Advanced Solenoid and Valve Control for In Vitro Diagnostic Analyzers

×

Figure 1

   

Abstract

This article highlights the limitations of traditional solenoid and valve control and introduces an integrated solution that leverages advanced current sensing, plunger‑movement detection, and predictive health monitoring for intelligent drive control.

Introduction

In vitro diagnostic (IVD) systems depend on solenoids and valves for precise fluid control, and their performance directly affects diagnostic accuracy. However, traditional drive methods lack feedback and advanced diagnostics, making faults hard to detect. This article will introduce the common failure points of solenoids and valves and explore how the MAX22216 offers a high-performance, integrated solution tailored to meet the demanding requirements of solenoid and valve control in modern IVD equipment.

Solenoids and Valves in IVD Systems

A solenoid is an electromechanical device that converts electrical energy into linear motion by energizing a coil to create a magnetic field, which moves a plunger inside the coil for simple and reliable actuation. In diagnostic instruments, solenoids often actuate valves to regulate the flow of liquids or gases by opening or closing fluid paths. Proportional valves extend this concept by adjusting their degree of opening based on supply current, enabling precise control of flow rates for applications such as reagent mixing or sample preparation.

These components play a critical role in the automation and precision of IVD systems (Figure 1), supporting functions like actuating locks and covers for sample handling, positioning optical shutters during photonic measurements, and ensuring safety interlocks during high-speed operations. Solenoid valves manage fluid routing, reagent delivery, waste handling, and air or gas regulation within complex assay workflows, while proportional valves provide fine control for accurate dispensing and mixing in high-sensitivity tests. Additionally, solenoid-based grippers enable robotic automation by handling tubes, cartridges, and consumables, ensuring seamless sample transfer and sorting. Together, these technologies deliver the high throughput, precision, and safety required for modern diagnostic laboratories while integrating smoothly with advanced robotic systems.

Challenges in Solenoid and Solenoid Valve Control

Large-scale IVD systems often incorporate dozens of solenoids and valves, which can experience several fault conditions (Figure 2) over time including:

• Plunger Stiction or Jamming: Debris, wear, or contamination can cause a plunger to stick or fail to move, leading to incomplete actuation.
• Coil Degradation: Continuous operation and thermal cycling can weaken the coil, reducing magnetic force and causing unreliable motion.
• Electrical Open or Short Circuits: Wiring faults or connector issues can result in open-load or short-circuit conditions, preventing proper energization.
• Valve Wear and Leakage: Mechanical wear or seal degradation can cause valves to leak or fail to close fully, compromising fluid control.
• Silent Failures: Without feedback mechanisms, solenoids may appear to operate normally while failing to move the plunger, leading to undetected errors in fluid handling.

These issues can have serious consequences beyond just technical inconvenience. A faulty valve or solenoid can halt critical fluidic processes, meaning patient samples are not processed on time. This delay slows down the delivery of meaningful diagnostic results that clinicians rely on to make treatment decisions. In high-throughput labs, even a single failure can disrupt workflows, creating backlogs that affect hundreds of tests.

When such faults occur, maintenance technicians often need to troubleshoot the system urgently—sometimes overnight—to restore functionality. In many cases, identifying the exact failing component is difficult, leading to the costly replacement of multiple valves or solenoids as a precaution. This not only increases maintenance expenses but also results in wasted reagents and lost samples, adding to operational costs and impacting patient care.

For these reasons, advanced solenoid control that incorporates fault detection and predictive maintenance is not optional but essential for ensuring system reliability, reducing downtime, and maintaining the integrity of modern diagnostic workflows.

Typical Solenoid Drive Methodology

Solenoids are traditionally operated using a fixed current profile (Figure 3) that includes three distinct phases: excitation, hold, and deactivation. During the excitation phase, a high current is applied for a short duration to generate sufficient magnetic force to move the plunger. This ensures rapid and complete actuation. Once the plunger reaches its end position, the system transitions to a lower hold current, which maintains the plunger’s position with minimal energy. This reduction in current helps to limit heat generation and extend the life of the solenoid. Finally, when the solenoid is deactivated, the magnetic field collapses, and the plunger returns to its default position, typically aided by a spring or gravity.

While this method is widely used, it has several limitations. First, the transition from pull-in to hold current is typically time-based and assumes successful mechanical movement. Second, there is no feedback mechanism to confirm whether the plunger actually moved, which can lead to silent failures. Finally, energy may be wasted if the excitation current is applied unnecessarily long, and the system lacks diagnostic capabilities to detect mechanical faults or wear.

Detection of Plunger Movement

The MAX22216 overcomes solenoid monitoring limitations by using its integrated detection of plunger movement (DPM) feature to verify mechanical actuation without external sensors. By monitoring the coil current during energization, the device detects a characteristic dip caused by back electromotive force (BEMF) when the plunger moves (labeled BEMF Dip in Figure 4), allowing it to distinguish normal operation from a stalled or blocked valve.

The DPM feature operates only on the rising edge of the coil current, using predefined current thresholds DPM_START and DPM_THLD to minimize noise and avoid false detections. When the current exhibits a dip deeper than the DPM_THLD threshold, the IC recognizes this as valid plunger movement and asserts the DPM_STATUS flag. Once the dip event completes, the driver calculates two key timing metrics: REACTION_TIME, which measures the delay between the activation command and the plunger response, and TRAVEL_TIME, which indicates how long the plunger takes to move. If no valid dip is detected, the IC sets a flag to alert the user.

Upon detecting valid plunger movement, the IC can automatically transition from pull-in to hold current (green line in Figure 4), optimizing energy usage and reducing thermal stress. This dynamic adjustment enhances system efficiency and reliability, particularly in high-channel-count diagnostic instruments where solenoids operate continuously.

Figure 5 illustrates how the DPM feature could be used to verify a solenoid valve’s mechanical operation. In a properly working solenoid valve, applying power to the coil generates a magnetic field that pulls the internal plunger from its off position to the on position, allowing liquid to flow through the valve. As the coil is energized, the current initially rises, but when the plunger physically moves, the inductance of the coil changes. This change produces a brief, detectable dip in the current waveform before the current settles to a steady level. The IC monitors this characteristic dip, interprets it as confirmation that the plunger has moved as expected, and therefore confirms normal valve operation without issuing a fault.

In contrast, Figure 5 also shows a faulty solenoid valve in which the coil is energized but the plunger fails to move, due to sticking, blockage, or mechanical wear. Although electrical current still increases when power is applied, the absence of physical plunger movement means the coil’s inductance does not change. As a result, the current waveform rises smoothly to its steady value with no transient dip. Because the IC does not detect the expected current dip associated with plunger motion, it determines that the valve did not actuate correctly and flags a fault condition.

Inductance Measurement

The MAX22216 also includes an inductance measurement feature that goes beyond basic fault detection. By measuring the inductance of the solenoid coil in real time, the device can infer changes in the magnetic circuit caused by the plunger’s position. As the plunger moves within the coil, the effective inductance varies—higher when the plunger is fully inserted and lower when it is partially withdrawn (Figure 6). This relationship provides a sensorless way to estimate relative position without adding external sensors or complex feedback mechanisms.

For proportional valves, where precise control of flow depends on accurate plunger positioning, this capability is particularly valuable. Instead of relying solely on open-loop current control, the system can use inductance data to confirm that the valve opening corresponds to the commanded position. This improves dosing accuracy, reduces calibration complexity, and supports closed-loop control strategies in advanced fluidic systems.

Predictive Valve Health Monitoring

Over the operational lifetime of a solenoid valve, internal components are subject to wear, contamination, and material fatigue. Friction increases, springs may weaken, and deposits can accumulate on the plunger or valve seat. While the valve may continue to actuate, these changes cause the plunger to respond more slowly. This gradual degradation appears electrically as a drift in reaction time and travel time, as illustrated by the trend plot in Figure 7. An increasing reaction time indicates that more time is required for the magnetic force to overcome friction and opposing spring forces, while a longer travel time reflects slower mechanical motion caused by increased resistance or reduced magnetic efficiency.

The key advantage of tracking these parameters is that degradation is detected well before complete failure occurs. Rather than relying on binary open/closed feedback or waiting for a stuck valve, the system observes subtle changes in timing that correlate with aging. By establishing baseline timing values for a healthy valve and monitoring their drift over time, system designers can define maintenance thresholds or trend-based alerts. When reaction or travel times exceed acceptable limits, maintenance can be scheduled proactively during planned downtime.

