APF195 204-195-000-021 is a high-performance DC-DC power converter from the Meggitt Vibro-Meter product line, specifically designed for 24 VDC power supply requirements in industrial applications, particularly for machinery condition monitoring systems. This module converts an input DC voltage (9.4 to 36.0 VDC) into two stabilized 24 VDC outputs, each capable of delivering 0.13 A. When higher output current is required, the two outputs can be connected in parallel to achieve a maximum output of 0.26 A / 6.2 W.
The core of the APF195 is based on the 20 IMX 7-24-24-9 7 Watt DC-DC converter manufactured by Power-One Ltd. This converter utilizes a current-mode PWM (Pulse Width Modulation) flyback topology, offering high efficiency, a wide input range, electrical isolation, and excellent dynamic response characteristics. The converter itself is mounted on a DIN mounting support (corresponding to Power-One's Basic Kit DMB IMX/S 7) and is protected by a transparent plastic cover, forming the complete APF195 module.
As a supporting power supply component for the Vibro-Meter VM 600 series rack systems, the APF195 is typically installed on a DIN rail within the control cabinet housing the rack(s). It is used to provide stable ±24 VDC or 24 VDC operating power to external hardware located outside the rack, such as GSI-type galvanic isolation units. Its DIN rail mounting method simplifies system integration and expansion.
204-195-000-021 is the current mainstream ordering number for the APF195, superseding the earlier 011 version. Compared to the 011 version, the 021 version maintains full compatibility in electrical performance and mechanical interface, while potentially incorporating optimizations in manufacturing processes, component selection, or certification updates, ensuring long-term supply stability and reliability. This model is widely used in vibration monitoring systems across power generation, petrochemical, metallurgy, rail transportation, and other industries, making it an ideal choice for both new projects and existing system maintenance.
II. Key Features and Benefits
1. Wide Input Voltage Range and High Reliability
Wide Input Voltage Range (9.4 to 36.0 VDC): Adaptable to various DC power environments such as 12V, 24V battery systems or rectified power supplies, maintaining stable output even with input voltage fluctuations.
High Reliability Design: Based on the mature platform of the Power-One IMX 7 series, featuring integrated planar magnetics and automated surface-mount technology with no internal wire connections, greatly enhancing reliability and consistency.
High Efficiency (Typical >80%): Reduces power dissipation and temperature rise, prolonging service life and minimizing thermal impact on other equipment within the control cabinet.
High MTBF: According to MIL-HDBK-217F standards, under ground fixed conditions at 40°C, the MTBF can exceed 248,000 hours, suitable for long-term continuous operation.
2. Dual Isolated Outputs and Flexible Configuration
Two 24 VDC Outputs: Each can independently supply 0.13 A, allowing independent powering of two devices requiring 24 V supply.
Electrically Isolated Outputs: Electrical isolation is provided between the two outputs as well as between input and output (input/output isolation voltage 1.5 kVDC), enhancing system safety and allowing flexible output configurations (series connection or symmetrical ± supply).
Parallel Connection Capability: The two outputs can be directly connected in parallel (no external diodes required), providing a maximum total output current of 0.26 A / 6.2 W to meet the needs of higher power devices.
Flexible Load Distribution: Dual output units support flexible load distribution, allowing users to freely allocate power between the two outputs based on actual load conditions.
3. Comprehensive Protection Functions
Output Short-Circuit Protection (Hiccup Mode): When an output short circuit occurs, the converter immediately shuts down and attempts to restart periodically (typical frequency 16.5 Hz, pulse width 8.5 ms). Once the short circuit fault is cleared, the converter automatically resumes normal operation without manual intervention.
Output Overvoltage Protection: Output voltage is limited by Zener diodes to prevent damage to downstream loads caused by abnormally high output voltage due to internal faults. Note that this protection is not designed to withstand externally applied overvoltages.
Input Transient and Reverse Polarity Protection: Built-in input transient suppression circuitry. The 20 IMX 7 type features overvoltage lockout (shutdown at approx. 38 V), protecting the input up to 50 VDC. In case of input reverse polarity, the internal diode conducts; external fast-acting fuse (F2A recommended) effectively protects the internal circuit.
