The short answer
You can measure a CNC machine’s utilisation without touching its control: a clamp-on current sensor on the machine’s supply (or the spindle drive’s supply) shows off, powered-but-idle and cutting as three clearly different current levels. A Shelly EM Gen3 with a 50 A clamp does this for about US$60 a machine and publishes over MQTT. InduQT turns the current into cutting hours, idle hours and stoppages per shift, which is what customers and OEMs mean when they ask a job shop for OEE data.
- Cutting, idle and off hours per machine per shift
- Stoppages longer than a few minutes, with when they started
- Uptime numbers you can show an OEM customer or auditor
- What to buy
- Fit the clamp
- Turn on MQTT
- Set up the MQTT broker (once per plant)
- Check the readings with Claude before you connect anything
- Wire it to InduQT
- What InduQT does with it
What to buy
Two-channel energy meter for clamp-on CTs; Wi-Fi and MQTT. One channel per machine supply, so one meter can watch two machines in the same panel. Maker: Shelly. Maker’s page
Clamps around one phase of the machine’s supply cable. Maker: Shelly. Maker’s page
All three phases of one machine; use it for large machining centres. Maker: Shelly. Maker’s page
Runs the MQTT broker and the InduQT bridge. Any always-on PC or small industrial PC works too. Maker: Raspberry Pi. Maker’s page
Prices are typical street prices in US dollars when we wrote this, not quotes; buy from the maker or a local distributor. InduQT does not sell sensors and is not paid by any maker named here.
Fit the clamp
- Isolate and lock out the machine.
- Clamp the CT around one phase of the machine’s main supply (after the main switch). For spindle-only data, clamp the spindle drive’s supply instead.
- Mount the Shelly EM Gen3 in the cabinet or a small enclosure next to it and power it as in Shelly’s diagram.
- Restore power and run a short program: the device page shows the current rising when the spindle cuts.
Turn on MQTT
- Power the Shelly and join it to the plant Wi-Fi (or plug in Ethernet on Pro models) with the Shelly app, or open its own Wi-Fi hotspot and browse to 192.168.33.1.
- Open the device’s web page (http://<device-ip>) → Settings → MQTT.
- Turn MQTT on. Server: 192.168.1.20:1883 (the Raspberry Pi). User and password: the sensors user.
- Client ID and topic prefix: factory/vmc-01. The bridge reads the machine name from the level after factory/.
- Turn on “Generic status update over MQTT” (status_ntf), so the device publishes its full status to <prefix>/status/<component>:<id> whenever something changes.
- Save and let the device reboot. Within a minute mosquitto_sub on the Pi shows its messages.
The meter publishes factory/vmc-01/status/em1:0 (and em1:1 for its second channel) with current, voltage and act_power. If one Shelly watches two machines, give it the prefix of the first and rename the second channel’s machine in InduQT, or use one meter per machine to keep it simple.
Set up the MQTT broker (once per plant)
The sensors publish their readings to a broker: a small program that receives MQTT messages and hands them to whoever subscribes. Mosquitto is free and runs on a Raspberry Pi, an old PC or a small industrial box on the plant network. You need one per plant, not one per machine. If you already have a broker (Node-RED, Home Assistant, an IoT gateway), use it and skip this step.
# Raspberry Pi OS, Debian or Ubuntu
sudo apt update
sudo apt install -y mosquitto mosquitto-clients
# One user for the sensors and one read-only user for testing
sudo mosquitto_passwd -c /etc/mosquitto/passwd sensors
sudo mosquitto_passwd /etc/mosquitto/passwd viewer# /etc/mosquitto/conf.d/factory.conf
listener 1883
allow_anonymous false
password_file /etc/mosquitto/passwd
acl_file /etc/mosquitto/acl# /etc/mosquitto/acl
user sensors
topic readwrite factory/#
user viewer
topic read factory/## Mosquitto 2 wants these files readable only by its own user
sudo chown mosquitto: /etc/mosquitto/passwd /etc/mosquitto/acl
sudo chmod 0700 /etc/mosquitto/passwd /etc/mosquitto/acl
sudo systemctl restart mosquitto
sudo systemctl enable mosquitto
# Watch everything that arrives (Ctrl+C to stop)
mosquitto_sub -h localhost -u viewer -P 'viewer-password' -t 'factory/#' -vCheck the readings with Claude before you connect anything
Before the data goes anywhere, make sure the sensor is telling the truth. Record two minutes of messages to a file and ask Claude (or ChatGPT) to check them. This catches the usual first-day problems (a clamp on the wrong cable, a probe reading the room instead of the pipe, a sensor that only reports when something changes) while you are still standing at the CNC machine.
