ACS Workshop, ESO Garching, 03/2004

ACS at the Atacama Pathfinder Experiment (APEX)

Dirk MudersMax-Planck-Institutfür Radioastronomie

Bonn

ACS Workshop, ESO Garching, 03/2004

The APEX Project

● APEX is a 12m radio telescope located north of the ALMA site on Chajnantor at 5100m

● APEX is a pathfinder mission aimed at exploring the southern sub-mm sky in preparation for ALMA

● APEX is a collaboration between MPIfR, AIRUB, ESO and OSO

ACS Workshop, ESO Garching, 03/2004

The APEX Project (cont.)

● APEX is a copy of the US ALMA prototype antenna built by VERTEX

● Compared to the ALMA telescope APEX features two additional Nasmyth receiver cabins, an instrument container and a compressor platform

ACS Workshop, ESO Garching, 03/2004

APEX Interfaces

● APEX uses the same vendor-supplied control computers (ACU & PTC) and the same CAN bus interface (ICD 9) like ALMA

● It was thus decided to re-use the ALMA prototype telescope control software (TICS) and most of the corresponding control hardware setup

ACS Workshop, ESO Garching, 03/2004

APEX Instrumentation

● The APEX instrumentation will consist of:

– Bolometer cameras with several hundred pixels (e.g. LABOCA) at λ=1 mm to 350 μm

– Heterodyne receivers (single-pixel and arrays) at ν=230 GHz to 1.5 THz (200 μm)

– Continuum backends

– Auto-Correlators

ACS Workshop, ESO Garching, 03/2004

APEX Status

● APEX has been erected in early 2003

● In September 2003 the telescope control system hard- and software were installed

● Preliminary acceptance tests took place in November 2003

● Currently the pointing is being checked with an optical telescope

ACS Workshop, ESO Garching, 03/2004

ACS Workshop, ESO Garching, 03/2004

Difficulties at 5000m:Low pressureLow oxygen content

Oxygenization

Pressurized HardDriveBox

ACS Workshop, ESO Garching, 03/2004

ACS / TICS at APEX

● APEX is using TICS and thus ACS

● The ACS version in use is determined by TICS (currently ACS 2.0.1)

● We will probably upgrade to ACS 3.0.1 this year if a new (stable) TICS port will be available

ACS Workshop, ESO Garching, 03/2004

ACS / TICS at APEX (cont.)

● TICS provides antenna control (astronomical coordinate tracking, patterns, CAN bus access, etc.) via 4 COBs

● ALMA's timing setup is much more complicated than needed for APEX

● APEX uses GPS & IRIG-B to slave the ABM to TAI and a hardware timing generator for the 48ms Timing Events

ACS Workshop, ESO Garching, 03/2004

APEX Instrument Interfaces

● APEX instrumentation needs to be interfaced to the ACS -> make components

● Many instruments are legacy devices that use a simple ASCII protocol over a socket rather than the CAN bus that ALMA employs

● Thus a socket DevIO implementation is needed

ACS Workshop, ESO Garching, 03/2004

APEX Socket DevIO

● The socket code needs to handle sending and parsing ASCII messages for component properties AND for methods

● It must handle multiplexing and concurrent accesses to the component properties

● The messages are standardized using the SCPI syntax

ACS Workshop, ESO Garching, 03/2004

Socket DevIO Class Diagram

ACS Workshop, ESO Garching, 03/2004

SCPI Syntax

Component sends the device:

[APEX:]<device name>:<property/method name>?

The device replies:

[APEX:]<device name>:<property/method name> <value> \ <ISO 8601 time stamp>

Example:

APEX:SIS345:LO2:MULTI1:backShort2?

