press_mechanical — machine_state (current-band)
Physics
Section titled “Physics”A mechanical press’s main drive motor draws current that falls into distinct bands by operating state: near-zero (off, motor de-energized), a steady no-load magnetizing/ friction current while the motor spins but the clutch is disengaged (idle, waiting for the next cycle start or between runs), and a repeating pattern of load peaks riding on top of a running baseline while the press is actively stroking under production (run). A fault state (jam, overload trip, e-stop) typically shows as current dropping to the off/idle band mid-cycle without the expected peak pattern resuming. A split-core CT on one phase of the main motor lead gives a single scalar current signal; the state detector learns the off/idle and run current bands from a rolling window of data (an 8-hour learning window spans multiple shifts and production/non-production periods) and classifies state from which band the RMS envelope sits in, with run additionally confirmed by the per-stroke peak rate from the cycle detector feeding the same signal. Because state changes happen on the order of seconds to minutes (not once per stroke), sampling the rectified current envelope at 10 Hz is more than sufficient to track band transitions in real time while the Nyquist-sensitive per-stroke peak detection is handled by the separate cycle recipe on the same sensor.
Sensor
Section titled “Sensor”- Spec: split-core AC current transformer, clamp-on, 0-100 A range, 1 phase
- Signal: scalar (A), range n/a
Example parts
Section titled “Example parts”- Magnelab SCT-0750-100 split-core CT (100 A, 0-333 mV output)
- YHDC SCT-013-100 split-core CT (100 A, 0-1 V output)
- CR Magnetics CR3110-3100 split-core CT (100 A, 0-5 VAC output)
Mounting
Section titled “Mounting”Clamp the split-core CT around a single phase conductor feeding the press’s main drive motor, inside the motor starter enclosure or at the motor junction box, with the conductor centered in the core and the core fully latched; this can share the same CT already installed for a ct-clamp cycle-count recipe on the same press.
Wiring
Section titled “Wiring”CT output (mV or V AC per the chosen part’s burden resistor) goes to a 2-channel isolated analog input on the edge box’s DAQ module; shield the twisted pair and ground the shield at the DAQ end only to avoid a ground loop with the motor starter enclosure.
Validation
Section titled “Validation”walk the press operator through a scripted off -> idle -> run -> planned stop sequence while an observer logs timestamps, and compare the detector’s state transitions to the logged sequence over the same window
Expected: detector’s state transitions match the logged sequence within +/-10 s per transition once the off/idle and run bands are tuned to the press’s nameplate current
Safety notes
Section titled “Safety notes”- de-energize and lock out the motor starter circuit (LOTO) before opening the enclosure to install the clamp; the enclosure remains live even though the split-core CT itself is non-invasive
- verify the CT’s voltage rating and insulation class match the motor circuit before installing; never install a CT rated below the circuit’s line voltage
- never leave the CT’s secondary open-circuited while current is flowing; keep the burden resistor/DAQ input connected at all times once the clamp is closed
45–180 USD, difficulty 2/5, ~20 min install downtime.