The ps120 module

Basic drivers for an Oxford Instruments model PS120 power supply

Note that this module does not represent an Instrument subclass, since the PS120 is never used by itself—it is always part of a larger system driving both a magnet power supply and temperature controllers, and the power supply cannot usually be used in isolation.

Classes

PS120

class src.instruments.noauto.ps120.PS120(name='Magnet', protocol='ISOBUS', isobusAddress='0', visaAddress='GPIB0::23', serialConfig=None)

This is a basic driver for an Oxford Instruments model PS120 power supply. It should be included in an Instrument class representing a cryostat-magnet system.

Parameters :

name : str

A name to identify the instrument.

protocol : {‘ISOBUS’, ‘GPIB’, ‘Serial’, ‘Gateway Master’, ‘Gateway Slave’}

The protocol for communication between the computer and the temperature controller.

isobusAddress : str

An integer string representing the ISOBUS address, if relevant. An integer will be accepted and converted.

visaAddress : str

A full VISA resource address (including the bus) to locate the instrument (e.g. “GPIB0::27”).

serialConfig : dict

A dictionary to indicate how to configure a serial port, which is used with both the ‘ISOBUS’ and ‘Serial’ protocols.

Methods

getActivity()

Get the activity status.

Returns :

str :

An integer contained in a string representing the current activity status. The recognized values are these:

• 0: Hold at current field,
• 1: Ramp the field to the setpoint,
• 2: Ramp the field to zero, and
• 4: Clamp the output.

getField()

Return the magnetic field in Tesla.

Returns :

float :

The magnetic field in Tesla.

getFieldSetpoint()

Return the field setpoint in Tesla.

Returns :

float :

The magnetic field setpoint in Tesla.

getStatus()

Update the power supply status.

Read the power supply status, and update the local polarity variables to reflect this change.

Returns :

dict :

The status dictionary, containing the following items: ‘system_status_1’, ‘system_status_2’, ‘activity’, ‘control_mode’, ‘switch_heater’, ‘mode_1’, ‘mode_2’, ‘polarity_1’, and ‘polarity_2’. The meanings are described in the Notes section.

Notes

The power supply returns a string of the form XmnAnCnHnMmnPmn. The meanings and values of the parts of this are described here.

Xmn: System status

m: Status 1

• 0: Normal
• 1: Quenched
• 2: Over-heated
• 4: Warming up

n: Status 2

• 0: Normal
• 1: On positive voltage limit
• 2: On negative voltage limit
• 4: Outside negative current limit
• 8: Outside positive current limit

An: Activity

• 0: Hold
• 1: To setpoint
• 2: To zero
• 4: Output clamped

Cn: Control status

• 0: Local and locked
• 1: Remote and locked
• 2: Local and unlocked
• 3: Remote and unlocked
• 4: Auto-run-down
• 5: Auto-run-down
• 6: Auto-run-down
• 7: Auto-run-down

Hn: Switch heater status

• 0: Off—magnet at zero (switch closed)
• 1: On (switch open)
• 2: Off—magnet at field (switch closed)
• 8: No switch fitted

Mmn: Mode

m: Mode 1

• 0: Amps, Immediate, Fast
• 1: Tesla, Immediate, Fast
• 2: Amps, Sweep, Fast
• 3: Tesla, Sweep, Fast
• 4: Amps, Immediate, Train
• 5: Tesla, Immediate, Train
• 6: Amps, Sweep, Train
• 7: Tesla, Sweep, Train

n: Mode 2

• 0: At rest (output constant)
• 1: Sweeping (output changing)
• 2: Rate limiting (output changing)
• 3: Sweeping and rate limiting (output changing)

Pmn: Polarity

m: Polarity 1 (see below)

• 0: pos, pos, pos
• 1: pos, pos, neg
• 2: pos, neg, pos
• 3: pos, neg, neg
• 4: neg, pos, pos
• 5: neg, pos, neg
• 6: neg, neg, pos
• 7: neg, neg, neg

n: Polarity 2

• 0: Output clamped (transition)
• 1: Forward (verification)
• 2: Reverse (verification)
• 4: Output clamped (requested)

The Polarity 1 value actually contains the values of three separate polarities: desired, magnet, and commanded (in order). “pos” represents forward polarity, and “neg” means reverse polarity. The three values are defined to be

• “desired”: the final or target polarity (polarity of the setpoint current)
• “magnet”: the polarity of the power supply last time the magnet was left persistent
• “commanded”: the present polarity of the power supply unless the output is clamped

getSweepRate()

Return the field sweep rate in Tesla/min.

