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Guide

Machine monitoring without a PLC

Old lathes, presses and CNCs with no network port can still report live. Here are the five ways to get data off a machine without touching a PLC — what each one knows, what it misses and what it takes to fit.

Updated · By Dev Hadvani, Founder of OpeEye

Short answer

You can monitor machines without a PLC in five ways: an operator tablet at the machine, a counter on the cycle-complete signal, a tap on the stack light, a clamp-on current sensor, or a read-only link to the CNC control. The tablet works on any machine and is the only one that records why a machine stopped; the others add hands-free run time and counts. Most floors use a tablet on every machine plus automatic counting on the busiest ones.

The five ways

  1. 01

    Operator tablet

    An Android tablet at the machine. The operator signs in, picks the job and taps pieces, rejects with a reason, and stops with a reason. No wiring; any machine, any age.
  2. 02

    Cycle-complete signal

    A small counting box wired to the signal the machine gives at the end of each cycle (an M-code relay, a door or clamp switch). Exact piece count and run time, hands-free.
  3. 03

    Stack light

    Isolation relays on the green / amber / red tower lamp. Running, idle and alarm states without touching the control. No piece count unless a lamp marks the cycle.
  4. 04

    Clamp-on current sensor

    A current transformer clipped around the power cable. Tells running from idle from off by the current drawn. No piece count, no reasons, no wires cut.
  5. 05

    The CNC control itself

    Read-only, over the network: part count, run state, alarm codes, cycle time and the active program. Needs a control with a supported protocol — OpeEye reads Fanuc, Mitsubishi, Siemens and Haas.

What each method knows

What each way of monitoring a machine without a PLC can record
TabletCycle signalStack lightCurrent clampCNC control
Running / stopped✓✓✓✓✓
Piece countOperator taps✓Rarely—✓
Cycle time—✓——✓
Alarm code——Red only—✓
Why it stopped✓———Alarms only
Why a piece was rejected✓————
WiringNoneOne signalRelays on the lampClip-onNetwork cable
Works onAny machineMost machinesMachines with a tower lampAny powered machineSupported controls

How to pick for each machine

  • Conventional lathe, drill, press, old CNC with no port: tablet; add a cycle-signal counter if counts matter.
  • CNC with a Fanuc, Mitsubishi or Siemens control: connect the control for counts, cycle time and alarms; keep the tablet for reasons and rejects.
  • A machine you are not allowed to touch (warranty, customer-owned): current clamp for run time, tablet for the rest.
  • Injection moulding or a press with a stroke counter: the cycle signal gives exact shots or strokes.

The same choice, with costs and examples, is in tablet vs sensor vs controller monitoring, and how OpeEye does each is on how it works.

Start on the tablet today. Wire later, if it pays.

OpeEye runs every machine on a tablet from the first afternoon, and adds the cycle signal or the Fanuc, Mitsubishi, Siemens and Haas control machine by machine. ₹399 per machine a month either way.

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Questions shop owners ask

Can you monitor a machine that has no PLC?

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Yes. A machine without a PLC or network port can still be monitored five ways: an operator tablet at the machine, a counter on its cycle-complete signal, a tap on its stack light, a clamp-on current sensor on its power cable, or — if it is a CNC — a read-only connection to the control itself. Most floors combine two of them.

Is a CNC controller a PLC?

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Not quite. A CNC control (Fanuc, Mitsubishi, Siemens, Haas) runs the machine's axes and programs, and most have their own way of sharing data — Fanuc FOCAS, MTConnect, OPC UA or the maker's protocol. Reading those gives part counts, run state, alarms and cycle time without touching any PLC logic. OpeEye reads Fanuc, Mitsubishi, Siemens and Haas controls this way.

What is the cheapest way to monitor old machines?

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An operator tablet: any basic Android tablet at the machine, no wiring, and the operator taps pieces, rejects and stops. It works on a 40-year-old lathe as well as a new VMC. With OpeEye the software is ₹399 per machine a month; the tablet is bought locally.

Can a current sensor count pieces?

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Usually not reliably. A clamp-on current sensor sees when the motor draws power, so it tells running from idle and off very well, but a running spindle does not equal a finished piece. For piece counts, use the cycle-complete signal, the controller's part counter or the operator.

Which method tells me why a machine stopped?

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Only a person can, for most stops — waiting for material, no operator, first-piece approval, tool change. Sensors and controllers say that it stopped and for how long; the controller adds alarm codes for breakdowns. That is why the tablet stays even on machines that count themselves.

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