System-level use cases and risk scenarios

Infusion and syringe pumps cover several clinical patterns: volumetric drip pumps that squeeze a disposable tube, syringe pumps that drive a plunger through a lead screw, and PCA devices that let patients request bolus doses under strict limits. Architectures vary between single-channel and multi-channel workstations, but all share a common need to deliver accurate flow and stop safely when something goes wrong.

Disposable tubing systems tend to emphasize continuous flow, occlusion detection along a long line and strong air-in-line monitoring. Syringe-based mechanisms focus on precise plunger travel, screw backlash and syringe-size identification, because a change in barrel diameter directly changes delivered volume per step. Multi-channel stations often share power and processing while assigning each channel its own actuation, sensing and safety chain.

A typical electronic architecture can be viewed as five cooperating subsystems:

• Motor and actuation: stepper or BLDC drivers translate target flow rates into controlled plunger or roller motion with sufficient torque margin.
• Pressure / occlusion sensing AFEs: low-noise amplifiers and ADCs monitor line pressure to pick up clamps, kinks and downstream occlusion before a dose error becomes severe.
• Bubble / air-in-line detection AFEs: ultrasonic or optical front-ends detect hazardous air volumes and duration in the fluid path.
• Encoder and position sensing: encoder inputs and position sensors track lead-screw rotation, plunger travel and sometimes syringe size.
• Safety interlocks: door and latch switches, syringe presence and anti-free-flow clamps, plus acoustic and visual alarms, enforce safe stop and clear notification when a fault is detected.

Regulatory expectations around dose accuracy, maximum infusion rate, occlusion alarm time and acceptable air burden drive concrete electronic requirements. Motor resolution, screw pitch and encoder feedback set the smallest programmable volume step. Pressure and bubble AFEs must combine sufficient bandwidth and stability to detect real faults without constant nuisance alarms. Safety interlocks and redundancy strategies ensure that no single failure can silently lead to overdose, underdose or uncontrolled free flow.

Stepper / BLDC motor drive and dosing accuracy

The motor drive stage turns infusion setpoints into controlled mechanical motion. Most infusion and syringe pumps use stepper motors to push a lead screw or peristaltic rotor, while higher-end systems adopt BLDC or servo solutions for lower vibration and quieter operation. Motor choice and driver topology directly affect flow smoothness, torque margin and long-term dose accuracy.

Stepper versus BLDC in infusion applications

• Stepper motors offer simple, low-cost position control that maps naturally to volume-per-step when combined with a known screw pitch and syringe size.
• BLDC and servo drives support very smooth motion, low acoustic noise and closed-loop torque or position control, which is attractive for premium bedside and multi-channel pumps.
• The mechanical train, backlash and compliance set hard limits on usable resolution, so motor choice is always evaluated together with the lead screw and syringe mechanics.

Key motor driver IC capabilities

• Micro-stepping and interpolation increase effective position resolution and reduce step-induced pulsation in the flow profile.
• Current regulation and slow / fast decay control determine how consistently the driver delivers torque, which impacts stall margin, temperature rise and acoustic noise.
• Stall and jam detection uses current signatures or back-EMF to flag blocked tubing, end-of-travel events or mechanical jams even before pressure rises fully.
• Diagnostics and protection such as overcurrent, thermal shutdown and open-load detection prevent silent failures that could compromise dose delivery.

From flow setpoint to dose accuracy

Infusion accuracy can be viewed as a chain of conversions. A flow setpoint in millilitres per hour is translated into a step frequency for the motor, which is then divided into micro-steps. Lead screw pitch converts motor rotation into plunger travel, and syringe cross-section converts travel into volume per step. Any loss of steps, excessive mechanical play or unstable current regulation will show up as accumulated volume error over time.

Voltage, current and thermal behaviour

Supply voltage range sets the maximum achievable speed and the ability to maintain torque at higher flow rates. Peak and RMS winding current drive both torque capability and temperature rise in the motor and driver package. Integrated current limiting and thermal protection help keep the system inside safe operating limits without unexpected shutdowns or runaway heating in compact enclosures.

Motor current signatures also complement pressure sensing during occlusion events. A blocked line typically causes a rise in driver current, entry into current limiting or an abrupt stall signature. Cross-checking these motor indicators with pressure AFE data improves confidence in occlusion detection and reduces nuisance alarms from transient load changes or mechanical compliance.

