daqmon – HP 34970A Data Acquisition Monitor

A Python CLI tool for configuring, scanning, and logging data from the HP/Agilent 34970A Data Acquisition / Switch Unit via serial (RS-232). Readings are logged to the CSV and written to InfluxDB v2.

Installation

pip:

pip install daqmon

uv (installs into the current project or virtual environment):

uv add daqmon

uvx (run without installing — useful for one-off use):

uvx daqmon identify

Quick start

# Create the default config file at ~/.config/daqmon/config.json
daqmon init

# Edit the config to set your serial port and InfluxDB connection
nano ~/.config/daqmon/config.json

# Scaffold a scan definition at ./scan.json
daqmon init-scan

# Identify the instrument
daqmon identify

# Run a scan (Ctrl-C to stop)
daqmon scan myscan.json

# Download the current instrument configuration
daqmon backup -o backup.json

Development

# Clone and install in editable mode with dev dependencies
git clone https://github.com/ameares/daqmon
cd daqmon
uv sync

# Run the CLI from source
uv run daqmon identify

# Lint, format, type-check, test
uv run ruff check src/
uv run ruff format src/
uv run mypy src/
uv run pytest tests/

Files

File	Purpose
config.json	Serial port and InfluxDB connection settings
myscan.json	Scan definition (channels, types, interval)
backup.json	Downloaded instrument configuration (same format as myscan.json)

config.json

{
  "serial": {
    "port": "/dev/ttyUSB0",   // Serial port path
    "baudrate": 9600,          // 9600 default for 34970A
    "timeout": 10.0            // Read timeout in seconds
  },
  "influxdb": {
    "enabled": true,
    "url": "http://localhost:8086",
    "token": "my-token",
    "org": "my-org",
    "bucket": "daqmon",
    "measurement": "hp34970a"
  }
}

Scan definition (myscan.json / backup.json)

Top-level fields

Field	Type	Default	Description
description	string	""	Human-readable label for this scan
scan_interval	float	10.0	Seconds between sweeps
scan_count	int	0	Number of sweeps to run; 0 = infinite (Ctrl-C to stop)
ambient_correction	bool	false	If true, adds a _rise reading for each temperature channel (value minus ambient)
ambient_channel	int	—	Channel number to use as the ambient reference (required when ambient_correction is true)
channels	array	—	List of channel definitions (see below)

Channel fields

Field	Type	Default	Applies to	Description
channel	int	required	all	Channel number: slot × 100 + line (101–120, 201–220, 301–320)
name	string	required	all	Friendly name written as an InfluxDB tag
function	string	"dc_voltage"	all	Measurement function (see table below)
range	string	"auto"	dc_voltage, ac_voltage, dc_current, ac_current, resistance_2w, resistance_4w, frequency, period	Measurement range or "auto"
nplc	float	1.0	dc_voltage, dc_current, resistance_2w, resistance_4w, temperature	Integration time in power-line cycles (0.02–100)
tc_type	string	"K"	temperature, thermocouple	Thermocouple type: J, K, T, E, R, S, B, N
ref_junction	string	"internal"	temperature, thermocouple	Reference junction: internal, fixed, or external
ref_fixed_temp	float	—	temperature, thermocouple	Fixed reference junction temperature in °C (only when ref_junction is "fixed")
ref_channel	int	—	temperature, thermocouple	Channel number of external reference junction (only when ref_junction is "external")
ac_bandwidth	float	—	ac_voltage, ac_current	AC bandwidth filter in Hz: 3, 20, or 200
unit	string	""	all	Unit label written to InfluxDB
gain	float	1.0	all	Multiplier applied to raw reading: result = raw × gain + offset
offset	float	0.0	all	Offset added after gain: result = raw × gain + offset
delay	float	—	all	Relay settling time in seconds inserted after this channel is configured

Supported measurement functions

Key	SCPI function	range	nplc	ac_bandwidth
dc_voltage	VOLT:DC	✓	✓
ac_voltage	VOLT:AC	✓		✓
dc_current	CURR:DC	✓	✓
ac_current	CURR:AC	✓		✓
resistance_2w	RES (2-wire)	✓	✓
resistance_4w	FRES (4-wire)	✓	✓
frequency	FREQ	✓
period	PER	✓
temperature	TEMP (thermocouple)		✓
thermocouple	TEMP (alias)		✓
digital_input	DIG
totalize	TOT

