Torque 101 Webinar - How to Choose a Torque Transducer
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Transcript of Torque 101 Webinar - How to Choose a Torque Transducer
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Interface Webinar WednesdayTorque 101with Keith Skidmore
www.interfaceforce.com | 480-948-5555
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Agenda
Definitions What is a Torque
Transducer? Rotary vs. Reaction Shaft vs. Flange Couplings Floating vs. Fixed Bearings
Accuracy & Resolution
Capacity Selection Dual Range RPM Considerations Common Features Torque Applications
Torque 101 | © 2014 Interface, Inc
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Definitions
Torque = Force X Distance
Backlash Couplings
Flexible or Rigid Single or Double Flex
Bearings
Accuracy Resolution Noise Signal to Noise
Ratio RPM
Torque 101 | © 2014 Interface, Inc
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What is a Torque Transducer?
Converts a mechanical input of torque to an electrical output signal – where the signal is directly proportional to the torque input
Consists of a metal spring element, or flexure – like a load cell
Strain gages are bonded to the flexure in a Wheatstone bridge configuration
Torque applied to the sensor causes bending or shear strain in the gaged area, causing the stain gages to change resistance and generating an output voltage signal proportional to torque.
Strain gages go here
Torque 101 | © 2014 Interface, Inc
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Torque Gages
Torque 101 | © 2014 Interface, Inc
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Reaction vs. Rotary
Reaction (static) – measures torque without rotating Normally has a cable attached to it for supplying
excitation voltage to the strain gage bridge and for output of the mV/V signal
Spinning of the sensor is prevented by the attached cable
Rotary (dynamic) – rotates as a part of a system Uses slip rings, rotary transformers, rotating
electronics, rotating digital electronics or radio telemetry to get around the issue of the attached cable
A reaction sensor is at the heart of every rotary sensor
Torque 101 | © 2014 Interface, Inc
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Installations Using Reaction Torque
Torque 101 | © 2014 Interface, Inc
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Installations Using Reaction Torque
Torque 101 | © 2014 Interface, Inc
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Installations Using Rotary Torque
Torque 101 | © 2014 Interface, Inc
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Using Load Cells to Measure Torque
Torque 101 | © 2014 Interface, Inc
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Shaft vs. Flange
Shaft – can either be smooth keyed with keyed shafts coming in either single or double keyed versions. Smooth shaft – more uniform introduction of the
torque into the measuring shaft, ease of assembly and disassembly, zero backlash
Keyed shaft – simpler, cost less, can suffer from wear due to backlash especially in reciprocating applications
Flange – typically shorter than shaft style, have pilots on their flange faces as a centering feature Torque 101 | © 2014 Interface, Inc
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Shaft Style Torque
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Shaft Style Torque
Convenient mounting with standard shaft style coupling
Longer installed length than flange style
Rotating shaft style sensors typically have bearings
Smooth or keyed shafts available
Torque 101 | © 2014 Interface, Inc
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Flange Style Torque
Torque 101 | © 2014 Interface, Inc
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Flange Style Torque
Short install length Better resistance to overhung
moments Can be more convenient to
mount Can be hollow Bearingless rotary torque
sensors tend to be flange style
Torque 101 | © 2014 Interface, Inc
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Specialty Torque
Torque 101 | © 2014 Interface, Inc
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Couplings
Should be used for ALL torque installations
Insure isolation of torque loads
Prevent error and/or damage from extraneous loads
Torque 101 | © 2014 Interface, Inc
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Couplings
Single-flex (half) has a single flex point allows only angular misalignment
Double-flex (full) has two flex points allows both angular and radial misalignment
Torque 101 | © 2014 Interface, Inc
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Couplings
Single-flex Disk coupling
Double-flex Disk coupling
Spiral-cut single flex coupling
Torque 101 | © 2014 Interface, Inc
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Coupling Hub Types
Keyed
Shrink disk for smooth shafts
Clamping for smooth shafts Torque 101 | © 2014 Interface, Inc
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Rope Coupling
Torque 101 | © 2014 Interface, Inc
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Improper Installation
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Too Hot To Handle
Combination of over-rpm use & slipping couplings Torque 101 | © 2014 Interface, Inc
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Floating vs. Fixed
Floating Mount Installations sensor is supported only by the drive and load side
connections (typically single-flex style couplings) a flexible strap keeps the sensor from rotating bearingless sensors are always floating mount
Fixed Mount Installation applies only to sensors with bearings involves attaching the sensor housing to a fixed
support
Torque 101 | © 2014 Interface, Inc
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Floating Mount Installations
Torque 101 | © 2014 Interface, Inc
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Floating Mount Installations
Pros Relatively more misalignment can be tolerated Sensor is protected from radial and thrust load
damage Low cost
Cons Sensor is unsupported during change of test article More unsupported mass Important that the sensor truly floats – should use
spring for anti-rotation
Torque 101 | © 2014 Interface, Inc
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Fixed Mount Installations
Torque 101 | © 2014 Interface, Inc
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Fixed Mount Installations
Pros Sensor supported while connecting & disconnecting
test article Can be better for high speed – shorter rotating
sections
Cons Requires more expensive double-flex couplings Relatively less misalignment capability Sensor can be damaged by unsupported masses,
radial and thrust loads. Bearings or jack-shafts should be used to prevent
this Fixed mount sensor is NOT a bearing block
Torque 101 | © 2014 Interface, Inc
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Other Possible Installations
Torque 101 | © 2014 Interface, Inc
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Bearings
Sensors – Bearings vs. Bearingless Bearing friction Maintain alignment between the rotating
and stationary parts of the sensor Bearingless – always floating mount –
alignment must be maintained Pedestal or Foot Mount sensors MUST
NOT be used as bearing blocks.
