Pepperl+Fuchs KFU8-UFT-EX2.D Retrofit-Compatible Frequency Converter

Pepperl+Fuchs KFU8-UFT-EX2.D Retrofit-Compatible Frequency Converter for Legacy Systems

The Pepperl+Fuchs KFU8-UFT-EX2.D is a DIN rail-mounted, intrinsically safe frequency converter designed for NAMUR-compatible sensor interfaces in hazardous area applications. As legacy automation systems age and original spare parts become increasingly difficult to source, the KFU8-UFT-EX2.D has become a critical retrofit component for engineers tasked with modernizing older control architectures without full system replacement. Whether you are managing a brownfield upgrade, extending the service life of an existing control cabinet, or replacing a discontinued module in a live production line, this unit delivers the signal conditioning performance and installation compatibility required for a smooth transition.

Designed for Zone 1 and Zone 2 hazardous environments, the KFU8-UFT-EX2.D accepts NAMUR-standard frequency signals from proximity switches and flow sensors installed in Ex zones, converting them to standard output signals suitable for modern PLC input modules. Its compact 20 mm housing fits standard K-System backplane carriers such as the KFD2-GUT-Ex1.D and KFD2-SOT2-Ex2 series, making it directly interchangeable in existing rack configurations without requiring panel rework or additional mounting hardware.

Upgrade Compatibility Table

Retrofit Planning for Existing Automation Systems

Successful integration of the KFU8-UFT-EX2.D into a legacy control system requires a structured pre-installation review. Engineers should begin by auditing the existing K-System carrier rail to confirm available slot positions and backplane power budget. In many older installations, the power supply module — often a KFD2-EB2 or equivalent segment power conditioner — may be operating near its rated output current. Adding or replacing modules without verifying the power margin can cause intermittent faults or nuisance trips on adjacent channels.

Terminal wiring is the next critical checkpoint. The KFU8-UFT-EX2.D uses a standard K-System field-side terminal layout, but older installations may have used custom cable labeling or non-standard color coding. Before disconnecting any wiring, photograph the existing terminal block and cross-reference against the original loop drawing. Pay particular attention to the NAMUR sensor loop polarity — reversing the field wiring will prevent the module from detecting the sensor’s switching state correctly.

For systems that also include KFD2-SR2-Ex2.W relay modules or KFD2-CD-Ex1.32 solenoid drivers in the same cabinet, confirm that the backplane segment boundaries are correctly defined. K-System carriers segment power independently, and a module installed in the wrong segment may receive incorrect supply voltage or share a common ground with incompatible module types.

Where the existing PLC is an older Siemens S5 or early S7-300 platform, the digital input card connected to the KFU8-UFT-EX2.D output may require a pull-up resistor or input filter time adjustment to correctly read the transistor output signal. Modern S7-1500 or Allen-Bradley ControlLogix I/O modules are generally more tolerant of signal edge timing, but the PLC program scaling for frequency-to-engineering-unit conversion must still be validated after module replacement. If the original program used a fixed pulse count per unit of flow or speed, verify that the new module’s output pulse characteristics match the legacy unit’s specifications.

In control cabinets where space is constrained, the 20 mm width of the KFU8-UFT-EX2.D is a significant advantage. Unlike some third-party alternatives that require 22.5 mm or 45 mm slots, this module maintains the original footprint, preserving cable routing and avoiding the need to relocate adjacent modules such as KFD2-UT2-Ex2 temperature converters or KFD2-VR-Ex1.26.160 valve remote indicators. This is particularly important in offshore or petrochemical installations where panel modification requires additional hazardous area certification review.

For sites migrating from older Pepperl+Fuchs KFU8 or KFA6 series modules to the current KFD2 platform, the KFU8-UFT-EX2.D serves as a transitional component that maintains backward compatibility with existing NAMUR sensor wiring while delivering improved diagnostic transparency. When combined with a KFD2-GUT-Ex1.D gateway or a segment coupler for PROFIBUS PA or FOUNDATION Fieldbus migration projects, the module can be retained in the hardwired I/O layer while higher-level communication infrastructure is upgraded independently — reducing the scope and risk of each individual migration phase.

Downtime Control During System Migration

Minimizing production downtime during a module replacement or system upgrade is the primary concern for most maintenance teams. For the KFU8-UFT-EX2.D, the replacement procedure can typically be completed within a single planned maintenance window if the preparation work is done in advance. The key steps are: obtain and verify the replacement unit against the original module’s label and order code before the maintenance window begins; prepare a pre-tested spare with a functional test report confirming output signal behavior at the rated frequency range; and ensure the PLC is placed in a safe operating mode — either manual control or a defined fallback state — before the field loop is de-energized.

Because the KFU8-UFT-EX2.D is a plug-in K-System module, physical replacement does not require rewiring the field cable. The field-side terminal block remains in place; only the module body is removed and replaced. This significantly reduces the risk of wiring errors during the swap and allows the field loop to be re-energized and verified within minutes of module insertion. After re-energization, confirm the NAMUR sensor loop current is within the normal operating range (typically 1–2 mA for a de-energized NAMUR sensor and 6–8 mA for an energized sensor) before releasing the PLC input to automatic control.

For sites where the KFU8-UFT-EX2.D feeds a critical flow measurement or speed monitoring loop, consider implementing a temporary bypass using a portable signal simulator connected to the PLC input during the swap interval. This allows the control system to maintain a known-good signal state while the field loop is open, preventing spurious alarms or automatic shutdowns triggered by a loss-of-signal condition. Once the replacement module is confirmed operational, the bypass is removed and the live sensor signal is restored to the PLC.

Where multiple modules are being replaced in a single campaign — for example, during a scheduled turnaround or annual shutdown — batch the replacements by backplane segment to minimize the number of times the segment power must be cycled. Each power cycle introduces a brief initialization period during which all modules in the segment perform self-diagnostics. Grouping replacements by segment reduces total initialization time and allows the maintenance team to verify each segment’s output status before moving to the next.

Retrofit Support FAQ

Q1: Is the KFU8-UFT-EX2.D a direct replacement for older KFU8 series frequency converters?
Yes. The KFU8-UFT-EX2.D is designed as a drop-in replacement for earlier KFU8 series frequency converter modules within the K-System platform. The backplane connector, housing width, and field terminal layout are compatible with existing K-System carriers. However, always cross-reference the original module’s order code and wiring diagram to confirm input/output configuration before installation, as some early KFU8 variants had application-specific output configurations.

Q2: What commissioning checks are required after installation?
After physical installation, verify the NAMUR sensor loop current at the field terminals, confirm the PLC input is receiving the correct signal state (energized/de-energized), and validate the frequency-to-engineering-unit scaling in the PLC program. If the system uses an HMI, check that the process variable display reflects the correct value at both zero-flow and full-scale conditions. Document the as-found and as-left readings for the maintenance record.

Q3: Does the unit ship with a functional test report, and what does the 12-month warranty cover?
Yes. Each KFU8-UFT-EX2.D supplied by NINERMAS is functionally tested prior to shipment and ships with a test report confirming output signal performance. The 12-month warranty covers manufacturing defects and functional failures under normal operating conditions from the date of shipment. It does not cover damage resulting from incorrect installation, overvoltage, or operation outside the rated environmental conditions.

Q4: Is stock available for immediate shipment, and can you support multiple-unit orders for a plant-wide retrofit campaign?
NINERMAS maintains inventory of the KFU8-UFT-EX2.D to support both single-unit emergency replacements and multi-unit retrofit campaigns. Lead times and available quantities can be confirmed by contacting our sales team directly. For large-volume orders, we recommend submitting a bill of materials for the full retrofit scope so we can confirm availability across all required part numbers simultaneously.