Pressure and occlusion detection AFEs

The pressure sensing front-end turns subtle changes in line pressure into reliable digital information for occlusion and free-flow detection. Infusion systems rely on a range of sensor types, from bridge-based strain and piezoresistive elements to packaged diaphragm modules with analog or digital outputs. Each architecture places different demands on noise performance, offset stability and conversion resolution.

Pressure sensor types and output formats

• Bridge strain / piezoresistive sensors provide low-level differential signals that need instrumentation amplifiers or dedicated bridge AFEs to achieve usable resolution.
• Diaphragm modules with analog outputs combine the sensor and a basic AFE to deliver a ratiometric voltage span such as 0.5–4.5 V over the pressure range.
• Digital pressure sensors integrate ADC and temperature compensation, presenting calibrated pressure readings over I²C or SPI and shifting much of the signal conditioning into the package.

AFE requirements for occlusion thresholds

• Low-noise gain is needed so that small pressure deltas around the baseline remain visible after filtering and digitisation, especially in compliant tubing and low-flow regimes.
• Offset and temperature drift control through calibrated gain, offset trims and periodic zeroing prevents long-term creep from masking occlusion trends or free-flow signatures.
• ADC resolution and sample rate must be sufficient to resolve clinically relevant pressure steps while tracking the slope of a developing occlusion without excessive latency.

Typical pressure signatures and alarm thresholds

During normal infusion the line pressure shows a slow, relatively smooth variation with modest ripple from the actuation mechanism. When the line is kinked or blocked, the average pressure ramps upward with a much steeper slope, reflecting fluid compression and mechanical compliance. Free-flow conditions can present as an unexpected drop or abnormal pattern, where flow continues but pressure no longer tracks the programmed rate.

A dual-threshold strategy is often used. A lower soft limit supports early warning and on-screen prompts using ADC data and digital trend analysis, while a higher hard limit feeds a hardware comparator that asserts an immediate stop and alarm. Separating warning and hard-stop paths allows early intervention without saturating users with nuisance alarms, and still preserves a fast, deterministic safety response if pressure continues to rise unchecked.

Bubble and air-in-line detection AFEs

Air-in-line detection is a critical safety function in infusion systems. Electronics must distinguish truly hazardous air burdens from harmless small bubbles and mechanical disturbances. Two dominant approaches are used: ultrasonic transmission through the tubing wall and optical sensing that monitors how light passes through the fluid column.

Ultrasonic bubble detection chain

• An ultrasonic transducer is coupled to the tubing and driven with periodic bursts at a selected frequency.
• A low-noise receive path with programmable gain and band-pass filtering extracts the useful signal while suppressing low-frequency mechanical noise and high-frequency interference.
• Envelope or peak detection can reduce the waveform to an amplitude or energy metric that tracks how bubbles disturb the acoustic path.

Optical bubble detection chain

• An LED projects light through or along the tubing, and a photodiode collects transmitted or reflected light that depends on the presence of liquid versus air.
• A low-noise transimpedance amplifier converts photodiode current into a voltage signal, with bandwidth chosen to follow bubble passage without amplifying unnecessary noise.
• Optical housings and synchronous detection techniques reduce sensitivity to ambient light, by measuring only during known LED on-times and cancelling slowly varying background levels.

Alarm logic and false-alarm control

Both ultrasonic and optical AFEs ultimately deliver amplitude and timing information that can be interpreted as bubble events. Decision logic typically combines an estimate of event magnitude with its duration and repetition rate to infer approximate air volume, rather than reacting to any single small disturbance. Larger or longer events, or rapidly repeated bursts, map to higher alarm levels and more aggressive actions.

Mechanical shocks, tube handling and pump movement frequently perturb the sensing path. Robust designs suppress these artefacts by ignoring events when the pump is idle, cross-checking with pressure and flow context, and requiring consistent signal patterns over a minimum window before raising a high-priority alarm. The goal is to remain sensitive to clinically relevant air-in-line conditions without creating constant nuisance alerts.

Position sensing, encoders and syringe size detection

Accurate dose delivery depends on knowing how far the actuation mechanism has actually moved and which syringe size is installed. Position feedback from encoders and syringe size sensors turns motor commands into verified displacement, closing the gap between theoretical steps and real delivered volume.