# Record 2 minutes of messages to a file you can give Claude or ChatGPT
mosquitto_sub -h 192.168.1.20 -u viewer -P 'viewer-password' \
-t 'factory/#' -v -W 120 | while read -r line; do
echo "$(date -u +%Y-%m-%dT%H:%M:%SZ) $line"
done > sensor-sample.txt# Windows PowerShell, with Mosquitto installed from mosquitto.org
& "C:\Program Files\mosquitto\mosquitto_sub.exe" -h 192.168.1.20 -u viewer -P viewer-password `
-t "factory/#" -v -W 120 | ForEach-Object { "$(Get-Date -Format o) $_" } | Out-File sensor-sample.txtI've attached sensor-sample.txt: two minutes of MQTT messages from a sensor I just fitted to the CNC machine.
Each line is: time, topic, payload.
Please check it for me:
1. List each topic and every numeric field in it, with the min, max and typical value.
2. Tell me whether the values are physically plausible for the CNC machine. I expect three levels: near zero when off, a low steady current when powered and idle (servos, coolant pump, hydraulics), and higher, varying current while cutting. Tell me the three levels you see and how long each lasted.
3. Point out gaps longer than 30 seconds, repeated identical values, or fields that are always 0.
4. Say which fields are worth sending to InduQT as signals and which I can ignore.
Answer in a short table, then a list of anything I should fix before I wire it up.Claude Code or Claude desktop with a terminal can run the mosquitto_sub command for you: ask it to "subscribe to factory/# on 192.168.1.20 as viewer for two minutes and check the readings". Either way the readings stay on your laptop: nothing is stored in InduQT until you wire it up in the next step.
Using a cloud broker (HiveMQ Cloud, EMQX Serverless or your own server with TLS) instead of one on the plant network? Add the free InduQT connector to Claude (https://claude.ai/directory/connectors/induqt) and Claude can listen to the broker for a few seconds itself:
Use InduQT to preview my MQTT broker before I connect it:
url mqtts://<your-cluster>.hivemq.cloud:8883, topic factory/#,
username viewer, password <viewer password>. Listen for 10 seconds.
Then tell me which topic level names the machine and which fields are numeric.Wire it to InduQT
Once the readings look right, send them to InduQT. The simplest way is a small bridge on the same Raspberry Pi: it listens to your broker and forwards every number to InduQT over HTTPS. It works on every InduQT plan, including the free one (up to 3 machines), and nothing on the plant network has to be opened to the internet.
- In Claude with the InduQT connector, paste the prompt below. Claude creates the site, the machine and a key that can only send readings to that site. (No Claude? Do the same in the InduQT app: Add machine with the same externalId, then Settings → API keys → a key with the ingest scope, limited to the site.)
- Copy the key Claude shows you. It is shown once.
- Start the bridge on the Raspberry Pi with that key.
- Ask Claude for the latest values, and set the normal bands.
Set up InduQT for this sensor:
1. Create a site called "Plant 1" (skip if it already exists).
2. Create a machine named "vmc-01" with externalId "vmc-01" and family "cnc".
3. Create an ingest key for the site called "Raspberry Pi bridge" and show it to me once.
After I start the bridge, I'll ask you to check the latest values. The signals will be em1_0.current, em1_0.act_power and em1_0.voltage.python3 -m venv ~/induqt && source ~/induqt/bin/activate
pip install "paho-mqtt>=2.0" requests
export MQTT_HOST=localhost MQTT_USER=viewer MQTT_PASSWORD='viewer-password'
export MQTT_TOPICS='factory/#'
export INDUQT_API_KEY='iq_live_…' # the site key Claude or the app created for you
python3 induqt_bridge.pyinduqt_bridge.py (the whole bridge, about 120 lines)
#!/usr/bin/env python3
"""
induqt_bridge.py — forward MQTT sensor messages to InduQT.
