design for multiple time series

Hi,

I'm working on the design of a database for time series data collected
by a variety of meteorological sensors.  Many sensors share the same
sampling scheme, but not all.  I initially thought it would be a good
idea to have a table identifying each parameter (variable) that the
sensors report on:

CREATE TABLE parameters (
    parameter_id serial PRIMARY KEY,
    parameter_name character_varying(200) NOT NULL,
    ...
)

and then store the data in a table referencing it:

CREATE TABLE series (
    record_id serial PRIMARY KEY,
    parameter_id integer REFERENCES parameters,
    reading ????
    ...
)

but of course, the data type for the parameters may vary, so it's
impossible to assign a data type to the "reading" column.  The number of
variables measured by the sensors is quite large and may grow or
decrease over time, and grouping them into subjects (tables) is not
clear, so it's not simple to just assign them to different columns.

I've been trying to search for solutions in various sources, but am
having trouble finding relevant material.  I'd appreciate any advice.

Cheers,

--
Seb