RParams#
- class mqr.spc.RParams(centre: float, sigma: float, nsigma: float = 3, name: str = 'R')#
R (sample range) control parameters.
Use this class to construct traditional R charts. In addition to construction using class attributes, RParams can be constructed from sample range or historical data.
Note
Using sample range to estimate process standard deviation can be inefficient. See Efficieny of estimates of process standard deviation.
- Attributes:
- centrefloat
Expected value of the process range.
- sigmafloat
Standard deviation of the process.
- nsigmafloat, optional
Distance in standard errors (of the range) 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 RParams from reference samples.
from_range(r_bar, nobs[, nsigma])Constructs RParams from process range.
lcl(nobs)Calculates the lower control limits for samples with sizes in nobs.
se(nobs)Standard error of the range.
statistic(samples)R statistic; the sample range.
target()Expected value of the sample range.
ucl(nobs)Calculates the upper control limits for samples with sizes in nobs.