Input Inrush Current Limitation: The very low input capacitance design keeps inrush current low and can be further limited by an external series resistor.
4. Industrial-Grade Environmental Adaptability
Wide Operating Temperature Range (-40 to 85°C): Stable operation in harsh industrial environments without derating, suitable for outdoor cabinets or non-temperature-controlled environments.
Vibration and Shock Resistance: Compliant with IEC 60068-2-6 (vibration) and IEC 60068-2-27 (shock) standards, suitable for applications subject to vibration such as transportation, rail, and industrial machinery.
Damp Heat Resistance: Passes IEC 60068-2-3 (damp heat steady state) testing, reliable operation in high-humidity environments.
No Derating Design: No derating required across the entire operating temperature range, simplifying system design.
5. Standard DIN Rail Mounting and Compact Design
TH 35 Standard DIN Rail Mounting: Compliant with EN 50022 / IEC 60715, facilitating quick installation and integration within control cabinets.
Compact Dimensions (50 × 72 × 97 mm): Occupies minimal space, suitable for space-constrained control cabinets.
Transparent Protective Cover: Protects the internal converter and wiring while allowing observation of status indicators (if present).
6. International Safety Certifications
Compliant with IEC/EN 60950 and UL 1950: Meets safety standards for information technology equipment, providing supplementary insulation and SELV outputs.
UL and CSA Certification: UL 1950 and CAN/CSA C22.2 No.950-95 certified for the North American market.
CE Marking: Compliant with EU Low Voltage Directive and EMC Directive requirements.
EAC Certification: Compliant with Eurasian Customs Union technical regulations TR CU 004/2011 and TR CU 020/2011.
7. Electromagnetic Compatibility (EMC)
Low Conducted and Radiated Emissions: Compliant with EN 55022 Class B requirements, suitable for most industrial environments without requiring additional filters.
High Immunity: Compliant with IEC/EN 61000-4-2, -3, -4, -5, -6 standards, exhibiting excellent suppression capabilities against electrostatic discharge, radio-frequency electromagnetic fields, electrical fast transients/bursts, surges, and conducted disturbances.
External Filter Options: For more demanding applications (e.g., IEC/EN 61000-4-5 Level 2), external inductors and capacitors can be added for enhanced protection.
III. Typical Applications
Leveraging its wide input range, dual isolated outputs, high reliability, and DIN rail mounting, the APF195 204-195-000-021 is primarily used in the following scenarios:
VM600 Series Rack System Companion Power Supply: Provides ±24 VDC or 24 VDC operating power to external GSI-type galvanic isolation units (e.g., GS112x series) located outside the rack. This is the core application for the APF195.
Machinery Condition Monitoring Systems: Supplies stable 24 V auxiliary power to sensor signal conditioners, data acquisition units, remote I/O modules, etc.
Industrial Automation and Control Cabinets: Centralized power supply for 24 V devices such as PLCs, interface converters, relay modules, and indicators.
Power Generation and Transmission/Distribution Facilities: Provides reliable power for vibration monitoring systems, partial discharge monitoring equipment, etc., in power plants and substations.
Petrochemical and Oil & Gas Facilities: Serves as the pre-stage power supply for intrinsically safe power supplies powering monitoring equipment in hazardous areas (via safety barriers).
Rail Transportation and Onboard Equipment: Suitable for mobile applications powered by batteries or subject to significant voltage fluctuations, such as rolling stock vibration monitoring systems.
Marine and Offshore Engineering: Provides stable power for shipboard monitoring systems, meeting stringent environmental requirements.
Legacy System Maintenance and Spare Parts: Serves as a replacement for early 011 versions, ensuring system consistency.
IV. Core Technology and Functional Details
1. High-Efficiency Platform Based on Power-One IMX 7 Series
The core of the APF195 is the 20 IMX 7-24-24-9 7 Watt DC-DC converter manufactured by Power-One Ltd. The IMX 7 series is a high-reliability power module family designed for industrial and transportation applications, featuring the following technical characteristics:
1.1 Current-Mode PWM Flyback Topology
Employing a current-mode PWM (Pulse Width Modulation) controlled flyback topology offers several advantages:
Fast Dynamic Response: Quickly responds to input voltage and load variations, minimizing output voltage fluctuation.