APEX:SIS345:LO2:MULTI1:backShort2 2.341 \ 2003-11-05T10:19:38.310+00.00

ACS Workshop, ESO Garching, 03/2004

APEX Instruments IDLs

● The instrument IDLs are kept as generic as possible to be able to re-use them for new instruments of the same kind; only a new CDB entry is needed

● Instruments are implemented via a hierarchical device tree to:

– have one high-level interface for observing

– have low-level interface(s) for engineering

ACS Workshop, ESO Garching, 03/2004

APEX Device HierarchyAPEX:SIS345 apexHFE.idlAPEX:SIS345:CALUNIT apexHFE_HCal.idlAPEX:SIS345:MIXER1 apexHFE_Mixer.idlAPEX:SIS345:MIXER1:COLDAMP apexHFE_ColdAmp.idlAPEX:SIS345:MIXER2 apexHFE_Mixer.idlAPEX:SIS345:MIXER2:COLDAMP apexHFE_ColdAmp.idlAPEX:SIS345:LO1 apexHFE_LO.idlAPEX:SIS345:LO1:GUNN apexHFE_Gunn.idlAPEX:SIS345:LO1:PLL apexHFE_PLL.idlAPEX:SIS345:LO1:MULTI1 apexHFE_Multi.idlAPEX:SIS345:LO1:MULTI2 apexHFE_Multi.idlAPEX:SIS345:LO2 apexHFE_LO.idlAPEX:SIS345:LO2:GUNN apexHFE_Gunn.idlAPEX:SIS345:LO2:PLL apexHFE_PLL.idlAPEX:SIS345:LO2:MULTI1 apexHFE_Multi.idlAPEX:SIS345:LO2:MULTI2 apexHFE_Multi.idl

ACS Workshop, ESO Garching, 03/2004

Code generation● The C++ component code is automatically

generated from the IDLs using a modified version of the “bdsGenerator” from AIRUB

● C++, *.h, xml and xsd files are created

● DevIOUDPSock socket communication code & SCPI commands are automatically added

● Embedded system host name and port are stored in the CDB and read at startup

ACS Workshop, ESO Garching, 03/2004

Serial & GPIB Devices● Many commercial devices use RS232 or

GPIB communication with given commands

● General problem of non-concurrent access -> need to serialize commands

● Demultiplexing is done in the standalone SCPI command parser (CID) which in turn talks to the hardware, i.e. CID is a “driver”

● Socket DevIO is re-used here

ACS Workshop, ESO Garching, 03/2004

CID Setup

ACS Workshop, ESO Garching, 03/2004

Device Emulators

● A simple Python script was developed to emulate socket devices

● The emulator uses the IDLs and sets up all property types automatically

● Simple funtionality such as setting actual to commanded values is included

● Can be extended easily

ACS Workshop, ESO Garching, 03/2004

APEX Control System (APECS)

● For real observations all those components need to be set up and coordinated to perform “scans”. This is done by the “APEX Observing Engine”

● The APEX raw data format (MBFITS) was defined based on ALMA's TI-FITS

● The raw data writer collects telescope and backend data to write MBFITS files

ACS Workshop, ESO Garching, 03/2004

APECS (cont.)

● APECS uses ACS to provide the necessary infrastructure to observe with APEX:

– Observer CLI & GUI to set up scans for a number of standard observing modes

– Telescope control (via TICS) & device setup

– Raw data (MBFITS) writing

– Online calibration (TA*) and data reduction for

pointing, focus and skydip

ACS Workshop, ESO Garching, 03/2004

APECS Class Diagram

ACS Workshop, ESO Garching, 03/2004

APECS Deployment

Diagram

ACS Workshop, ESO Garching, 03/2004

ACS Pros

● Hides many CORBA details

● Allows for flexible distributed systems

● Simple deployment reconfiguration

● Component property model is very useful for hardware device implementations

● Remote monitoring and remote observing is easily implemented

ACS Workshop, ESO Garching, 03/2004

ACS Cons

● Steep learning curve; lab staff typically does not want to deal with it directly

● ACS is pretty large; this conflicts with using it in embedded systems

● TCP connections get stuck when parts of the software need to be restarted

● Missing connection to existing lab tools such as LabView

ACS Workshop, ESO Garching, 03/2004

APEX's ACS Wishlist

● Auto-reconnection does not always work but is essential for operations

● Rather get a stable and debugged ACS than new features since ACS is the infrastructure for everything else

● Share IDL and naming structure with other projects to facilitate re-using code