Understanding Your Agilent ChemStation 237
Evaluating System Suitability
11
Noise Determination
Noise Calculation by the ASTM Method
Figure 44 Noise Determined by the ASTM Method
ASTM noise determination (ASTM E 685-93) is based on the standard practice
for testing variable-wavelength photometric detectors used in liquid
chromatography, as defined by the American Society for Testing and
Materials. Based on the size of the time range, three different types of noise
can be distinguished. Noise determination is based on peak-to-peak
measurement within defined time ranges.
Cycle Time, t
Long-term noise, the maximum amplitude for all random variations of the
detector signal of frequencies between 6 and 60 cycles per hour. Long-term
noise is determined when the selected time range exceeds one hour. The time
range for each cycle (dt) is set to 10 minutes which will give at least six cycles
within the selected time range.
Short-term noise, the maximum amplitude for all random variations of the
detector signal of a frequency greater than one cycle per minute. Short-term
noise is determined for a selected time range between 10 and 60 minutes. The
time range for each cycle (dt) is set to one minute which will give at least
10 cycles within the selected time range.
Very-short-term noise (not part of ASTM E 685-93), this term is introduced to
describe the maximum amplitude for all random variations of the detector
signal of a frequency greater than one cycle per 0.1 minute.
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