Subscribes to your local broker, turns each message into numbers, and posts them
to the InduQT ingest API in batches. Works on every InduQT plan, including the free one,
and your broker never has to be reachable from the internet.
factory/<machine>/<anything> -> machine = <machine> (matched to the machine's externalId)
factory/pump-3/vibration {"vib_rms_x_g": 0.12} -> signal vib_rms_x_g
factory/comp-1/status/em:0 {"a_current": 12.4} -> signal em_0.a_current
(two or more levels after the machine: the last level names the group, so
two probes or two channels never overwrite each other)
{"temperature": {"tC": 41.2}} -> signal temperature.tC
factory/furnace-1/temp 21.7 -> signal temp (a bare number takes the last level)
pip install "paho-mqtt>=2.0" requests
"""
import json
import os
import re
import threading
import time
import paho.mqtt.client as mqtt
import requests
MQTT_HOST = os.environ.get("MQTT_HOST", "localhost")
MQTT_PORT = int(os.environ.get("MQTT_PORT", "1883"))
MQTT_USER = os.environ.get("MQTT_USER")
MQTT_PASSWORD = os.environ.get("MQTT_PASSWORD")
TOPICS = [t.strip() for t in os.environ.get("MQTT_TOPICS", "factory/#").split(",") if t.strip()]
MACHINE_LEVEL = int(os.environ.get("MACHINE_LEVEL", "1")) # factory/<machine>/... is level 1
SEND_EVERY = float(os.environ.get("SEND_EVERY", "10")) # seconds between posts
IGNORE = set(os.environ.get("IGNORE_FIELDS", "id,ts,time,timestamp,unixtime,Time").split(","))
INGEST_URL = os.environ.get("INDUQT_URL", "https://api.induqt.ai/v1/ingest")
API_KEY = os.environ["INDUQT_API_KEY"] # a site key from InduQT (Settings -> API keys)
BAD = re.compile(r"[^A-Za-z0-9_.\-]")
buffer, lock = [], threading.Lock()
def key(name):
return BAD.sub("_", name)[:64]
def numbers(prefix, value, out):
"""Collect every number in a JSON value; true/false become 1/0."""
if isinstance(value, bool):
out[key(prefix)] = 1 if value else 0
elif isinstance(value, (int, float)):
out[key(prefix)] = value
elif isinstance(value, str):
text = value.strip().lower()
if text in ("on", "true", "online"):
out[key(prefix)] = 1
elif text in ("off", "false", "offline"):
out[key(prefix)] = 0
else:
try:
out[key(prefix)] = float(text)
except ValueError:
pass
elif isinstance(value, dict):
for k, v in value.items():
if k not in IGNORE:
numbers(f"{prefix}.{k}" if prefix else k, v, out)
def on_connect(client, userdata, flags, reason_code, properties):
print(f"MQTT connected ({reason_code}); subscribing to {TOPICS}")
for t in TOPICS:
client.subscribe(t, qos=1)
def on_message(client, userdata, msg):
levels = msg.topic.split("/")
if len(levels) <= MACHINE_LEVEL:
return
machine = levels[MACHINE_LEVEL]
try:
payload = json.loads(msg.payload.decode("utf-8", "replace"))
except ValueError:
payload = msg.payload.decode("utf-8", "replace")
values = {}
group = levels[-1] if len(levels) - MACHINE_LEVEL > 2 else ""
if isinstance(payload, dict):
numbers(group, payload, values)
else:
numbers(levels[-1], payload, values)
if values:
with lock:
buffer.append({"machine": machine, "ts": int(time.time() * 1000), "values": values})
def sender():
while True:
time.sleep(SEND_EVERY)
with lock:
batch = buffer[:500]
if not batch:
continue
try:
r = requests.post(
INGEST_URL,
headers={"Authorization": f"Bearer {API_KEY}"},
json={"readings": batch, "autoCreate": True},
timeout=15,
)
if r.status_code < 300:
with lock:
del buffer[: len(batch)]
print(f"sent {len(batch)} readings: {r.json()}")
elif r.status_code in (400, 401, 403):
print(f"InduQT refused the batch ({r.status_code}): {r.text}")
with lock:
del buffer[: len(batch)] # fix the key or mapping; retrying will not help
else:
print(f"InduQT returned {r.status_code}; will retry")
except requests.RequestException as e:
print(f"network error, will retry: {e}")
with lock:
del buffer[:-5000] # keep at most ~5,000 readings while offline
client = mqtt.Client(mqtt.CallbackAPIVersion.VERSION2, client_id="induqt-bridge")
if MQTT_USER:
client.username_pw_set(MQTT_USER, MQTT_PASSWORD)
client.on_connect = on_connect
client.on_message = on_message
threading.Thread(target=sender, daemon=True).start()
client.connect(MQTT_HOST, MQTT_PORT, keepalive=60)
client.loop_forever()
Keep it running after a reboot (systemd)
# /etc/systemd/system/induqt-bridge.service — keeps the bridge running after a reboot
[Unit]
Description=MQTT to InduQT bridge
After=network-online.target mosquitto.service
[Service]
User=pi
EnvironmentFile=/home/pi/induqt-bridge.env
ExecStart=/home/pi/induqt/bin/python3 /home/pi/induqt_bridge.py
Restart=always
RestartSec=10
[Install]
WantedBy=multi-user.target
# then:
# sudo systemctl daemon-reload && sudo systemctl enable --now induqt-bridge
# journalctl -u induqt-bridge -fThe bridge treats the topic level after factory/ as the machine (it matches the machine's externalId and creates it if needed), turns every number in the message into a signal (nested fields become names like temperature.tC; when the topic has a group after the machine, such as Shelly's status/em:0, the group goes in front, as em_0.a_current, so two channels never overwrite each other; true/false and on/off become 1/0) and sends a batch every 10 seconds. It was run end to end on 2026-10-31 against Mosquitto 2 with Shelly Gen2, Theengs and plain-number messages. Prefer Node-RED? The same bridge as a Node-RED flow is on the gateway guide.
Show me the latest values InduQT has for vmc-01.
Then set these normal bands so InduQT knows what "normal" looks like: em1_0.current between the idle current and the highest cutting current Claude found.On the Plant Monitor plan InduQT can also subscribe to a broker directly. Point your sensors (or a Mosquitto bridge) at a cloud broker with TLS, then ask Claude to "create an MQTT connector for this broker, machine from topic level 1", or add it in the app under the site → Connect data → MQTT broker.
What InduQT does with it
- Learns the off, idle and cutting levels for each machine by itself (operating-regime clustering), so you do not set thresholds machine by machine.
- Reports cutting hours, idle hours and stoppages per shift and per day.
- Flags a machine whose cutting current is creeping up for the same job, an early sign of worn tooling, a dragging axis or a spindle bearing.
- Keeps the history, so you can answer a customer’s “what was your uptime last quarter” in a minute.
In InduQT, for every CNC machine at Plant 1, give me yesterday’s cutting hours, idle hours and the three longest stoppages with start times. Put it in a table I can send to our customer.Frequently asked questions
Is current a good enough proxy for OEE?
For availability (is the machine cutting or not), yes. Performance and quality need cycle counts and scrap counts; add a cycle counter (see the injection moulding guide, the same sensor works on a CNC door or pallet changer) and enter scrap in your MES or a spreadsheet you upload to InduQT.
Can I read the data straight from the FANUC, Siemens or Haas control instead?
Often yes, through MTConnect, OPC UA or FOCAS, but it needs options on the control and someone who knows them. A current clamp works on any machine, old or new, in half an hour.
How much does this cost for 20 machines?
About US$1,200 in meters and clamps plus one gateway, and InduQT’s Fleet Starter plan with 20 machines. Compare that with vendor-sensor systems priced per machine per month: see our Guidewheel alternative comparison.