The TVS™ and TVS+™ systems are optical, non-contact sensors for torque measurement of rotating shafts without strain gauges, telemetry, or in-line torque cell. The same instrument will work for shafts of any size, making it a very versatile and portable tool.
The TVS™ family of instruments is well adapted to both permanent monitoring and temporary measurements of power and torque in rotating machinery. TVS™ and TVS+™ accurately measure speed and torque, allowing full power measurement. As an added bonus, the TVS™ family of sensors also measures torsional vibration and the TVS+™ sensor measures axial displacement of the coupling.
Torque Measurement of Rotary Shafts
Torque measurement helps you plan your machine preventive maintenance intelligently. Accurate torque measurement is critical to understanding the health of the rotating system. Torque monitoring over time can alert the user to system degradation. For example, wear in pump seals decrease the pump efficiency over time; these show as a variation in torque over time. Monitoring changes in torque through continuous measurement of shaft twist is a reliable way to alert an operator to the need of preventive or corrective maintenance.
Continuous torque monitoring is also a reliable way to detect system aberrations or over-torque conditions that are leading indicators of system failure. Setting alarms based on detection of these anomalous torque events allows operators to perform inspection of the machinery, avoiding further degradation of the equipment.
Sensors for Rotary Torque Measurements
There are three main methods of torque measurement: in-line systems (torque cells, torque meters, dynamometers), sensors attached to the surface of the shaft (typically strain gauge-based systems), and optical systems.
In-line systems offer good accuracy and can be calibrated before mounting onto the drivetrain. But they also present several disadvantages. First, they are part of the drivetrain and are often considered a weak link, either from a strength or deflection perspective. Second, they must be precisely aligned like the rest of the drivetrain, which increases the total complexity of the system. Third, they cannot be easily retrofitted on an existing installation and need to be carefully planned for.
Strain gauges require complex installation. They must be mounted by professionals and positioned in the correct orientation. They also need a method to pass the signal from the rotary shaft to a static base, either through telemetry or slip rings.
Optical systems in comparison are very easy to install on any new or existing shaft. The TVS+™ system only requires attachment of two self-adhesive labels to the shaft. The labels and adhesive have been carefully selected for their ruggedness and resist both high rotation speeds and high temperature. Once the two labels are attached, point the optical probes at the labels and the system is ready to acquire data. Optical systems require no complex installation, no careful alignment of the drivetrain, no telemetry, no slip rings.
Non-Contact Torque Measurement of a Rotating Coupling or Shaft
The TVS+™ system measures torque and speed of rotary shafts. It takes less than an hour of downtime to instrument the turbomachinery, typically the coupling, with the self adhesive labels that enable torque measurement. This makes the TVS+™ system an ideal tool for troubleshooting and diagnostics.
Additionally, combining the torque and speed measurement from TVS™ or TVS+™ results in a high accuracy measurement of shaft power and enables precise calculation of system efficiency.
Absolute vs. Relative Torque Measurement
Do you need to monitor absolute torque or relative torque? The TVS+™ system measures absolute twist, which can be used to measure absolute or relative torque. However, users must understand that high precision measurement of absolute torque places a premium on accurate calibration.
For many users, the critical parameter is the change of torque over time. A decrease in torque is an indicator of system degradation. This can be due to leaks, wear in seals or bearings, misalignment, and many other factors. Conversely, users can track improvements they make to rotating machinery by tracking the resulting increase in torque.
The TVS+™ system tracks absolute twist. The measurement of the twist angle between the two probes does not require any calibration. For users who are only concerned about changes in torque, the goal is to measure torque differences from a baseline condition. In that case, the measurement of twist – or change in twist over time – is sufficient, and there is no need to perform any calibration.
Absolute torque can be calculated based on the geometry and material properties of the shaft. A twist-to-torque conversion factor can be entered in the TVS+™ system to read absolute torque directly. If high precision measurement of absolute torque is required (beyond the uncertainties of a calculated twist-to-torque conversion factor), a physical calibration is required. This is done by applying a known torque across the coupling and measuring its angular deflection. Note that in-line torque cells or strain gauge systems also require similar calibration for accurate readings. One advantage of the optical system is that readings do not drift over time as the twist readings are permanently calibrated.
Accurate shaft speed measurement
Hold your system accountable to the speed limits. Speed measurement helps you ensure that your system is operating as intended. Speed is critical in a variety of applications across industries.
- In power generation speed changes can lead to fluctuations in frequency of the AC power produced.
- In films and paper manufacturing variations in roller speed can lead to inconsistent product dimensions and scrap.
- In automotive and industrial environments variation in speed can be an identifier of unbalance in the system.
Taking accurate real time speed measurements can allow you to automate system shut down before failure, identify out of tolerance product, and account for variation in your manufacturing system. Our TVS™ system accurately measures speed and speed variation of your rotating assembly.
Using TVS™ to Measure Speed, Torque, and Power
Measurements of speed, torque and power can be achieved in several ways, but the greatest advantages of our optical system approach are that:
- Optical systems are intrinsically safe and immune to electromagnetic interference. The optical probes can be located in any ATEX zone. Long optical leads allow the instrumentation to be located remotely, away from the hazardous area. Instrumentation can also be enclosed in an ATEX rated enclosure.
- The sensor does not need to make contact with the shaft in order to give high accuracy measurement. Rotating systems are sensitive to balance and loading conditions, by opting for a non-contact sensor you avoid these potential risks.
- Optical sensors are easy to install, with very little to no modification to the shaft. One version of our product, simply called TVS™, does not require any marking or change to the shaft. Another version called TVS+™ only requires a rugged label to be affixed in two places on the shaft.
- Installation of the system can be done both retroactively on existing systems or designed into the system upon conception.
The ease of installation combined with the minimally invasive aspect of the sensor system makes it an ideal measurement tool for a variety of applications and environments. Its portability also makes it ideal for temporary installation such as startup and commissioning of new couplings, compressors or motors; or troubleshooting existing installations.
The TVS™ sensors can also be integrated with a coupling for permanent monitoring of torque and power.