How to connect a current-sensed machine (no controller needed)
Wiki: Setup, edge and devices
Have a PLC or controller on this machine? Use the regular Connect a Machine flow instead, this page is for a machine with no controller connection at all, where a clamp-on current sensor is the only way to know it’s running.
When to use this
Some machines never had a PLC, or their controller isn’t worth integrating, a bench grinder, a shop vac, an older stamping press, a compressor. You still want to know when it’s running, for how long, and how that rolls into downtime and OEE. Clamp a current sensor around one of its power leads, wire it to the gateway’s analog input, and Spall infers off / idle / running from how much current the machine is drawing, no controller, no extra wiring into the machine itself.
What you need
- A gateway already online (see set up a gateway: from hardware to green).
- A clamp-on current sensor with a voltage output (a CT clamp with an internal burden resistor, not a bare current-loop transducer), clamps around one supply lead to the machine, no rewiring of the machine’s own circuit needed. Ask your Spall contact if you’re not sure which sensor to order.
- One of the gateway’s analog input terminals free, and the sensor wired to it per your Spall contact’s wiring instructions (the physical wiring is a one-time bench/panel task, once it’s landed on a terminal, everything below is done from the app).
Step 1, Start the wizard
Gateways → your gateway → Connect a Machine (or the Connect a Machine button from Getting Started). Pick the gateway, then choose protocol Analog Input (ADC).
Step 2, Mark it as current-sensed
On the Tags step, check “This is a current-sensed machine (no controller)”. A short panel appears:
- Idle threshold / Running threshold, two numbers that separate the three states. Leave the defaults for now. You’ll set real ones in Step 4.
- Current-sense tag id, the name for this derived signal (defaults to
raw_v). You won’t normally need to change it.
Click Set up the current-sense tag + classification. You’ll see a preview of the derived tags about to be created, this is normal. It’s how Spall turns “a clamp on a wire” into a real running/stopped signal, entirely from settings, no file editing. Then, in the tag editor below, set that current-sense tag’s address to the ADC terminal number the sensor is wired to (1, 2, or 3, matching the panel’s AIN1/AIN2/AIN3 terminals).
Step 3, Name and place the machine, then create it
Finish the wizard as usual: name the machine, place it in your site/area/work-center hierarchy, and click Create machine. Push the configuration to the gateway from the confirmation screen.
Step 4, Calibrate against a real cycle
A current-sensed machine’s thresholds start as reasonable guesses, they need one real check before you trust anything built on them. On the machine’s Derived measurements you’ll find two readings worth watching side by side while you run the machine through a real off → idle → running cycle (or off → running, if the machine has no distinct idle mode):
- A state reading that moves through off / idle / running as you cycle the machine, this is the detailed, three-way view.
- A run state reading that’s the simpler on/off summary the rest of the app (downtime, OEE, the wallboard) actually watches, it reads “running” only once the state reading reaches running. Idle and off both read as stopped there, the same as any machine’s run signal.
Watch the state reading climb and fall the way you’d expect as the machine cycles. If it doesn’t match reality at some point, flags idle as running, or never leaves off while the machine is clearly on, go back to the machine’s tags and adjust the idle/running thresholds. Set them roughly halfway between what you observed at each state, not right at the edge of what you saw, so ordinary noise doesn’t flicker the reading between states.
Until you’ve done this, both readings carry a note on their own measurement detail page: “Thresholds set at calibration, verify against a known cycle.” That note is the point, not a warning to dismiss, it’s telling you the classification hasn’t been checked against reality yet.
What you get, and how it’s labeled
Once calibrated, this machine’s run state feeds the exact same downtime detection, OEE, and wallboard tiles every controller-connected machine uses, a current-sensed machine is never a second-class citizen on any of those views. The one difference you’ll always be able to see: its run-state reading (on the machine’s measurement detail page) is labeled “State inferred from power draw”, a note that this state came from a current clamp, not a PLC status bit. That label stays visible for the life of the machine. It’s not a one-time setup note. The detailed off/idle/running state reading stays available on the machine’s measurements for anyone who wants the fuller picture than the plain running/stopped summary the rest of the app uses.
Troubleshooting
- Run state never changes, confirm the sensor is actually wired to the channel number you set in Step 2 (jumper a known signal into that terminal and watch the current-sense level move, the same check described in wiring the gateway’s panel I/O).
- State flickers between idle and running (or off and idle) while the machine holds steady, your thresholds are sitting too close to the machine’s actual current level. Re-run Step 4 and set the boundary further from what you observed.
- “Thresholds set at calibration, verify against a known cycle” never goes away, that note is permanent by design. It’s not a checklist item that disappears. It’s telling you how this machine’s run state was determined, same as any other note in the app.
- You have more current-sensed points than the gateway has analog terminals, see monitor more sensors than your gateway has terminals for aggregating many clamps onto one gateway.