News
November 2016 Issue
Zero-point Drift Compensation achieves precise Torque
Measurements for Drive-Train serial component
Application report:
MANNER Sensor Telemetry uses zero-point drift compensation to achieve precise torque
measurements for a drive-train serial component.
Drive-train measurements
When it comes to optimizing the CO2 emissions from vehicles, high-precision measurements of the
frictional losses to the entire drive-train - the so-called powertrain – play a significant role. Friction loss
occurs with all powertrain components: combustion engine, an additional electric motor for hybrid
vehicles, transmission, cardan shafts, differential gear unit and even side shafts.
The total loss of initial energy value drained from petrol or electricity, exceeds often 70% due to the
accumulated loss of these individual powertrain components.
Knowing the loss of each individual component is therefore of utmost importance to achieve overall
optimization. This requires to know simultaneously the dynamic power flow values at the input and
output of each component.
Since the power loss of vehicle's serial components have been significantly optimized in the past, little
potential for optimization remains and the differences between input and output power stay low. In
measurement technology, a 10-fold accuracy for measurements is recommended. Since the differences
have an accuracy around one tenth of a percent, the measuring accuracy of the torque measuring
equipment needs to be very high. In accordance with state-of-the-art technology this can be achieved
today under test bench conditions using high-precision dynamic standard torque measuring technology
in the form of torque flanges.
Due to the complex interactions within the vehicle with different load types, these measurements need to
be carried out in the field (on-road, off-road). Also, the integrated measuring equipment must neither
change the geometry nor the dynamic behaviour of the powertrain as a whole to ensure authentic
measurement results.
This objective can only be achieved by refining the customer serial part directly.
Challenges
Challenges include the sub-optimal material properties of series components in relation to the quality of
the sensor. Despite optimum torque application to serial parts with strain gauges, internal stresses that
are caused by the manufacturing process of the serial part and may result in a zero-point drift, must be
considered. This could completely distort the result, in particular if temperature changes occur during the
measurement. And such changes in temperature are frequently encountered in the field. Under real
environmental conditions and depending on the measurement point, a temperature range of -40°C to
+160°C is required to detect the properties of the vehicle components. Small zero offsets above the
ambient temperature significantly falsify the measured result, making it very hard to implement
meaningful measurements, such as measuring friction over temperature.
The zero-point drift typically is not linear above the ambient temperature. Traditional compensation
methods, e.g. the integration of temperature-dependent resistors with linear characteristics, do not
resolve the problem satisfactorily and are also very expensive in their application.
Solution
MANNER has developed zero-point drift compensation through acquiring zero offsets using
programmable correction curves in the rotating measuring amplifiers (sensor signal amplifiers).
In addition to the established traditional programmability of the measurement range and the zero-point at
23°C it is now possible to remotely configure a corrective zero drift curve for a wide range of ambient
temperatures.
For this purpose, MANNER determines the zero offsets – using the non-compensated sensor part,
multiple ambient temperature points (typically from -50°C to +160°C) and the corresponding deviation for
each temperature point.
These values are then entered into a program for determining the correction parameter. The relevant
correction parameters are downloaded via the telemetry link to the rotating measuring amplifier (sensor
signal amplifier).
The sensor signal amplifier then corrects the zero-point temperature offsets (caused by the change in
ambient temperature) in real-time. The sensor signal amplifier also measures the ambient temperature at
the measuring point.
The result is a measuring point with virtually no zero-point temperature drift (zero drift).
This elevates serial components into highly accurate torque measuring elements which are also suitable
for friction power measurements.
Technical data for the rotating measuring amplifier (sensor signal amplifier):











Measurement channels: Strain gauge and temperature
measurement channels
Measuring range: Remotely adjustable 0.05 mV/V to 12 mV/V
Zero-point: Remotely adjustable: ± 4 mV/V
Measuring signal resolution: 16 bit (digitisation in the rotor)
Sampling rate (max): 6,620 readings/sec
Bandwidth: 1 kHz (2 kHz), -3 dB
Transmission: Inductive (MANNER Sensor Telemetry)
Ambient temperature range: -50°C to +160°C
Precision:
o Zero-point drift (without correction): 0.003%/°C
o Zero-point drift (with correction): 0.001%/°C
Non-linear drift correction
Gain drift: 0.003%/°C