injection_moulding — energy (heater-band-power)
Physics
Section titled “Physics”Barrel heater bands are resistive loads driven by a PID-controlled SSR (solid-state relay) per zone, cycling full line current on and off (or phase-angle modulating) to hold a setpoint temperature as the melt pulls heat away. A correctly tuned zone spends a bounded duty fraction energized once at thermal steady state; a failing band element, a stuck-closed SSR, or a degraded thermocouple reading low drives the zone toward a much higher duty cycle or continuous-on, drawing real power well above the learned steady-state baseline for that zone — both an energy-waste signature and an early failure/fire-risk indicator. A CT clamp on each zone’s heater-band circuit, combined with the known line voltage, gives real power per zone. The relevant dynamics are the SSR’s duty-cycle period (typically 1-10 s per PID cycle) and the barrel’s thermal time constant (minutes), not the line waveform itself; sampling at 10 Hz gives >10x margin by Nyquist over even a fast 1 Hz duty-cycle period, resolving the on/off duty pattern cleanly without raw AC waveform capture.
Sensor
Section titled “Sensor”- Spec: split-core AC current transformer, clamp-on, 0-50 A range, 1 phase per zone
- Signal: scalar (kW), range n/a
Example parts
Section titled “Example parts”- CR Magnetics CR3110-3100 split-core CT (100 A, 0-5 VAC output) with a fixed-voltage power calculation in the edge box
- Magnelab SCT-0400-050 split-core CT (50 A, 0-333 mV output), one per heater zone
- ifm electronic EM3350 single-phase power meter (CT + voltage input, 0-10 V kW output)
Mounting
Section titled “Mounting”Clamp one split-core CT around the single-phase conductor feeding each barrel heater-band zone, downstream of that zone’s SSR, inside the barrel heater control cabinet. Centre each conductor in its core, fully latch the core, and label each CT lead with its zone number to avoid cross-wiring zones during data mapping.
Wiring
Section titled “Wiring”Each CT’s output (mV or V AC per the chosen part’s burden resistor) goes to its own channel on a multi-channel analog input module in the edge box; shield each twisted pair and ground the shields at the edge-box end only to avoid a ground loop with the heater control cabinet. Route CT leads away from the SSR’s switched power conductors to avoid switching-noise pickup.
Validation
Section titled “Validation”once the barrel is at steady-state temperature on a stable molding cycle, compare the detector’s learned baseline duty-cycle power for one zone against a handheld clamp meter reading (current x nameplate line voltage) taken on the same zone’s conductor
Expected: detector’s learned baseline within +/-15% of the handheld clamp-meter calculation, and the detector raises an excess-power alarm within 2 learning windows if that zone’s SSR is forced to continuous-on
Safety notes
Section titled “Safety notes”- a qualified/licensed electrician must perform lockout-tagout (LOTO) on the heater control cabinet’s disconnect and verify zero energy with a CAT III (or higher, per the cabinet’s voltage class) rated meter before opening the cabinet to install CTs
- wear arc-flash and thermal-burn rated PPE per the facility’s electrical safety program while the heater cabinet is open; barrel heater zones remain hot long after power is removed, so also allow the barrel to cool or use insulated tools near the bands
- use only a CAT-rated clamp meter matching the cabinet’s voltage class for any live verification after re-energizing
- keep each CT secondary loaded at all times once closed around an energized conductor to avoid a dangerous open-circuit induced voltage
200–700 USD, difficulty 3/5, ~50 min install downtime.