Motor-side position feedback

• Rotary encoders with A/B quadrature and optional index tracks provide incremental or pseudo-absolute position of the motor shaft and screw, enabling missed-step detection and fine dose tracking.
• Hall sensors and index markers deliver simpler pulse-per-revolution or home-position signals, suitable for homing, end-of-travel detection and coarse verification of motor motion.
• Linear encoders or scales directly measure plunger or carriage travel, reducing the influence of mechanical backlash and compliance in high-accuracy syringe pumps.

Syringe size identification mechanisms

• Mechanical detents and switch arrays use cams or notches on the syringe holder to actuate combinations of microswitches, which are read as a code on MCU GPIO pins and mapped to syringe profiles.
• Resistor encoding assigns different divider values to each syringe size, producing distinct voltages for an ADC channel to decode, with optional tolerance windows.
• Linear position sensors infer barrel diameter from the clamp position, using potentiometric or magnetic displacement sensors where mechanical coding is less practical.

Encoder I/O and protection requirements

• Debounced inputs are required for mechanical switches and index lines so that contact bounce does not create spurious size codes or position pulses during loading.
• ESD and surge protection on encoder and sensor lines guards the MCU and AFEs against discharge events and cable disturbances, while default pull-ups or pull-downs define safe states if a wire opens.
• Fail-safe coding ensures that undefined or inconsistent patterns, such as partially actuated switches or out-of-range ADC codes, are treated as unsafe and inhibit infusion.

Dose calculation and safety interlocks depend on these inputs. A mismatched syringe size or unreliable encoder signal can translate directly into over- or under-delivery, so firmware treats invalid or inconsistent readings as reasons to restrict operation, prompt user checks or block infusion until the configuration is verified.

Safety interlocks and fault handling chain

Safety interlocks translate clinical risks into hard rules for when infusion must be inhibited, stopped or allowed to continue under supervision. Hardware and firmware cooperate to monitor doors, clamps, pressures, motion and air-in-line signals, ensuring that no single failure silently compromises patient safety.

Key interlock points

• Door and cassette latching verify that the fluid path and anti-free-flow elements are correctly seated before infusion is enabled.
• Syringe loading and size checks prevent operation with mis-loaded or unknown syringe profiles that would distort dose calculation.
• Anti-free-flow clamp status ensures that gravity-driven flow is blocked whenever the motor is not actively controlling the line.
• Over-pressure and under-pressure conditions indicate occlusion, disconnection or unexpected free-flow, and must map to clear fault responses.
• Air-in-line and motion anomalies use bubble metrics, motor current and encoder data to detect air embolism risk, stalls and uncommanded movement.

IC roles in the safety path

• eFuse and hot-swap devices protect local rails and can cut power to motor drivers or control electronics in severe overcurrent or short conditions, forcing a safe stop.
• Watchdogs and window supervisors monitor MCU activity and timing. If safety-critical tasks stall, run too slowly or misbehave, they trigger resets or transfer control to a safe state.
• Safety MCUs and redundant comparators provide an independent path that watches key signals such as pressure, air-in-line and door switches, and can assert motor-stop and clamp-drive outputs even if the main processor fails.

Fault handling actions

When a fault condition is confirmed, the system executes a defined chain of actions. For high-severity faults this includes an immediate stop of the motor drive, activation of anti-free-flow clamps or valves, and assertion of audible and visual alarms. For lower-level events the response may be limited to warnings and temporary restrictions until the user acknowledges or corrects the condition.

Each event is logged with dose context, timestamps and fault codes so that clinical staff and service teams can reconstruct what happened. Combining multiple detection signals with a structured threat-to-action model helps maintain safe behaviour across overdose, underdose, air embolism and free-flow scenarios, while still avoiding excessive nuisance alarms.

Local power rails and device-level protection

Inside an infusion or syringe pump, the internal power tree conditions battery or adapter input into separate rails for motors, digital logic and sensitive analog front-ends. Local DC/DC converters, eFuses and protection switches ensure controlled start-up, fault containment and clean supplies, independent of the upstream isolated medical power architecture.

Internal rails from battery or adapter input

• Motor rail carries high current and switching noise for stepper or BLDC drivers. It must support inrush and stall currents while avoiding large voltage dips during load transients.
• Logic rail powers the MCU, memory and digital interfaces, typically using one or more bucks to generate 5 V, 3.3 V and core voltages with good efficiency.
• Analog rails supply AFEs, ADCs and references that need low-noise, well-filtered voltages, often implemented as LDO-stabilised rails derived from the main logic supply.