Cycle-by-Cycle Current Limiting: Built-in cycle-by-cycle current limiting effectively protects power switches and the transformer.
Simplified Loop Compensation: Current-mode control simplifies feedback loop design and enhances stability.
1.2 Integrated Planar Magnetics
The IMX 7 series utilizes integrated planar transformers and inductors, offering benefits over traditional wound magnetics:
High Consistency and Repeatability: Automated production ensures consistent performance across modules.
Low Leakage Inductance and Low EMI: Planar structure reduces leakage inductance and parasitic parameters, lowering EMI.
Compact Size: Planar magnetics enable a smaller overall footprint and higher power density.
1.3 Magnetic Feedback Technology
For dual output units (such as the 20 IMX 7-24-24-9), the output voltage is monitored via a separate transformer winding located close to the secondary windings and fed back to the primary-side control circuit through a pulse transformer. This magnetic feedback technique offers advantages over optocoupler feedback:
Higher Reliability: Eliminates the optocoupler, avoiding issues related to aging, temperature drift, and lifespan.
Superior Isolation Performance: The pulse transformer provides inherent electrical isolation without requiring additional isolation components.
Wide Temperature Range: Magnetic feedback remains stable across the entire operating temperature range.
1.4 High-Efficiency Design
The IMX 7 series maintains high efficiency (typically >80%) across the entire input voltage range, achieved through:
Low-Loss Power Switches: Utilizes MOSFETs with low on-resistance RDS(on)RDS(on).
Optimized Transformer Design: Minimizes core losses and copper losses.
Synchronous Rectification (in some models): Although not explicitly stated for the 20 IMX 7-24-24-9, overall efficiency remains at a high level.
2. Output Paralleling and Flexible Configuration
One of the most notable features of the APF195 is that its two outputs can be directly paralleled without requiring external current-sharing resistors or diodes. This is enabled by the internal design of the IMX 7 series:
2.1 Principle of Parallel Operation
When the two outputs are paralleled, the converter's current limiting circuit (primary-side controlled) limits the total output power to approximately 7 W. Since both output voltages are regulated to the same value (24 V), they automatically share the load current. In practice, the total output current after paralleling can reach 0.26 A, with a total power of 6.2 W, approaching the converter's maximum output capability.
2.2 Parallel Application Notes
No External Diodes Required: While paralleling does not require external diodes, if redundancy or reverse current blocking is needed, Schottky diodes could be series-connected in each output positive lead. However, this voltage drop and power dissipation. In standard APF195 applications, this is typically unnecessary.
Start-up Behavior: The start-up current after paralleling may be slightly higher than for a single output, but the converter's soft-start function ensures a smooth start.
Current Sharing: Due to internal parameter variations, the current distribution between the two outputs may not be perfectly equal, but the design ensures the difference is within acceptable limits for most applications.
2.3 Flexible Load Distribution
For dual output units, the IMX 7 series supports flexible load distribution, meaning one output can vary from 0% to 150% of its nominal power while the other output continues to operate normally (as long as the total power does not exceed 7 W). This means one output of the APF195 can be briefly overloaded (e.g., 0.2 A) while the other is lightly loaded, as long as the total power remains below 6.2 W. This characteristic provides convenience when dealing with asymmetrical loads.
3. Detailed Protection Mechanisms
3.1 Input Transient and Reverse Polarity Protection
The 20 IMX 7 type incorporates a built-in overvoltage lockout circuit. When the input voltage exceeds approximately 38 V, the converter automatically shuts down, protecting internal circuits from excessive voltage damage. The input can withstand voltages up to 50 VDC without damage.
For higher transient voltages (e.g., the ±2 kV surge required by IEC/EN 61000-4-5 Level 2), it is recommended to add an external filter circuit at the input, including an inductor and a capacitor, as shown in Figure 1. For the 20 IMX 7 type, a transient suppression diode (e.g., Motorola 1.5KE39A) connected in parallel with the input is also required.
Input Reverse Polarity Protection: When the input voltage is reversed, the internal suppression diode conducts forward, generating a large current. An external fast-acting fuse (F2A recommended) must be used in conjunction, causing the fuse to blow and thus protecting the converter. Without the fuse, reverse polarity could damage the converter.