Torque 101 | © 2014 Interface, Inc
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Accuracy & Resolution
Usually quoted as a percentage of Capacity A common rating is 0.1% combined error For Example: a 100Nm sensor with
0.1% combined error – will have +/- 0.1Nm error
Other Considerations: Temperature error Noise & resolution Measurement Bandwidth – sample rate
There is ALWAYS a compromise between Accuracy & Resolution and Safety Factor
Torque 101 | © 2014 Interface, Inc
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Accuracy & Resolution
Torque 101 | © 2014 Interface, Inc
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Accuracy & Resolution
Signal types 5V, 10V, Frequency, USB, RS485
Digital vs. Analog Bit resolution Noise
Torque 101 | © 2014 Interface, Inc
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Capacity Selection
Torque sensor capacity MUST accommodate the maximum expected torque for the application
Overload range is reserved for the occasional accident
Calculate average running torque Torque (LB-IN) = [Horsepower] x
[63025]/[RPM]
Apply appropriate Load and Drive service factors
Consider startup and inertia loads Extraneous loading
Torque 101 | © 2014 Interface, Inc
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Capacity Selection
Drive Factors Smooth turbine, DC Motor, 3-phase AC
motor 8-cylinder gas engine, 10-cyclindere
diesel, single-phase AC motor 6-cylinder gas, 8-cylinder diesel, 3-phase
VFD 4-cylinder gas, 6-cylinder diesel, single-
phase VFD <4-cylinder gas, <6-cylinder diesel
Torque 101 | © 2014 Interface, Inc
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Capacity Selection
Load Factors Smooth, constant load devices, fans, centrifugal
blowers Non-reversing, non-constant load or start/stop
devices, extruders, hoists, conveyers, mixers High variable shock or light reversing loads, crushers,
hammer mills, single cylinder reciprocating pumps, vehicle drivelines
Heavy to full torque reversals, undamped torsional vibrations, single and double acting reciprocating compressors
Starting Conditions High inertia load driven by induction motor Soft starts – soft stops
Peak Torque can be 10 or more times the average running torque!!!
Torque 101 | © 2014 Interface, Inc
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Dual Range
Can seem very attractive but are not a “magic bullet”
Excellent choice for certain applications Convenience Less fixture changes More safety factor
Compromise Noise - bandwidth Temperature sensitivity Larger fixtures
Torque 101 | © 2014 Interface, Inc
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RPM Considerations
Observe maximum rpm limit – All sensors have max rating
Balancing – for high speed operation the entire rotating string must be balanced – NOT JUST THE SENSOR
Limit may be bearings, balancing or g-forces on rotating parts
Torque 101 | © 2014 Interface, Inc
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Common Features
Hollow – shaft, electrical or hydraulic pass-through
Scalability Selectable outputs Filter levels – Adjustable vs. Fixed High RPM – Model T25 with special bearing
design
Torque 101 | © 2014 Interface, Inc
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Torque Applications: Reaction – 5412
Brake Test
Torque 101 | © 2014 Interface, Inc
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Torque Applications: Rotary – T5
Fuel Pump Optimization
Torque 101 | © 2014 Interface, Inc
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Torque Applications: Special – T22
Engine Supercharger Power Consumption
Torque 101 | © 2014 Interface, Inc
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Torque Applications: Mini – MRT2
Steering Column Test
Torque 101 | © 2014 Interface, Inc
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Torque Applications: HRDT
SAE Formula Car – Electric Vehicle Characterize electric drive motors
Torque 101 | © 2014 Interface, Inc
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Questions?
www.interfaceforce.com | 480-948-5555
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Thank You!
www.interfaceforce.com | 480-948-5555