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Fuse test benchRaspberry PLC 19RGPIOControl

Orchestrating PD, non-fusing and fusing test sequences

Automated fuse testing means encoding the standard into software: this example runs the three classic sequences — power dissipation at nominal current, non-fusing at 1.13×In, fusing at 1.45×In — on a Raspberry PLC 19R. Relays select the fuse holder, the loop samples current every 500 ms, and a sample counts as blown when measured current drops below half the setpoint. It is the orchestration layer of a real fuse test bench deployment.

One table, three test types

Each sequence is just a row of parameters: current factor over In, maximum duration, and whether the sample is expected to blow. PD verifies dissipation at 1.00×In, non-fusing demands survival at 1.13×In for an hour, fusing demands melting at 1.45×In. New test types are new rows, not new code.

The 500 ms monitoring loop

Every cycle does two things in strict order: check the safety interlocks, then sample the shunt current. The blown-fuse criterion is robustly simple — measured current under 0.5× the setpoint means the element has melted, since a healthy circuit cannot halve its current with a constant-current source driving it.

Automatic mode from reference files

In automatic mode the operator picks fuse family and rating on the HMI and the setpoints load from reference files — no manual entry, no typos in a certification run. The verdict dict (result, duration, mean current) feeds straight into the TXT report generator.

A snippet from the implementation

Straight from the example as deployed on the Raspberry PLC 19R — copy it freely:

def select_base(base):
    """Energize only the relay of the chosen base (the rest stay open)."""
    for name, relay in BASE_RELAY.items():
        rpiplc.pin_mode(relay, rpiplc.OUTPUT)
        state = rpiplc.HIGH if name == base else rpiplc.LOW
        rpiplc.digital_write(relay, state)
View the full working example Get the full project pack

The full example is a complete program — wiring header, setup and main loop — ready to adapt to your application.

Frequently asked questions

Why is the blown threshold 50% of the setpoint?

A constant-current supply keeps current at the setpoint while the circuit conducts. When the element melts, current collapses toward zero; 50% is far below any normal fluctuation, so the criterion never false-triggers.

How are different fuse holders selected?

Each holder size (10x38, 14x51, 22x58, NH) is wired through its own PLC relay. The sequence energizes exactly one relay before powering up, so the wrong base can never be in circuit.

Can the sequence abort mid-test?

Yes. The interlock check runs before every sample, and any trip — e-stop, microfuse, supply flag — cuts the output and returns an ABORTED verdict with the reason, which lands in the report.

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