Range values

Function	Valid range strings
dc_voltage	"auto", "0.1", "1", "10", "100", "300"
ac_voltage	"auto", "0.1", "1", "10", "100", "300"
dc_current	"auto", "0.01", "0.1", "1"
ac_current	"auto", "0.01", "0.1", "1"
resistance_2w / resistance_4w	"auto", "100", "1000", "10000", "100000", "1000000", "10000000", "100000000"
frequency / period	"auto", "0.1", "1", "10", "100", "300" (input voltage range)

Example: full-featured scan

{
  "description": "Thermal test – oven channels + power supply",
  "scan_interval": 5.0,          // Sweep every 5 seconds
  "scan_count": 0,               // Run until Ctrl-C
  "ambient_correction": true,    // Add _rise readings for temperature channels
  "ambient_channel": 110,        // Channel 110 is the ambient reference
  "channels": [
    {
      // Thermocouple – internal cold junction reference
      "channel": 101,
      "name": "oven_top",
      "function": "temperature",
      "tc_type": "K",
      "ref_junction": "internal",
      "nplc": 5.0,
      "unit": "degC"
    },
    {
      // Thermocouple – fixed cold junction reference
      "channel": 102,
      "name": "oven_bottom",
      "function": "temperature",
      "tc_type": "K",
      "ref_junction": "fixed",
      "ref_fixed_temp": 23.5,    // Reference junction is 23.5 °C
      "unit": "degC"
    },
    {
      // Thermocouple – external cold junction on another channel
      "channel": 103,
      "name": "sample",
      "function": "temperature",
      "tc_type": "T",
      "ref_junction": "external",
      "ref_channel": 110,        // Cold junction measured on channel 110
      "unit": "degC"
    },
    {
      // Ambient reference channel (used for _rise correction above)
      "channel": 110,
      "name": "ambient",
      "function": "temperature",
      "tc_type": "K",
      "ref_junction": "internal",
      "unit": "degC"
    },
    {
      // DC voltage with explicit range and high integration time
      "channel": 201,
      "name": "psu_output",
      "function": "dc_voltage",
      "range": "10",             // 10 V range
      "nplc": 10.0,              // Slow, high-accuracy
      "unit": "V"
    },
    {
      // DC current with gain/offset scaling
      "channel": 202,
      "name": "load_current",
      "function": "dc_current",
      "range": "auto",
      "nplc": 1.0,
      "gain": 1000.0,            // Convert A → mA
      "offset": 0.0,
      "unit": "mA"
    },
    {
      // AC voltage with bandwidth filter
      "channel": 203,
      "name": "mains_voltage",
      "function": "ac_voltage",
      "range": "300",
      "ac_bandwidth": 20,        // 20 Hz bandwidth filter
      "unit": "Vrms"
    },
    {
      // 4-wire resistance
      "channel": 204,
      "name": "heater_resistance",
      "function": "resistance_4w",
      "range": "auto",
      "nplc": 2.0,
      "unit": "ohm",
      "delay": 0.05              // 50 ms relay settling delay
    },
    {
      // Frequency measurement
      "channel": 205,
      "name": "fan_speed_freq",
      "function": "frequency",
      "range": "auto",
      "unit": "Hz"
    },
    {
      // Digital input (returns integer bitmask)
      "channel": 301,
      "name": "door_switch",
      "function": "digital_input"
    }
  ]
}

CLI reference

daqmon [-c CONFIG] [-v] {scan,backup,identify}

  -c, --config   Path to config.json (default: config.json)
  -v, --verbose  Enable DEBUG logging

  scan SCAN_FILE         Upload config and start scanning
       --poll-interval   Polling rate in seconds (default: 2.0)

  backup [-o OUTPUT]     Download instrument config to JSON (default: backup.json)

  identify               Print *IDN? response

Architecture

cli.py          argparse entry point, signal handling, orchestration
instrument.py   HP34970A SCPI driver over pyserial
config.py       ScanConfig / ChannelConfig dataclasses + JSON I/O
scanner.py      Channel configuration, scan loop, data parsing
influx.py       InfluxDB v2 writer
backup.py       Download instrument config to JSON