Mark-10 defines accuracy as a percentage of full scale of the
instrument. To determine the measurement error as an actual
load value, multiply the accuracy percentage by the instrument’s capacity.
Example 1 – M5-50 force gauge:
The accuracy is ±0.1% of full scale (FS). Multiply ±0.1% by 50 lbF,
which equals ±0.05 lbF. This means that any displayed reading may be
higher or lower by up to 0.05 lbF. For example, if the displayed
value is 30.00 lbF, the true reading will be ≥29.95 lbF and ≤30.05 lbF.
Example 2 – Plug & Test® indicators and sensors:
The accuracies of the sensor and the indicator must be added together.
Models 7i and 5i indicators have accuracy values of ±0.1% FS,
while the Model 3i is rated at ±0.2% FS. Using the example of a
Series R50 torque sensor with Model 3i indicator, add ±0.35% to ±0.2%,
which equals ±0.55%. In a specific example for the Model MR50-12,
the accuracy becomes ±0.55% x 135 Ncm = ±0.7425 Ncm.
Percentage of Reading:
Because of these fixed errors, lower measured values will be more
inaccurate as a percentage of reading.
Further using the example of an M5-50 force gauge, a fixed error of
±0.05 lbF represents a higher error as a percentage of reading for
a load of 1.00 lbF than 30.00 lbF.
To calculate the error as a percentage of reading, divide the fixed
error by the measured value. For a 1.00 lbF load, the fixed error
equals ±0.05 ÷ 1.00 lbF = ±5% of reading. For a 30.00 lbF load,
the fixed error equals ±0.05 ÷ 30.00 lbF = ±0.17% of reading.
Because of the relationship between load and accuracy, we recommend
selecting an instrument capacity as close as possible to the
maximum measured load.
Sampling rate is defined as the rate at which the instrument’s
electronics communicate with its load sensor. A faster sampling
rate more accurately captures the peak load which occurred during
the test. This is especially apparent in applications where the
load builds up and falls very quickly – such as the break testing
of glass or ceramics. The graphs below illustrate the advantage
of a fast sampling rate:
The graph at left shows that an instrument with slower sampling
rate may not accurately detect the true peak. In the graph at
right, the faster rate accurately captures the true peak.
Sampling Rate vs. Output Rate
While Mark-10 instruments internally sample at up to 14,000 Hz,
a typical streaming output rate to MESURgauge software is
approximately 25 - 50 Hz. If a faster data collection rate is
required, our Series 7 force gauges and indicators can collect
data at up to 14,000 Hz, store the data internally, and
bulk-download the data to a PC when the test is complete.
Capacity x Resolution
This value represents the maximum measurable load. All available
capacities are listed for each available unit of measurement.
All instruments measure from 0 to the indicated capacity.
This value represents the smallest measurable increment.
For Plug & Test® sensors, the resolution depends
on which indicator is used. Refer to the Capacity x Resolution
tables on the particular sensor’s webpage or data sheet.
Example - M5-50 Force Gauge:
Pound-force Capacity x Resolution for the M5-50 force gauge
is 50 x 0.01 lbF. This means that the gauge measures from
0 to 50 lbF, with increment size of 0.01 lbF, i.e., 0, 0.01,
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Hard vs. Soft Joints
Rundown fixtures contain an internal spring which dampens
the rate of increase in torque when a power tool is used,
thereby contributing to a more accurate torque measurement.
Two fixtures are offered, with different internal spring rates,
to address a wide range of applications. Select the AC1066-1
to simulate a soft joint with gradual torque buildup, or AC1066-2
to simulate a hard joint with faster torque buildup.
Either fixture is suitable for the full range of torque up to
100 lbFin (11.5 Nm).
Examples of hard and soft joints are provided below: