3500/50 - Tachometer Module

3500/50 - Tachometer Module 3500/50 - Tachometer Module

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Part Number: 3500/50
Manufacturer: Bently Nevada
Series: 3500
Product type: Tachometer Module
Operating Temperature: -30°C to +65°C
Storage Temperature: -40°C to +85°C
Humidity: 95%, non-condensing
Availability: In Stock
Country of Manufacture: United States (USA)

Functional Description

3500/50 is a Tachometer Module designed and developed by Bently Nevada. The Module represents a sophisticated advancement in monitoring technology, designed to provide accurate and reliable measurements of shaft rotative speed, rotor acceleration, and rotor direction within various industrial applications. This module, boasting two channels, showcases its adaptability by accepting inputs from a variety of sources such as proximity probes or magnetic pickups, with the exception of certain cases as indicated. At its core, the primary purpose of the Tachometer Module is to ascertain critical parameters of rotational machinery. By analyzing the input signals derived from proximity probes or magnetic pickups, the module accurately determines the rotational speed of a shaft or rotor. This measurement holds immense importance in assessing the operational state of the machinery, as it directly reflects the speed at which key components are functioning.


  • It is also equipped to evaluate rotor acceleration. Rotor acceleration data is invaluable for assessing the behavior of machinery during startup, shutdown, or transient operational phases. This insight aids in understanding how quickly a rotor accelerates or decelerates, thereby helping to identify irregular patterns that might indicate mechanical imbalances or anomalies.
  • The module's proficiency extends further by enabling the determination of rotor direction. This feature is particularly beneficial when analyzing machinery that can operate in both forward and reverse directions. By identifying the direction of rotation, operators and maintenance personnel can better comprehend the operational state and anticipate potential issues associated with reversing machinery.
  • One of the most impressive aspects of the Module is its capacity to not only gather data but also to process it intelligently. User-programmable alarm setpoints allow for customization and adaptation to specific operational requirements. By configuring these alarm setpoints, operators can define threshold values that trigger alarms when breached. These alarms serve as early indicators of potential problems, enabling proactive intervention to prevent catastrophic failures and unplanned downtime.
  • Crucially, the programming of the Tachometer Module is streamlined through the use of the 3500 Rack Configuration Software. This software empowers users to configure, calibrate, and fine-tune the module's settings with ease. The intuitive interface of the software simplifies the process of programming the module according to the unique needs of the machinery being monitored.
  • The module offers a versatile configuration that enhances its functionality within the rack system. One noteworthy feature is its ability to provide conditioned Keyphasor signals directly to the backplane of the rack. This innovation eliminates the requirement for an independent Keyphasor module within the rack setup, streamlining the configuration and making the monitoring process more efficient. Incorporating a Keyphasor module in the rack demanded additional resources and space.
  • However, with the capability to supply conditioned Keyphasor signals, this demand is mitigated, allowing for a more compact and organized setup. This streamlining not only optimizes the use of the rack's available slots but also simplifies the wiring and interconnection intricacies that would otherwise be associated with a separate Keyphasor module.
  • The module isn't solely limited to the elimination of redundant modules. It is equipped with a peak hold feature that adds another layer of functionality to the monitoring process. This peak hold feature serves to capture and retain critical operational data. Specifically, it records and stores key metrics such as the highest operational speed, highest reverse speed, or the count of reverse rotations, contingent on the channel type that the user selects.
  • The significance of this peak hold functionality cannot be understated. By retaining peak values, the 3500/50 empowers operators and maintenance personnel with valuable insights into the machine's performance history. This historical data aids in identifying patterns, irregularities, and potential issues that might otherwise go unnoticed. Such information contributes to predictive maintenance strategies and proactive decision-making, ultimately enhancing the reliability and longevity of the machinery being monitored.
  • A noteworthy aspect of the peak hold feature is its user-friendly design. The ability to reset the recorded peak values provides flexibility and adaptability. Operators can reset the stored values as needed, allowing for seamless tracking of peak performance across different operational phases or maintenance cycles.