3.2 Output Short-Circuit Protection (Hiccup Mode)
The APF195's output short-circuit protection employs "Hiccup Mode." When an output short circuit is detected, the converter immediately shuts down the output, waits for approximately 60 ms, and then attempts to restart. If the short circuit persists, it shuts down again and repeats this cycle (typical frequency 16.5 Hz, pulse width 8.5 ms). The average short-circuit current in this mode is very low (far below the rated current), thus causing no thermal stress to the converter. Once the short circuit fault is cleared, the converter will resume normal operation during the next restart cycle, with the output voltage rising smoothly without overshoot.
3.3 Output Overvoltage Protection
Both outputs of the APF195 are protected against overvoltage by Zener diodes. For dual output units, the protection diode is typically connected only across the second output. However, because the two outputs track each other (via transformer coupling), if the output voltage on either output rises abnormally, the protection diode will activate. Its operating principle is: if the feedback control loop fails, causing the output voltage to rise above the Zener diode's breakdown voltage, the diode will break down and enter a short-circuit state, thereby clamping the output voltage to a safe level. The primary purpose of this protection is to prevent overvoltage caused by a converter internal fault, not to withstand externally applied overvoltages.
3.4 Inhibit Function
The inhibit input (pin 3) of the APF195 allows remote control of the output(s) via an external logic signal. This function is active low:
When pin 3 is connected to Vi- (input negative) or a low logic level (0 to 0.8 V) is applied, the output is enabled (normal operation).
When pin 3 is left open or a high logic level (2.4 V up to the input voltage) is applied, the output is inhibited (disabled).
If the inhibit function is not used, pin 3 must be connected to Vi-; otherwise, the output will remain disabled. The inhibit function is useful in applications requiring sequenced start-up, forced shutdown during faults, or power-saving modes.
4. Environmental Adaptability and Reliability Design
4.1 Wide Temperature Operation and Thermal Management
The APF195 operates over a temperature range of -40°C to +85°C without derating. This is the careful thermal design of the IMX 7 series:
High Efficiency: Reduces internal power dissipation, minimizing temperature rise.
No Potting Material: The modules do not use potting material internally, relying on air convection cooling. This avoids stress issues caused by potting material during thermal cycling.
Thermally Symmetric Design: Key heat-generating components are evenly distributed to prevent hot spots.
Case Temperature Monitoring: It is recommended to verify that the case temperature TCTC measured at the specified measuring point does not exceed 95°C (standard version) or 105°C (-8 option) at the maximum ambient temperature. The user must ensure TCTC remains below the specified maximum value under all operating conditions.
4.2 Vibration and Shock Resistance Design
The APF195 has passed rigorous tests such as IEC 60068-2-6 (vibration) and IEC 60068-2-27 (shock), making it suitable for environments subject to mechanical stress. Its mechanical design includes:
Fully Automated Surface Mount: All components are firmly soldered onto a single PCB with no internal wire connections, eliminating the risk of wire breakage due to vibration.
Case Mounting Holes: For extremely high vibration environments, the IMX 7 module itself has case holes for screw mounting, which can further enhance mechanical fixation (though the APF195 mounted on a DIN rail is sufficient for most industrial applications).
4.3 MTBF and Long-Term Reliability
According to MIL-HDBK-217F standards, under Ground Fixed conditions at 40°C, the MTBF for the 40 IMX 7-15-15 is 248,000 hours (approximately 28 years). The MTBF for the 20 IMX 7-24-24-9 used in the APF195 is expected to be at a similar level. This high reliability stems from:
Component Derating: Key components are operated below their rated values, extending lifespan.
Rigorous Factory Testing: Each converter undergoes electrical strength testing, functional testing, and burn-in screening.
ISO 9001 Quality System: Manufacturing complies with ISO 9001 standards.
5. Safety and Installation Requirements
5.1 SELV Output Circuit
Under correct installation conditions and provided the front-end power supply meets isolation requirements, the output circuit of the APF195 can be considered an SELV (Safety Extra-Low Voltage) circuit according to IEC/EN 60950. This means the output voltage is below 60 VDC and has adequate isolation from hazardous voltages, allowing safe operator access.
