How is the accuracy specification of a Gantner Instruments measurement module determined, and what factors does it include?
Introduction
Measurement accuracy refers to the degree of closeness between a measured value and the true value of the quantity being measured. In other words, it is a measure of how well a measurement reflects the actual or real value of the quantity. High measurement accuracy indicates that the measured values are very close to the true values, while low accuracy implies a greater divergence between the measured and true values.
Accuracy is a critical aspect in various fields such as science, engineering, manufacturing, and research, where precise and reliable measurements are essential. It is often expressed as a percentage or in terms of a specific unit of measurement. Calibration, regular maintenance, and adherence to standardized measurement procedures are important for ensuring and improving measurement accuracy.
How is the measurement accuracy of a module specified?
The accuracy specification on the datasheet for Q.series measurement modules is determined based on the % full scale (%FS) of the module channel's measurement range. Furthermore, the accuracy is influenced by the environmental conditions where the data acquisition hardware is situated. In a typical environment, the accuracy is 0.01%; in a controlled environment, it is 0.025%; and in an industrial area, it is 0.05%.
Example:
The measurement accuracy for a ±2 mV/V load cell with a ±50'000 N range, 10 V excitation, and ±2.5 mV/V input range is calculated as follows:- Error in mV/V = ±2.5 mV/V * 0.05% (for an industrial environment) = ±0.00125 mV/V
- Since 2 mV/V corresponds to ±50'000 kN, 1 mV/V is equivalent to ±25'000 kN
- Error in engineering units = ±0.00125 mV/V * ±25'000 N = ±31.25 N
What errors are included in the accuracy specification?
The zero offset and gain offset are integral components of our calibration standards when determining accuracy specifications. For analog input modules, these specifications account for the temperature effects of both zero offset and gain drift, with units expressed per 10 degrees Kelvin, presented as separate line items.
Datasheet example:
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When addressing input noise errors, we incorporate them into the specifications using a standard confidence factor following the Guide to the Expression of Uncertainty in Measurement (GUM). GUM is a widely recognized and internationally accepted document published by the Joint Committee for Guides in Metrology (JCGM). These errors are determined according to EN 61326-1:2006, considering the noise suppression electronics.
The calculations cover channel-to-channel, channel-to-ground, and channel-to-bus voltage isolations, set at 500 VDC for standard Q.series and Q.series X modules, and 1200 or 1500 VDC for the higher isolation A12x modules. Testing and specifications involve noise pulses up to 1000 VDC, with continuous testing up to 250 VDC. Any noise error exceeding these levels is not included in the accuracy specifications due to challenges in determination.
Datasheet example:
