Why is my CMU offline even though it is connected to the Probe?

Why is my CMU offline even though it is connected to the Probe?

A CMU may appear offline in the Dashboard even though it is physically connected to the Probe and its power and data LEDs are on. In some cases the underlying issue is not the CMU itself, but that the Probe did not boot properly and is not reporting connected CMUs. When this happens the required hardware may not be available for selection, which can prevent the experiment from starting.

Normal behaviour: A very brief CMU offline indication of up to about 1 minute is generally not a concern if the CMU returns online and data remains stable.

Note: If the Probe itself is also offline, the CMU being offline is expected — resolve the Probe offline issue first. See: Why is my Probe offline on the Dashboard or not coming back online?

⚠️ Important safety warning

Do not connect or disconnect a CMU while the Probe is powered on.

Doing so is unsafe and may damage the communication or interface circuitry on the Probe or CMU. If this may have happened, stop and contact Pulsenics for further review before continuing.

Agent triage — ask these first

Ask all three before troubleshooting:

1. "Is the Probe itself showing as online on the Dashboard — is the online indicator green?"

   • If unsure: Ask — "Does the Probe's physical blue LED indicator show blue, or does the online indicator in the Dashboard show yellow instead of green?"
   • If still unsure: Continue — resolve any Probe offline state first before investigating the CMU.

2. "Are the CMU power and data LEDs on?"

   • If unsure: Ask — "Can you look at the CMU unit itself — are any small indicator lights visible and on?"
   • If still unsure: Continue — note LED status is unconfirmed and proceed with physical checks.

3. "How are you running the measurement — through the Cloud Dashboard, a local dashboard, or Modbus/scripts?"

   • If unsure: Ask — "Are you clicking buttons on a web page to run the measurement, or is it triggered automatically by a script or PLC?" They can also check by opening dashboard.pulsenics.com — if that's where they run measurements, it's the Cloud Dashboard.

Use the answers to route:

Immediate workaround

The most effective first step in most cases is a controlled power cycle with a proper cable reseat:

1. Power off the Probe
2. Reseat the CMU cable securely at both ends
3. Restart the Probe and allow full startup to complete (up to 5 minutes)
4. Check whether the CMU returns online in the Dashboard with a green indicator

Confirm after: If the CMU comes back online, run 2–3 measurements to confirm it remains stably online before considering the issue resolved.

Physical checks

1. Confirm the RJ45 PoE cable is fully seated at both ends
2. Inspect the cable for damage, strain, or kinking
3. If available, swap in the spare CAT8 PoE-compliant cable included in your Probe Package — do not substitute with other cables
4. Confirm whether the CMU was connected or disconnected while the Probe was powered on — if so, stop and contact Pulsenics before continuing
5. Confirm that the Probe completed startup properly and is reporting connected CMUs in the Dashboard

Network checks — do these if physical checks pass and CMU is still offline

1. Confirm the internet connection is stable
2. Check whether the Dashboard online indicator is yellow instead of green — this indicates the Probe is connecting but not maintaining a stable connection, which can also affect CMU reporting
3. Check signal strength at the Probe setup page (Wi-Fi only):
   • Connect to the Probe's hotspot:
     • Hotspot name: Pulsenics Wifi Setup_PUXXX where PUXXX is your Probe's unit number (e.g. PU198 or PU201)
     • Password: PulseActivate!
   • Open http://setup.pulsenics.com or 1.0.0.1
   • Open the Wi-Fi setup dropdown and note the dBm value
   • General guidance: -50 dBm or better is strong; -50 to -70 dBm is marginal; -70 dBm or worse is weak
4. If Wi-Fi signal is weak or marginal, try Ethernet instead
5. Confirm whether the issue started after a network change
6. If available, test on the Pulsenics-provided InHand IR302 router (black and green square router with antennas) to isolate whether the issue is site-network-specific

Confirm after: After any network change, allow up to 5 minutes and run 2–3 measurements to confirm the CMU remains stably online.

Network-specific consideration

In some cases the CMU connection itself is fine, but weak or incompatible network conditions prevent Probe and CMU status from being reported properly to the server. This can look like:

• Intermittent online and offline status
• Missing channel data
• CMU LEDs on but Dashboard still showing CMU as offline

If the CMU works on the Pulsenics router but not on the client network, site network requirements may need review with the client's IT team and Pulsenics.

Before escalating — collect this information

If the issue continues after physical and network checks, gather the following before contacting Pulsenics:

• Whether the Probe is online or offline
• CMU LED status (power and data LEDs on or off)
• Whether the cable has been reseated and/or swapped with the spare from the Probe Package
• Whether hot-plugging may have occurred
• Number of CMUs affected (one or multiple)
• Connection type (Wi-Fi / Ethernet / company network)
• Signal strength reading in dBm (Wi-Fi only)
• Whether the issue occurs on the Pulsenics router or only on the client network
• Whether this is a first-time deployment or an established setup
• Interface method (Cloud Dashboard / local / Modbus)
• What has already been tried and what effect it had

Prevention

• Never connect or disconnect CMUs while the Probe is powered on
• Use only the CAT8 PoE-compliant cable included in your Probe Package — do not substitute with other cables
• Document site network requirements before deployment
• Use a stable network connection for server communication
• Review network requirements with your IT team when deploying on a client network

Escalate if

Flag for further review if:

• Reseating or replacing the cable does not help
• The CMU stays offline after correct reconnection and restart
• Multiple CMUs are affected simultaneously
• Hot-plugging may have occurred — stop and contact Pulsenics before continuing
• The issue occurs on the client network but not on the Pulsenics-provided router
• The Probe does not appear to have booted properly and is still not reporting any CMUs
• First-time deployment and the CMU has never come online despite passing physical and network checks

What recovery looks like

• CMU appears online in the Dashboard with a green indicator
• CMU data returns and channels report correctly
• Measurement can start normally
• CMU remains stably online across 2–3 consecutive runs

Article status

This is a living troubleshooting note for the symptom CMU offline despite being connected to the Probe. Additional causes, checks, and confirmed resolutions may be added as more cases are identified.

Tags: CMU, offline, Dashboard, cable, PoE, CAT8, hot-plug, network, Probe boot, startup, connectivity, IR302