Motor rail control and current limiting

The motor rail experiences the largest and fastest current swings when drivers start, reverse or stall. A current-limited switch or eFuse at the rail input softens inrush into bulk capacitance and wiring, enforcing a predictable current profile during plug-in and start-up. Dedicated motor buck converters then regulate the rail voltage and provide telemetry or fault flags, so that safety logic can respond to overcurrent or thermal events.

Clean analog supplies for AFEs

AFEs for pressure, air-in-line and other sensors benefit from rails that are isolated from motor and digital noise. A common pattern is to derive an intermediate logic rail with a buck converter, then feed one or more LDOs that supply ADCs, amplifiers and reference buffers. Local filtering and careful grounding help prevent motor and switching spikes from corrupting low-level measurements used for alarms and dose calculations.

Device-level protection functions

• Overcurrent and short-circuit protection in eFuses and DC/DC converters limits rail current, clamps fault energy and prevents wiring or PCB traces from overheating under fault conditions.
• Overtemperature protection shuts down or derates PMICs and motor drivers before device temperatures exceed safe limits, supporting thermal design margins in compact housings.
• Reverse-polarity protection prevents damage if an external adapter or battery pack is connected with reversed polarity, often using ideal-diode controllers or reverse-blocking FETs.
• Brown-out and undervoltage monitoring on logic rails ensures that the MCU and memory operate within specified ranges and trigger controlled resets when supply margins are lost.

Local protection devices also form part of the safety chain. For severe faults such as persistent motor overcurrent, internal short circuits or runaway motion, safety logic can command eFuses or power switches to cut off the motor rail entirely, removing energy from the faulted path. This complements normal firmware controls and links power integrity directly to patient safety.

MCU, user interface and communications

The MCU or SoC is the control centre of the infusion pump, coordinating closed-loop dosing, safety checks, user interaction and data logging. Around it, interface devices and communication links connect the pump to operators, hospital systems and service tools, while safety-conscious firmware schedules time-critical tasks and alarms.

Control, safety and logging responsibilities

• Closed-loop dosing control reads encoder, pressure and bubble data, compares them against the programmed therapy, and adjusts motor speed and direction to track the target flow.
• Alarm and safety logic evaluates thresholds and state machines across all safety inputs, deciding when to warn, when to stop, and when to command hardware cut-offs or clamps.
• Event logging records dose history, alarms, configuration changes and service data in non-volatile memory to support clinical traceability and troubleshooting.

UI handling and processing architecture

The same controller usually drives the operator interface, including keypad or touch input, display updates and audible indicators. In simpler pumps this may run on a single-core MCU with bare-metal code or a lightweight RTOS, using priority schemes to ensure that safety and dosing tasks always pre-empt UI rendering work. In more complex or multi-channel designs a dual-core SoC or companion safety MCU separates real-time control from rich UI tasks to prevent interface load from delaying safety loops.

Communication interfaces to external systems

• Serial links such as UART or RS-485 connect to local hubs, external control panels or service fixtures for configuration and diagnostics.
• Fieldbus and network interfaces including CAN, Ethernet or proprietary hospital networks allow integration into central monitoring and infusion management systems.
• Wireless options such as Wi-Fi or Bluetooth Low Energy are often provided through dedicated modules, extending connectivity for fleet management or remote updates while leaving security details to higher level system design.

Together, the MCU, UI hardware and communication channels determine how safely and transparently the pump interacts with staff and infrastructure. Control loops and safety functions remain prioritised, while interface and network features add usability and integration without diluting core protection measures.

Design checklist and IC role mapping

This section condenses the infusion and syringe pump architecture into a practical design checklist and IC role map. Engineers can work through the items during concept definition, schematic review and safety analysis to confirm that motion control, sensing, safety interlocks and power protection are all covered by appropriate device choices and diagnostics.

Motor and drive selection checklist

• Run and stall current ranges, including worst-case viscosity and back-pressure, are quantified and matched to driver capability and thermal limits.
• Supply voltage range and margins account for low battery conditions, cable drops and motor back-EMF under fast deceleration.
• Micro-step resolution, screw pitch and gear ratios are mapped to the minimum commanded dose and flow accuracy requirements.
• Current chopping scheme and motor noise spectrum are reviewed against AFE bandwidths and EMC limits.
• Stall detection, overcurrent and thermal protection responses are defined and linked into safety interlock logic, not left as default device behaviour.

