An E-70 brake equipment test rig integrates two completely different fluid power domains — high-pressure hydraulics to 1,040 bar and pneumatics to 10 bar — in a single PLC-controlled platform. The control architecture must manage both safely and without cross-contamination.
The control system architecture separates the two domains at the PLC I/O level. Hydraulic circuit I/O (HP pump control, needle valve position, hydraulic pressure transducers) is assigned to dedicated I/O modules with separate power supply from the pneumatic circuit I/O (pneumatic solenoid valves, low-pressure transducers, dew-point monitor). This electrical separation prevents a wiring fault in either domain from inadvertently commanding the other domain's actuators.
The test sequence manager in the PLC maintains a test state machine. Each COFMOW test type (functional, leakage, endurance, dynamic response) has its own state sequence. The operator selects the component type (distributor valve, brake cylinder, control valve, etc.) and test type from the HMI, and the PLC retrieves the corresponding test parameters from the recipe database — target pressures, ramp rates, hold times, cycle counts, acceptance limits — and executes the sequence automatically.
For leakage testing, the PLC applies test pressure, holds for the specified dwell time while continuously monitoring pressure decay, and calculates leak rate from the pressure decay slope (temperature-compensated). The pass/fail verdict is generated automatically against the component-specific leak rate limit from the recipe database.
For dynamic response testing, the PLC timestamps the command output and the pressure feedback signal that confirms the commanded state has been reached, calculating response time with millisecond resolution using the high-speed I/O timestamps. This requires the pressure transducers to be sampled at high rate (typically 100–500 Hz) during the response measurement phase.
The safety interlock chain runs in a dedicated safety PLC or safety relay system independent of the process PLC — ensuring that the safety functions (auto-locking clamps, emergency stop, pressure relief monitoring) operate even if the process PLC faults. IEC 62061 / ISO 13849-1 PLr d or SIL 2 is typically targeted for the safety functions at this pressure level.
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