To achieve SELV output, one of the following conditions must be met during installation:
Option A: The front-end AC-DC power supply provides basic insulation and an output voltage ≤60 V. The output circuit is earthed. The APF195 provides operational insulation. An input fuse and output Zener diodes (already built-in) are required.
Option B: The front-end AC-DC power supply provides double or reinforced insulation and an output voltage ≤60 V. The output circuit is earthed. The APF195 provides operational insulation.
Option C: The front-end power supply output is a TNV-2 circuit (requiring earthing). The APF195 provides supplementary insulation based on its maximum input voltage.
5.2 Input Fuse Requirement
To prevent excessive current flowing through the input supply line in case of a short circuit across the converter input or reverse polarity, an external fast-acting fuse must be installed in the non-earthed input line (typically the positive line). Meggitt recommends:
5.3 Installation Notes
DIN Rail Mounting: Snap the APF195 onto a TH 35 rail, ensuring the latch secures firmly.
Wiring: Connect input and output wires via the PCB pins. It is recommended to use matching terminal blocks for reliable connections.
Electrical Strength Testing: The input/output electrical strength test (1.5 kVDC) was performed at the factory. This test must not be repeated in the field, as it may damage the converter and void the warranty.
Cleaning Agents Protection: The module is not hermetically sealed; prevent cleaning fluids from penetrating the enclosure.
Spacing Requirements: Ensure adequate space around the module for heat dissipation and wiring, and to meet creepage and clearance distances.
V. Application Guide and Selection Recommendations
1. Parallel Application Guidance
When higher current is needed, the two outputs of the APF195 can be paralleled:
Connection Method: Connect Vo1+ to Vo2+, and Vo1- to Vo2-. Connect the load between the paralleled positive and negative terminals.
No Current-Sharing Measures Needed: Internal design ensures automatic current sharing.
Total Output Capability: 0.26 A / 6.2 W.
Note: After paralleling, the total output power must not exceed 6.2 W, and the output voltage remains 24 V.
2. Power Calculation for GSI12x Series Compatibility
| Load Type | Power Consumption per Device | Number of Devices per APF195 | Configuration Method |
| GSI127 | Approx. 3.1 W (estimated) | 1 device | Parallel both outputs to provide 6.2 W total power, meeting inrush demand. |
| GSI124/GSI122 | Approx. 1.5 W (estimated) | 2 devices | Power one device per output; total 6.2 W sufficient. |
| Other 24 V Devices | Depends on consumption | Total consumption ≤ 6.2 W | Distribute load based on specific situation. |
3. Selection Decision Recommendations
3.1 Positioning within the APF Series
The APF195 is the lowest power model in the APF series (6.2 W), designed for powering low-power external devices. The APF series also includes:
APF196: 24 VDC 3 A (72 W), for higher power requirements.
APF197: 24 VDC 5 A (120 W).
APF198: 24 VDC 7.5 A (180 W).
APF200/201/202: Versions with Ex certification.
Users should select the appropriate model based on total load power consumption and whether Ex certification is needed. The APF195 is specifically designed for low-power devices like the GS1xx series galvanic isolation units.
3.2 New Project Selection
For new projects requiring power for 1-2 GSI12x units or other 24 V devices with total consumption ≤6.2 W, and with an input power source of 9.4-36 VDC, the APF195 204-195-000-021 is the ideal choice. Its DIN rail mounting and compact dimensions facilitate integration into control cabinets.
3.3 Legacy System Maintenance
For systems using the earlier APF195 011 version, the 021 version is a direct replacement. Before ordering, confirm compatibility of mounting dimensions and electrical interface (typically they are identical). It is recommended to verify compatibility with Meggitt.
3.4 Ex Compliance Considerations
Although the APF195 itself is not typically used directly in hazardous areas (it is usually installed in a safe area cabinet), it provides power to intrinsically safe equipment located in hazardous areas (e.g., sensors via safety barriers). Therefore, the APF195's own certifications (such as IEC/EN 60950) are necessary for overall system compliance.
3.5 Spare Parts Strategy
For users with multiple VM600 systems, stocking several APF195 units is reasonable, as it is a common external power module that can power various GSI units. The quantity of spares should be determined based on the number and distribution of GSI units in the system.
