Devices (High-level interface)

What is a Device?

The high-level interface of Autolab is an abstraction layer of its low-level interface, which allows easy and safe communication with laboratory instruments without knowing the structure of their associated Driver.

In this approach, an instrument is fully described with a hierarchy of three particular Elements: the Modules, the Variables and the Actions.

• A Module is an Element that consists in a group of Variables, Actions, and sub-Modules. The top-level Module of an instrument is called a Device.

• A Variable is an Element that refers to a physical quantity, whose value can be either set and/or read from an instrument (wavelength of an optical source, position of a linear stage, optical power measured with a power meter, spectrum measured with a spectrometer…). Depending on the nature of the physical quantity, it may have a unit.

• An Action is an Element that refers to a particular operation that can be performed by an instrument. (homing of a linear stage, zeroing of a power meter, acquisition of a spectrum with a spectrometer, etc.). An Action may have a parameter.

The Device of a simple instrument is usually represented by only one Module, and a few Variables and Actions attached to it.

-- Tunics (Module/Device)
        |-- Wavelength (Variable)
        |-- Output state (Variable)

Some instruments are a bit more complex, in the sense that they can host several different modules. Their representation in this interface generally consists of one top level Module (the frame) and several others sub-Modules containing the Variables and Actions of each associated module.

-- XPS Controller (Module/Device)
        |-- ND Filter (Module)
                |-- Angle (Variable)
                |-- Transmission (Variable)
                |-- Homing (Action)
        |-- Linear stage (Module)
                |-- Position (Variable)
                |-- Homing (Action)

This hierarchy of Elements is implemented for each instrument in its driver files, and is thus ready to use.

Load and close a Device

The procedure to load a Device is almost the same as for the Driver, but with the get_device function. You need to provide the nickname of a driver defined in the devices_config.ini (see Local configuration).

>>> lightSource = autolab.get_device('my_tunics')

Note

You can temporarily overwrite some of the parameters values of a configuration by simply providing them as keywords arguments in the get_device function:

>>> laserSource = autolab.get_device('my_tunics', address='GPIB::9::INSTR')

To properly close the connection to the instrument, simply call the close function of the Device. This object will no longer be usable.

>>> lightSource.close()

To close the connection to all instruments (devices, not drivers) at once, you can use Autolab’s close function.

>>> autolab.close()

Navigation and help in a Device

Navigation in the hierarchy of Elements of a given Device is based on relative attributes. For instance, to access the Variable wavelength of the Module (Device) my_tunics, simply execute the following command:

>>> lightSource.wavelength

In the case of a more complex Device, for instance a power meter named my_power_meter that has several channels, you can access the Variable power of the first channel channel1 with the following command:

>>> powerMeter = autolab.get_device('my_power_meter')
>>> powerMeter.channel1.power

Every Element in Autolab is provided with a help function that can be called to obtain some information about it, but also to know which further Elements can be accessed through it, in the case of a Module. For a Variable, it will display its read and/or write functions (from the driver), its Python type, and its unit if provided in the driver. For an Action, il will display the associated function in the driver, and its parameter (Python type and unit) if it has one. You can also print() the object to display this help.

>>> lightSource.help()
>>> print(lightSource.wavelength)
>>> powerMeter.help()
>>> print(powerMeter.channel1)
>>> powerMeter.channel1.power.help()

Use a Variable

If a Variable is readable (read function provided in the driver), its current value can be read by calling its attribute:

>>> lightSource.wavelength()
1550.55
>>> lightSource.output()
False

If a Variable is writable (write function provided in the driver), its current value can be set by calling its attribute with the desired value:

>>> lightSource.wavelength(1549)
>>> lightSource.output(True)

To save the value of a readable Variable locally, use its save function with the path of the desired output directory (default filename), or file:

>>> lightSource.wavelength.save('.\mesures\')
>>> lightSource.wavelength.save('.\mesures\power.txt')

Use an Action

You can execute an Action simply by calling its attribute:

>>> linearStage = autolab.get_device('my_linear_stage')
>>> linearStage.goHome()

Script example

With all these commands, you can now create your own Python script. Here is an example of a script that sweeps the wavelength of a light source, and measures the power of a power meter:

# Import the package
import autolab
import pandas as pd

# Open the Devices
myTunics = autolab.get_device('my_tunics')
myPowerMeter = autolab.get_device('my_power_meter')

# Turn on the light source
myTunics.output(True)

# Sweep its wavelength and measure a power with a power meter
df = pd.DataFrame()
step = 0.01
start = 1550
stop = 1560
points = int(1 + (stop - start)/step)
for wl in np.linspace(start, stop, points):

    # Set the parameter
    myTunics.wavelength(wl)

    # Measures the values
    wl_measured = myTunics.wavelength()
    power = myPowerMeter.line1.power()

    # Store the values in a list
        df = df.append({'wl_measured': wl_measured, 'power': power}, ignore_index=True)

# Turn off the light source
myTunics.output(False)

# Close the Devices
myTunics.close()
myPowerMeter.close()
# Or use autolab.close()

# Save data
df.to_csv('data.csv')