Pressure, bubble and position sensing checklist

• Pressure sensor type, range and overload capability are chosen for the full combination of tubing, patient position, head height and fluid properties.
• ADC resolution, noise and sampling rate provide sufficient granularity around occlusion thresholds and early rise detection.
• Bubble detection scheme (ultrasound or optical) and AFE gain settings are tied to minimum detectable bubble volume and maximum acceptable false alarm rate.
• Position feedback resolution from encoder or linear scale is translated into mL per count and verified against clinical dose accuracy.
• Syringe size detection method defines safe behaviour for unknown, inconsistent or out-of-range codes, including interlock and alarm policies.

Safety interlocks and fault response checklist

• Door, cassette latch, clamp position, over-pressure and air-in-line all have clearly defined fault levels, allowed delays and alarm categories.
• Inputs that require hardware redundancy, such as door and clamp status or critical pressure thresholds, have a comparator or safety MCU path independent of the main MCU.
• Events that can be handled in software only, such as low battery or log capacity, still include time-to-alarm requirements and safe fallback modes.
• For each interlock, the system defines whether the pump must stop immediately, block new infusions or operate under restricted conditions.
• Hardware cut-off paths such as eFuses and load switches are associated with specific hazards to ensure that removal of energy is possible when firmware is not sufficient.

Power and protection checklist

• Battery endurance is calculated for typical and worst-case scenarios, including maximum flow, dual-channel operation and extended alarm activity.
• A full power budget covers motor, control, UI and communication loads, with thermal evaluation in the intended enclosure and ambient conditions.
• Peak current during motor start-up, stall and simultaneous channel activity is compatible with adapter, battery and eFuse or hot-swap limits.
• Reverse-polarity, short-circuit and overvoltage conditions at the input are handled by clearly designated protection devices, with defined interaction with the safety chain.
• Logic rails have brown-out supervision to guarantee clean reset and deterministic behaviour when supply margins are lost.

IC role mapping across the pump electronics

Together, the checklist and role mapping help align device choices with safety and performance goals, ensuring that each clinical risk has a corresponding sensing path, protection element and control decision.

Mini design stories and example IC stacks

The following mini design stories show how the building blocks of an infusion or syringe pump can be combined into realistic architectures. Each example highlights constraints, preferred topologies and an indicative IC stack with concrete part numbers, giving a starting point for detailed design and vendor comparison.

Use case 1: single-channel bedside pump with 12 V adapter and battery backup

A single-channel bedside pump is often powered from a 12 V wall adapter with an internal battery that keeps therapy running during short mains interruptions. Motor power is moderate, mechanical noise must be controlled for a quiet ward, and the cost structure allows robust drivers and AFEs as long as the overall bill of materials remains reasonable.

A typical architecture routes the 12 V input and battery through an OR-ing stage and eFuse or hot-swap controller, then into separate buck converters for the motor rail, logic rail and auxiliary rails. The stepper driver controls a lead screw, while a bridge-based pressure sensor with instrumentation amplifier and ΣΔ ADC monitors occlusion. Optical air-in-line detection uses an LED, photodiode and TIA with comparator thresholds. A mid-range MCU runs dosing control, alarm logic, UI and local logging, while UART or USB connects to bedside or nurse station equipment.

Example IC stack (indicative part numbers)

• Motor driver: stepper driver such as DRV8880 or DRV8881 for micro-stepping, adjustable current regulation and integrated protection.
• Pressure sensing AFE: instrumentation amplifier AD8421 feeding a 24-bit ΣΔ ADC such as AD7124-4 for precise occlusion thresholds and drift performance.
• Optical bubble detection: low-noise TIA such as ADA4528-1 or OPA380 combined with a fast comparator like TLV3501 for threshold detection on photodiode current.
• Power protection: eFuse or hot-swap controller such as TPS25942A or LTC4365 for inrush control, overcurrent limiting and reverse protection on the 12 V input.
• Supervision and watchdog: voltage supervisor and watchdog such as TPS3852 or ADM8323 to enforce brown-out reset and MCU activity checks.
• MCU: Cortex-M4 microcontroller in the STM32L4 or Kinetis K32L family with integrated ADCs, communication interfaces and sufficient flash for UI and logging.

Use case 2: PCA syringe pump with compact battery and ultra-low power

A patient-controlled analgesia syringe pump relies on a compact battery pack and must run quietly, often close to the patient. Average power consumption is tightly constrained by long mission times and standby periods, while safety functions and logging still require continuous attention to sensors and user inputs.

