press_mechanical — energy (ct-clamp-power)
Physics
Section titled “Physics”Real electrical power P = VIcos(phi) on the press main drive motor feed is the true measure of energized/running load, unlike a bare current reading which cannot tell an idle-but-magnetized motor from a loaded one at low power factor. A 3-phase CT clamp set (one per phase, or two with the third derived) plus a voltage reference tap into a combined power transducer computes true kW continuously. The press’s main contactor can stay closed with the motor spinning unloaded between jobs, drawing idle/no-load real power for hours; that idle band sits well below the stroking-load band, so the detector can flag “energized but not producing” as excess-over-baseline. The dominant waveform energy of interest is the line-frequency power envelope and its slow (seconds-scale) load-transient steps when the press starts/stops stroking, not the stroke events themselves (covered by the count_cycles recipes). Sampling the transducer’s output at 10 Hz resolves a load-step transient that settles over roughly 0.2-1 s (contactor closing, drive ramp) with >5x margin per Nyquist on that transient’s bandwidth, while avoiding the cost of raw-waveform capture needed only for true power-quality analysis.
Sensor
Section titled “Sensor”- Spec: 3-phase power/energy transducer with CT inputs, true-RMS kW output, 0-4 quadrant
- Signal: scalar (kW), range n/a
Example parts
Section titled “Example parts”- ifm electronic EM3350 3-phase power meter (CT + voltage inputs, 0-10 V/4-20 mA analog kW output)
- Veris Industries E50C5 3-phase power transducer (split-core CTs, 0-5 VDC proportional output)
- Continental Control Systems (Accuenergy) WattNode WNC-3Y-208-MB 3-phase power meter (Modbus RTU kW/kWh output)
Mounting
Section titled “Mounting”Clamp one split-core CT around each of the three phase conductors feeding the press’s main drive motor inside the motor starter enclosure, with each conductor centered and the cores fully latched; tap the voltage reference leads from the same enclosure’s line terminals through fused test leads rated for the enclosure’s voltage class. Mount the transducer body on DIN rail inside or immediately adjacent to the enclosure, keeping CT and voltage leads separated from control wiring.
Wiring
Section titled “Wiring”Transducer analog output (0-10 V or 4-20 mA proportional to kW) or Modbus RTU output goes to an analog/serial input on the edge box; for an analog connection, use a shielded twisted pair grounded at the edge-box end only to avoid a ground loop with the motor starter enclosure. Verify the transducer’s voltage input rating matches the press’s supply voltage class before wiring the voltage reference leads.
Validation
Section titled “Validation”command the press to idle (contactor closed, motor energized, no strokes) for 15 minutes and compare the detector’s learned off_kw against a handheld power meter reading taken at the same enclosure terminals
Expected: detector’s learned off_kw within +/-10% of the handheld meter reading, and no excess-energy alarm fires during the idle window
Safety notes
Section titled “Safety notes”- work inside the motor starter enclosure only after a qualified/licensed electrician performs lockout-tagout (LOTO) on the press’s disconnect and verifies zero energy with a CAT III (or higher, per the enclosure’s voltage class) rated meter before any CT or voltage-tap installation
- wear arc-flash rated PPE per the facility’s electrical safety program when the enclosure door is open, even after LOTO, until zero-energy is confirmed
- use only a CAT-rated clamp meter/CT matching or exceeding the circuit’s voltage class for any live verification after re-energizing; never verify with a consumer-grade (CAT I/II) meter on a 3-phase industrial feed
- keep the CT secondary loaded (connected to the transducer input) at all times once closed around an energized conductor; an open-circuited CT secondary can develop a dangerous induced voltage
180–650 USD, difficulty 3/5, ~40 min install downtime.