Returns :

float :

The magnetic field sweep rate in Tesla/min.

initialize()

Prepare the power supply for use.

Prepare the power supply for use by

1. opening the appropriate communication channel;
2. setting the control mode to ‘remote and unlocked’;
3. setting the activity to ‘hold’;
4. setting the polarity to ‘forward’;
5. setting the sweep rate to 0.5 T/min;
6. setting the sweep mode to its default (Tesla, auto, unaffected); and
7. setting the switch heater to ‘Off, magnet at zero’.

setActivity(activity='0')

Set the activity mode of the power supply.

Parameters :

activity : str

An integer string representing the desired activity. The accepted values are listed below.

• ‘0’: Hold at current field (default).
• ‘1’: Ramp the field to the setpoint.
• ‘2’: Ramp the field to zero.
• ‘4’: Clamp the output.

setControlMode(controlMode='3')

Set the control mode for the power supply.

Parameters :

controlMode : str, optional

An integer string representing the desired control mode. Allowed values are the following.

• ‘0’: Local and locked (power-up state).
• ‘1’: Remote and locked.
• ‘2’: Local and unlocked.
• ‘3’: Remote and unlocked (default).

setField(field)

Set the magnetic field in Tesla.

Parameters :

field : float

The magnetic field setpoint in Tesla.

setPolarity(polarity='0')

Set the power supply polarity.

Parameters :

polarity : str

A string containing a single integer representing the desired polarity (or polarity-changing action). The following values are accepted.

• ‘0’: Do nothing (default).
• ‘1’: Set the polarity to forward.
• ‘2’: Set the polarity to reverse.
• ‘4’: Swap the polarity.

setSweepMode(sweepMode='9')

Set the power supply’s sweep mode.

The power supply’s sweep mode consists of three parameters:

Display:

The instrument’s front-panel display units (amps or tesla)

Mode:

Either “immediate” or “sweep”; in “immediate” mode, the power supply ramps current at its maximum allowed value, while in “sweep” mode, the power supply uses a user-specified sweep rate

Magnet sweep:

One of two user-defined sweep profiles: “fast” and “train”; the “fast” mode is entered upon power supply startup

Parameters :

sweepMode : str, optional

The integer string code to specify the sweep mode of the power supply. The allowed codes are the following.

• ‘0’: Amps, Immediate, Fast
• ‘1’: Tesla, Immediate, Fast
• ‘2’: Amps, Sweep, Fast
• ‘3’: Tesla, Sweep, Fast
• ‘4’: Amps, Immediate, Train
• ‘5’: Tesla, Immediate, Train
• ‘6’: Amps, Sweep, Train
• ‘7’: Tesla, Sweep, Train
• ‘8’: Amps, Auto, Unaffected
• ‘9’: Tesla, Auto, Unaffected (default)

setSweepRate(sweepRate=0.5)

Set the magnetic field sweep rate in Tesla/min.

Parameters :

sweepRate : float, optional

The desired sweep rate for the magnet in Tesla/min (default 0.5).

setSwitchHeater(heaterStatus='0', delay=20.0)

Set the status of the switch heater.

Turn the switch heater on or off, optionally checking whether it is safe to do so. Then wait a specified amount of time for the power supply to carry out the command.

Parameters :

heaterStatus : {‘0’, ‘1’, ‘2’}, optional

An integer string representing the desired switch heater status. The following values are accepted.

• ‘0’: Turn the heater off (default).
• ‘1’: Turn the heater on if the power supply current and the magnet current are equal. Otherwise, do nothing.
• ‘2’: Turn the heater on without checking the currents.

delay : float, optional

The time to wait (in seconds) after commanding the switch heater to adopt the specified status. The value should be at least 15s.