This approach transforms each solenoid activation into an automatic health check. Monitoring the long-term behavior of reaction time and travel time enables true condition-based maintenance, reducing unexpected failures, improving system availability, and extending the usable life of valves in high duty or mission critical applications.

Additional Diagnostic Features

The MAX22216 integrates a comprehensive set of protection and diagnostic features that can be accessed through its status registers, ensuring robust operation in demanding environments such as large diagnostic instruments. These features fall into two categories: general protections and channel-specific alarms.

General Protections

• Undervoltage Lockout (UVM): Prevents operation when supply voltage drops below a safe threshold, protecting the device and system from unstable conditions.
• Overtemperature Protection (OVT): Monitors internal temperature and shuts down the driver if thermal limits are exceeded, avoiding damage from overheating.
• Communication Error (COMER): Detects faults in the SPI communication link, ensuring reliable data exchange between the driver and the host controller.

Channel Faults and Alarms

• Open-Load Detection (OL): Identifies when a solenoid coil is disconnected or wiring is faulty, preventing wasted actuation attempts.
• Overcurrent Protection (OCP): Trips when current exceeds safe limits, protecting both the solenoid and driver circuitry.
• Hit Current Not Reached Alarm (HHF/CDR): Flags when the commanded pull-in current is not achieved, indicating possible coil degradation or mechanical blockage.
• Resistance/Inductance Alarms (RES/IND): Monitors coil characteristics to detect anomalies such as shorted turns or wiring faults, supporting predictive maintenance.

These protections not only safeguard the hardware but also provide actionable diagnostic data for system-level health monitoring. By leveraging these alarms, designers can implement fault-tolerant architectures that minimize downtime and improve reliability in high-throughput medical devices.

Summary of Benefits for IVD System Designers

As discussed in the beginning of this article, large diagnostic instruments face several challenges when controlling valves and solenoids. Miniaturization demands compact solutions that can manage multiple channels without adding complexity. Heat buildup from long duty cycles accelerates coil deterioration, while stuck plungers or plunger deformation can cause silent failures. Acoustic noise and extended on-off cycles further impact system performance, and without predictive maintenance, wear-related issues often go undetected until failure occurs. Energy efficiency and electromagnetic interference (EMI) are also critical concerns in high-density designs.

The MAX22216 addresses these issues with integrated features that go beyond traditional drivers (Figure 8). It supports up to four channels with built-in current sensing and shunts for space savings. Resistance and impedance measurements help monitor coil health, while the DPM feature verifies actuation and flags errors in real time. Current and voltage ramp control reduce mechanical stress and noise, and fast demagnetization shortens on-off cycles. For predictive maintenance, the device combines impedance monitoring with motion detection to identify early signs of wear. Energy efficiency is improved through two-level current control and automatic transitions from pull-in to hold current, while configurable slope control helps mitigate EMI. These capabilities make the IC a robust, intelligent solution for modern valve manifolds and diagnostic platforms.

Product Summary

The MAX22216 is a highly integrated driver designed for inductive loads such as solenoid valves, proportional valves, DC motors, and relays. It features four programmable 36V half-bridges capable of delivering up to 3.2A per channel, making it suitable for demanding applications in IVD systems. The device supports flexible configurations, including single-ended and bridge-tied loads, with options for voltage or current regulation and mixed control schemes.

Advanced control functions include two-level current sequencing for power savings, ramp control to reduce noise, dither for overcoming static friction, and fast demagnetization for shorter on-off cycles (Table 1). These capabilities improve efficiency and responsiveness in high-throughput environments.

Compact packaging and integrated intelligence make the IC an elegant solution for modern solenoid and valve control, combining performance, reliability, and advanced monitoring in a single device.

Conclusion

The MAX22216 redefines solenoid and valve control for modern IVD systems by combining high-performance actuation with intelligent diagnostics and energy-efficient operation. Its integrated features—such as plunger movement detection, inductance monitoring, and predictive maintenance—help prevent silent failures and reduce downtime. With flexible configurations, advanced protections, and a compact footprint, the IC simplifies design while improving reliability and throughput. For engineers building next-generation diagnostic platforms, it delivers precision, efficiency, and confidence in a single solution.

著者について