The power tree is commonly built around a high-efficiency buck-boost PMIC that supports both active drive and deep-sleep states, with minimal quiescent current. A low-current stepper driver or H-bridge controls the syringe plunger. Pressure sensing may use a digital-output medical-grade pressure transducer to reduce analog overhead, while air-in-line detection can be implemented with a small ultrasound AFE or highly integrated optical module. An ultra-low power MCU with deep-sleep modes, RTC and low-leakage GPIO manages dosing, UI, logging and communication, often with a BLE module for configuration and maintenance.

Example IC stack (indicative part numbers)

• PMIC: ultra-low I_Q buck-boost converter such as TPS63070 or LTC3531 to supply logic and motor rails from a single-cell Li-ion battery.
• Low-power motor driver: stepper or brushed driver such as DRV8834 or A3901, optimised for reduced current and compact packages.
• Digital pressure sensor: integrated transducer like the NXP MPX series with I²C output or TE Connectivity MS4525 family to simplify analog design.
• Ultrasound or optical AFE: low-power ultrasound-front-end such as ADI ADuCM350 class device, or a compact optical AFE combining LED drive and TIA.
• Watchdog and supervisor: nano-power watchdog such as TPS3436 or MAX16056 monitoring the MCU and ensuring recovery from software hangs.
• MCU and wireless: ultra-low power MCU from the STM32L0 or EFM32 Tiny Gecko family together with a BLE SoC module such as nRF52832 for configuration and short-range telemetry.

Use case 3: multi-channel infusion workstation module

A multi-channel infusion workstation hosts several pump channels on a common power and communication backplane. Each channel has its own motor, AFEs and interlocks so that a failure in one path does not compromise others. Shared infrastructure for power conversion and communication reduces cost per channel, but thermal density and rail protection become more critical.

A typical design starts from a 24 V backplane input managed by a hot-swap controller and multi-output digital power system with PMBus for configuration and monitoring. Each channel uses an individual stepper driver, local current sensing and a companion pressure and bubble AFE. Control may be distributed, with a small MCU per channel and a higher-level supervisor MCU managing the user interface and workstation-level safety logic. Communication with hospital systems uses CAN or Ethernet, while a separate safety MCU monitors rails, temperatures and interlock summary signals.

Example IC stack (indicative part numbers)

• Backplane hot-swap and eFuse: devices such as LTC4260 or TPS25982 managing inrush, fault isolation and telemetry on the 24 V input.
• Digital power and PMBus controller: multi-rail supervisors such as LTC2975 or UCD9090 providing sequencing, voltage monitoring and fault logging.
• Per-channel motor drivers: stepper drivers like TMC2130 or DRV8825 for each pump channel, offering micro-stepping and integrated diagnostics.
• Per-channel AFEs: 16-bit or 24-bit ADC such as ADS131E04 combined with MUX switches to serve pressure and bubble detection circuits per channel.
• Channel MCUs: compact Cortex-M0+ devices such as STM32G031 or LPC11Uxx providing local control, with a higher-performance MCU such as STM32F4 managing the workstation UI.
• Communication and safety: CAN transceivers (for example, TCAN1042) or Ethernet PHYs, plus a safety MCU that aggregates interlock and rail status and commands global shut-down when required.

Frequently asked questions about infusion and syringe pump design

Infusion pump FAQ data structure – key design targets at a glance

• Flow accuracy: design for composite infusion rate error around ±5 % or better over the specified operating range, accounting for mechanics, motor control and sensing.
• Position resolution: ensure several encoder or step counts per minimum bolus or smallest rate increment, with cumulative error bounded over the longest infusion time.
• Pressure detection: choose AFE and ADC so occlusion trends are visible as a gradual rise above baseline; implement soft and hard thresholds with time-over-threshold filtering to distinguish true occlusions from transient events.
• Bubble detection: dimension ultrasound or optical AFEs for the smallest clinically relevant bubble volumes in the chosen tubing, while limiting false alarms due to motion, foam and ambient light changes.
• Hardware safety paths: map door, clamp, overpressure, air-in-line and motor overcurrent into comparator, watchdog and power-switch circuits that can stop the pump even if firmware becomes unresponsive.
• Power behaviour: provide seamless switchover between mains and battery within allowed voltage windows, and define clear rules for alarm, continuation or controlled stop when remaining capacity drops below the safe margin for the current therapy.
• Diagnostics and logging: design for detection of single-point failures on critical sensors and rails, and store time-stamped events, settings and fault codes over a multi-day window to support post-event analysis and field debugging.