Calibration of housekeeping parameters

One of the duty of the electronic boards used by Strip is to measure instrument parameters like currents, voltages, temperatures, etc. These parameters are called housekeepings and are vital to monitor the status of the instrument. Like scientific samples, housekeeping parameters are measured by digital units and are stored as integer numbers, nicknamed ADU (analog-to-digital unit). Calibration curves must be applied to ADU numbers to retrieve a physically meaningful unit (e.g., milliampere, Kelvin, etc.). These calibration curves are provided in the form of Excel spreadsheets, and striptease provides a few utilities to ease the conversion between ADUs and physical units.

Usage of calibration tables

The most basic functions to apply calibration tables are provided by the class CalibrationTables. This class implements two methods, named physical_units_to_adu() and adu_to_physical_units(), which perform the two conversions:

from calibration import CalibrationTables

cal = CalibrationTables()
print(cal.physical_units_to_adu(
    polarimeter="R0",
    hk="idrain",
    component="HA1",
    value=1000,
))

A CalibrationTable object connects with the server when the constructor is called, because it needs to know which is the association between the board name (in the example above, R) and the board number used by the electronics. Once the object cal has been constructed, the connection is no longer used. If you have already instanced a Config object, you can pass it to the constructor and it will be reused:

from calibration import CalibrationTables
from config import Config
from striptease import StripConnection

conn = StripConnection()
conn.login()

config = Config()
config.load(conn)

# Use "conn" and "config"
# …

# Reuse the configuration object
cal = CalibrationTables(config)

class calibration.CalibrationTables(config=None)

Calibration tables used to convert HK ADUs into physical units and back

This class loads the calibration tables for housekeeping parameters from a set of Excel files.

You can pass a striptease.Config class to this class. Not doing so is equivalent to the following code:

from calibration import CalibrationTables
from config import Config
from striptease import StripConnection

with StripConnection() as conn:
    conf = Config()
    conf.load(conn)

cal_tables = CalibrationTables(conf)

adu_to_physical_units(polarimeter, hk, component, value)

Convert ADUs into physical units for an housekeeping parameter.

The meaning of the parameters polarimeter, hk, and component is the same as in get_calibration_curve().

get_calibration_curve(polarimeter, hk, component)

Return a CalibrationCurve object for an housekeeping parameter

Parameters:

• polarimeter (str) – the name of the polarimeter, e.g., I4 or W3
• hk (str) –

  one of the following strings:

  • vdrain: drain voltage
  • idrain: drain current
  • vgate: gate voltage
  • vphsw: voltage pin for a phase switch
  • iphsw: current pin for a phase switch
• component (str) – name of the component within the polarimeter. For LNAs, you can use whatever string works with striptease.get_lna_num(). For phase switches, you must pass an integer number in the range 0…3.

Returns:

A CalibrationCurve object.

physical_units_to_adu(polarimeter, hk, component, value)

Convert physical units into ADUs for an housekeeping parameter.

The meaning of the parameters polarimeter, hk, and component is the same as in get_calibration_curve().

Low-level calibration functions

A calibration curve is stored in a CalibrationCurve object, which has the following fields:

1. slope (float)
2. intercept (float)
3. mul (int)
4. div (int)
5. add (int)

The operation carried out by the electronics to convert physical units to ADU is the following (integer operations):

adu = value * mul / div + add

However, Striptease uses the following floating-point operation:

adu = int(value * slope + intercept)

These operations are implemented by the functions calibration.physical_units_to_adu() and calibration.adu_to_physical_units(), which require a CalibrationCurve object.

class calibration.CalibrationCurve(slope, intercept, mul, div, add)

Linear calibration curve (from physical units to ADU) for an housekeeping parameter.

slope

Floating-point value for the slope of the calibration curve

intercept

Floating-point value for the additive offset of the calibration curve

mul

Integer numerator of the slope of the calibration curve

div

Integer denominator of the slope of the calibration curve

add

Integer value for the additive offset of the calibration curve