iso_convert_signals: Convert signal units in continuous flow and dual inlet files
In KopfLab/isoprocessorCUB: IRMS data processor

This function can be used to convert the intensity units of a collection of iso_files to a scaled unit (e.g. from mV to V, or nA to mA) or different unit (e.g. from mV to nA or vice-versa). The original signal intensity units are inferred from the naming of the intensity columns. The new units must be a voltage (V) or current (A) but can have any valid SI prefix. Conversion from voltage to current and vice versa requires information about the resistors used in the op amp. This information is automatically retrieved during file read for file formats that contain resistors values (e.g. dxf and did) and are read with the read_method_info=TRUE parameter (see iso_get_resistors_info for details on how to access resistor values in read files). If resistor values are not set in a file, it will not allow automatic conversion between voltage and current. Instead, the R and R_units parameters can be used to provide specific resistor values. However, if R is set, these values will be used for all passed in iso_files.

1	iso_convert_signals(iso_files, to, R, R_units = NA, quiet = default(quiet))

`iso_files`	collection of iso_file objects
`to`	what signal unit to convert to
`R`	resistor value(s). If not specified, will use resitor values from individual iso_files. If specified, must be a named vector with Rm (m=mass) as names (e.g. `c(R45=0.3, R46=3)`), in units of `R_units`. If specified, will be used for ALL provided iso_files.
`R_units`	determined what units resistor values (`R`) are in, if they are specified. Example `R_units = "GOhm"` designates that the resistor values provided in `R` parameter are in Giga-Ohm, i.e. 10^9 Ohm.
`quiet`	whether to display (quiet=FALSE) or silence (quiet = TRUE) information messages.