Tag: motorized test stand

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.

Conclusion:

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.

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.

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.

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, 0.02, 0.03…50.00.

Why is accuracy better when the sensor is calibrated on the test frame rather than independently?

When the sensor is mounted to the test frame, it is considered an integrated, single measuring instrument. By contrast, when the sensor and test frame’s electronics are calibrated independently against master calibration equipment, tolerances accumulate, reducing overall accuracy.

±0.2% FS accuracy is well within the requirements for virtually any test standard. If higher accuracy is desired, integrated calibration is suggested. This service is not offered by Mark-10, however, field calibration instructions are provided in the user’s guide.