Signal Conditioning

  • The Speed Input feature of the 3500 Tachometer Module offers a comprehensive range of capabilities tailored to accurately measure rotational speeds of machinery. This module's versatility and precision make it a cornerstone in industrial monitoring systems, providing engineers and operators with the crucial insights needed to maintain machinery reliability and optimize performance.
  • The Speed Input function of the 3500 Tachometer Module showcases an impressive range, accommodating a broad spectrum of rotational events per revolution. It is capable of processing input frequencies from as low as 0.0039 events per revolution to a high of 255 events per revolution. This adaptability caters to diverse applications and allows the module to be utilized across various industries and machinery types.
  • A pivotal aspect of the Speed Input is its capacity to handle a maximum full scale range of 99,999 revolutions per minute (rpm), illustrating its suitability for high-speed applications. The module's upper limit of 20 kHz for maximum input frequency showcases its capability to swiftly process incoming data, even in dynamic operational scenarios.
  • For proximity transducers, the Speed Input demonstrates its precision by accommodating a minimum input frequency of 0.0167 Hz, equivalent to 1 revolution per minute for a configuration involving 1 event per revolution. Passive magnetic pickups, on the other hand, are supported with a minimum input frequency of 3.3 Hz, demonstrating the module's compatibility with different types of sensors commonly used in industrial environments.
  • The RPM accuracy specifications for the 3500 Tachometer Module provide a clear picture of its reliability in delivering precise data. When dealing with speeds below 100 rpm, the module boasts an impressive accuracy of ± 0.1 rpm, ensuring even the minutest variations are accurately captured. For speeds ranging from 100 to 10,000 rpm, the accuracy remains exceptional at ±1 rpm, maintaining reliability across a broad operational range. As the speed climbs further to the range of 10,000 to 99,999 rpm, the accuracy is maintained at ± 0.01% of the true shaft speed, underscoring the module's ability to handle high-speed applications with impeccable precision.
  • The RPM/Min Accuracy specification of ± 20 rpm/min highlights the module's ability to capture changes in rotational speed over time. This feature is particularly valuable for assessing acceleration or deceleration patterns during start-up, shut-down, or transient phases of machinery operation.
  • In conclusion, the Speed Input feature of the 3500 Tachometer Module showcases a remarkable fusion of adaptability and accuracy. Its ability to accommodate a wide range of input frequencies, coupled with its precision across various rpm ranges, positions it as a cornerstone in machinery monitoring. By providing dependable and precise data, the module empowers operators and maintenance personnel to make informed decisions, enabling predictive maintenance strategies that enhance machinery reliability and operational efficiency.


  • OK LED: Indicates when the Module is operating properly.
  • TX/RX LED: Indicates when the Module is communicating with other modules in the 3500 rack.
  • Bypass LED: Indicates when the Module is in Bypass Mode.


  • 2-Channel Module
  • Accepts Input from Proximity Probes or Magnetic Pickups
  • Peak Hold Stores Highest Speed, Highest Reverse Speed, Number of Reverse Rotations
  • Able to Reset the Peak Values
  • Supplies Conditioned Keyphasor Signals to the Backplane of the 3500 Rack

WOC is happy to assist you with any of your Bently Nevada requirements. Please contact us by phone or email for pricing and availability on any parts and repairs.


What is 3500/50?
It is a Tachometer Module designed and developed by Bently Nevada.

Are Tachometer Modules suitable for overspeed protection systems?
No, It is not intended to be used as components of overspeed protection systems. They lack the necessary protective redundancy and response speed required for reliable and safe operation in overspeed protection applications.

Can I rely on Modules as the sole speed control mechanism?
No, the Modules do not possess the capabilities for serving as a primary speed control system. Their design focuses on measuring speed-related parameters and generating alarms based on user-set thresholds, rather than actively regulating machinery speeds.

What is the purpose of the analog proportional output in Modules?
The analog proportional output in these modules is designed for supplementary functions such as data logging, chart recording, or display purposes. It's not intended for direct control of machinery speed or any critical control applications.

Can I rely on Bently Nevada Tachometer Modules for protective redundancy?
No, these modules are not engineered to provide protective redundancy. They are not equipped with the necessary design features and characteristics to fulfill the requirements of redundancy, which is crucial in critical safety applications.

Can the Tachometer Modules serve as a primary overspeed alarm system?
While Tachometer Modules offer speed alert setpoints, they are only suitable for annunciation purposes. They can notify operators of potential speed deviations, but they should not be solely relied upon as a primary overspeed protection system.