an error with what the device is now using.
• close_valve sets the flow setpoint to 0 (on a flow controller this closes the valve) and then sends HC (hold valves closed, firmware 5v07+), and confirms HLD in the reply. On a pressure controller it only sends HC, because a 0 pressure setpoint can open valves depending on the zero-pressure-control setting (Serial Primer p. 17). resume_control (C) releases the hold; it is marked as a hazard because flow restarts at the current setpoint.
• Tares must be done with no flow. tare_flow and tare_pressure refuse if a flow controller's setpoint is not 0, or if the device still reads more than 2% of full scale. They cannot detect every unsafe situation (e.g. a meter with a small real flow), so still shut the gas off first. Gauge-pressure tares need the port open to atmosphere; absolute tares need the barometer option and an unpressurised line.
• log_flow_series save_path must be a new .csv file: ~ is expanded, missing folders are created, and an existing file is never overwritten. The path is checked before logging starts.
• Gas selection uses GS (10v05+, not saved as the power-up gas unless save_as_power_up) or the older G. Only gases installed on the device are accepted; list_gases shows them.
• Safety guard: a unit ID followed by digits (e.g. A49408) is Alicat's legacy integer setpoint command. The driver refuses to send anything of that shape.
• Meters and gauges silently ignore controller commands; the server refuses controller tools on devices whose data frame has no setpoint.
• Not supported: GP-firmware devices (they need $$ after the unit ID), streaming mode (@), Modbus/Profibus/EtherNet/IP variants, totalizer, batching, PID tuning and COMPOSER mix creation.
• Frame layouts and reply formats were cross-checked against replies captured on real 5v12 to 10v20 devices published by the open-source alicatlib project and the numat/alicat driver.

Hardware verification