calibration
Usage
>> calibration <channel_label> [ equation | datetime | offset | slope | c0 ... cN | x0 ... xN | n0 ... nN ]
Security
Unsafe.
Description
Reports or sets information regarding the most recent calibration for the channel specified by <channel_label>, which is a required parameter in all cases (see channel). Calibrations cannot be created or deleted. They are tightly coupled to the channels for which they apply and as such the associated <channel_label> must be specified to access them. The number and types of coefficients reported, or required when setting, will vary depending on the channel type (see channel).
Some sensor types have complicated equations with many coefficients, and the equation may also use the output of one or more of the other channels in the logger for correction or compensation purposes. This is a powerful facility, but requires a lot of information; the calibration command helps to manage that information.
Coefficients are arranged in three groups, c0…, x0…, and there is a further group n0… of cross-channel reference labels. The purpose and function of each group will be described below. The groups may also be referred to by name; c, x, or n.
All parameters might be obtained by issuing the command without providing any specific parameter names. Parameters may also be requested individually, or in any combination, by name. Coefficients in each group may be requested all together by using one of the group names, c, x or n. Requesting an item which does not exist (eg. c3 for a linear sensor) may result in either an error message, or a response such as c3=na.
When setting parameters, there are further restrictions which must be followed:
The equation and n… coefficients are read only.
datetime=<YYYYMMDDhhmmss> may accompany any changes to coefficient values, so that the reported date and time reflects the most recent change. If it is not provided when modifying coefficients, the parameter is updated with the current date and time (see the clock command).
Descriptions of the individual parameters are given below.
equation is the type of formula used to convert raw data readings to physical measurement units. The values for the core equations are shown below as examples; see the section Calibration Equations and Cross-channel Dependencies for details of all supported equations.
tmp temperature
lin linear
qad quadratic polynomial
cub cubic polynomial
datetime is reported and set using a <YYYYMMDDhhmmss> format. It is the date and time of the most recent calibration change for the channel.
c0, c1… are the primary coefficient values, reported as floating point numbers using a format with a mantissa and exponent; for example 3.3910000e+003. When setting coefficients, any simple format compatible with floating point representation may be used; for example 11, 11.000 or 1.10e+1 would all be accepted.
These coefficients apply to a "core" equation which yields a basic value for the parameter. In many cases this is all that is needed, and the x and n groups are not required. The exact function of each coefficient depends on the equation used.x0, x1… are required and reported for only some equation types, namely those which employ cross-channel compensation or correction of the primary value using one or more inputs from other channels in the logger. x0, x1… are also coefficient values which follow the same rules as the c group. The exact function of each coefficient depends on the equation used.
n0, n1… apply only to some equation types, those using cross-channel compensation or correction. They are only ever reported; they are set at the factory and can not be changed. They are not coefficients, but (in general) the labels of other logger channels whose data are also inputs to the equation for channel <channel_label>. This permits output data to depend on more than one channel; for example, to be corrected for temperature dependencies.
Most equations which use the x0, x1… coefficients will require at least one "n" entry. The logger may also have 'derived parameter' channels, which have no measurement channel of their own, but an output value which is computed from other measured channels: a good example would be salinity, which is a function of conductivity, temperature and pressure. In such cases n0, n1, n2 are required to tell the logger which input channels to use.
There is one special case when the value of an "n" label may be the text field "value". This can be set only at the factory, and applies when an equation requires a correction term using a parameter which the logger does not measure. In this case the default parameter set by the command parameters will be used.
offset, slope are provided to permit users to apply a simple linear adjustment to the final value. They are not part of the instrument's official calibration, and RBR Ltd. keeps no record of their values. They can be used, for example, to give a rough correction in the field when a proper re-calibration is not possible. Using these parameters as a permanent calibration correction is not recommended; many sensors have a non-linear response, or depend also on values from other channels. If a sensor requires recalibration, it should be returned to RBR Ltd for proper handling.
Please refer to the section Calibration Equations and Cross-channel Dependencies for a complete list of the equations which the logger uses, and for further discussion of cross channel dependencies.
Examples
>> calibration voltage_01
<< calibration voltage_01 equation=lin datetime=20171218175005 offset=0.0000000e+000 slope=1.0000000e+000 c0=9.9876543e+000 c1=7.5642301e+000Queries the calibration for a single channel with the label voltage_01.
>> calibration voltage_01 c0
<< calibration voltage_02 c0=9.9873456e+000Queries a single parameter for the calibration of a single channel.
>> calibration voltage_00 datetime=20171203134201 c0=9.9873456 c1=7.564
<< calibration voltage_00 datetime=20171203134201 c0=9.9873456e+000 c1=7.5640000e+000Setting the calibration for a channel.