SParams#
- class mqr.spc.SParams(centre: float, nsigma: int = 3, name: str = 'S')#
S (sample standard deviation) control parameters.
Use this class to construct traditional S charts. In addition to construction using class attributes, SParams can be constructed from historical data.
- Attributes:
- centrefloat
Expected value of the process stddev.
- nsigmafloat, optional
Distance in standard errors (of the stddev) of the upper and lower control limits from the centreline.
- namestr, optional
Name of the control method.
Methods
asdict()Returns a dict representation of this class.
from_data(samples[, nsigma])Constructs SParams from reference samples.
lcl(nobs)Calculates the lower control limits for samples with sizes in nobs.
se(nobs)Standard error of the standard deviation
statistic(samples)S statistic; the sample standard deviation.
target()Expected value of the standard deviation.
ucl(nobs)Calculates the upper control limits for samples with sizes in nobs.