Why measure torque?
Kühne Intertech GmbH
Continuous Duty Torque Measurement
During the commissioning, testing and operation of critical turbo-machinery, it is often vital that the precise power
transmitted between drive and driven machinery is known.
This power level can be calculated from various measurements of pressure, temperature and flow using the typical
instrumentation fitted to the machinery train.
The power absorbed by the compressor can be expressed = m Cp ∆T (+ Losses)
(Where ‘m’ is mass flow, ‘Cp’ specific heat and ∆T is temperature rise across the compressor)
However, there are several factors which influence the degree of accuracy to which mechanical power can be derived
by thermodynamic calculation.
Firstly, irrespective of quality of instrument, each sensor system is subject to error and these errors are compounded in
the power calculation. Also the accuracy of this site instrumentation is lower than shop test equipment resulting in
even lower precision.
Secondly, ambient conditions such as temperature and gas composition are not as predicted and this can significantly
affect the validity of the calculation process.
Continuous Duty torque measurement provides a single direct measure of power which is not reliant on other
parameters or affected by variation in site conditions. Accuracy and reliability of power data is therefore substantially
higher than power derived by calculation.
A simple comparison of power measurement methods is shown below;
Comparison of methods Thermodynamic Torque Measurement
# of measurements 10 1
4 – 8 %
Test cost High Low
Benefit of Torque measurement over the complete machine life cycle
o Works string test – base-line performance definition
o Commissioning & Acceptance testing
o Define compressor operating envelope
o Machinery performance monitoring
o Process control
o Condition monitoring strategy
o Re-vamp proving ~ eg re-wheel testing
o Mechanical protection
Kühne Intertech GmbH
Witternstrasse 20, 21107, Hamburg - Germany
Telephone: +49 (0)315001 Fax: +49 (0)40 315060
email: email@example.com - www.kuehne-intertech.de
Typical application examples:
Uncertainties in Mol weight may result in
inaccurate field data.
Precise power data from Torquetronic
defines operating point on power / flow
Accurate operating point applied to
Facilitates optimum operational envelope
below surge condition.
Works site test:
Turbine test; Accurate load measured by torquemeter.
Compressor test; Thermodynamic power measurement data confirmed by
Gas transmission applications typically have low Δt across compressor (eg; 25ºK)
0.1º C temperature measurement error = 80kW power measurement error at
Direct power measurement alleviates problems caused by uncertain gas properties:
Optimised condition and performance monitoring with high accuracy base-line power data:
power value used
as high accuracy
base line data to
Torquemeter power data for performance monitoring system provides base-line value, independent of changes in
ambient conditions, gas composition and time related drift.
Torquetronic Continuous Duty Torquemeter
o Better than 1% accuracy for the life of a machine
o Simple mechanical design
o Unrivalled reliability
o Recognised and accepted by all major end users
o Over 1,000 units installed and operational
o Operates with any brand high performance coupling