You are here: NRAO Public Wiki>Main Web>TWikiUsers>ToneyMinter>GBTBalancingProject (2007-10-05, ToneyMinter) Edit wiki text Edit Attach Print version

Welcome To The NEW Balancing Project Web Page

Project Charter

Project Timeline

  • DONE Develope BalanceOnOff() function by September 15
  • DONE Develope ChangeAttenuation() function by September 15
  • DONE Test functions using the GBT by September 24
  • DONE Modifications from testing done by Septemnber 30
  • DONE Code reviewed by Software Group by September 30
  • DONE Documentation for new functions written by September 30
  • DONE Code given to Software Group for release with Astrid by October 3

Project Summary Report NEW

Notes

  • no MRs will be needed for this project
  • The project received approval on August 20 with prelimonary completion time set for the end of September.
  • The code for the functions will be given to the software group. They will put the functions under version control. The functions will be made available as observing directives under astrid.
  • GBT test time will be on September 13, 2007 from 21:00 - 24:00
  • BalanceOnOff and ChangeAttenuation were made astrid observing directives by M. Clark

Test Results

The first several attempts to use BalanceOnOff did not all work properly. There was a problem with a few small typos that were quickly fixed. Also, it was found that not all attenuators would get changed on the first attempt. This is likely due to there being an "active" that happens automatically after each attenuator is set. This was overcome by setting the values twice in a script. I also had the wrong names for the Converter Rack attenuators - a problem that was quickly fixed.

Once the problems were overcome, things went smoothly. By watching the IF Rack power sampler cleo chart recorders I could see that things were behaving properly.

OnOff (or OffOn) observations were made of 3C 286, Cygnus A and 3C 48. I would do a OnOff after using the new BalanceOnOff() function. Then I would balance the system off the source and perform an OffOn observations. Finally I would balance on the source and perform and OnOff observations. It is clearly evident from the data that using the BalanceOnOff() function creates a situation were you get better baseline structure - if you don't saturate the system as Cygnus A can with wide bandwidths.

I also found that it is better to balance on the source and then move off the source to figure out the new attenutation settings. For wide bandwidths and very strong sources, if you balance on source and then move on source you can saturate the samplers. Doing things the other way can make the power levels go to zero but the resulting attenuation change is nearer to what you would desire in this case.

The Functions

* BalanceOnOff.py.txt: The BalanceOnOff() function code

* ChangeAttenuation.py.txt: The ChangeAttenuation() function code

* BalConvRack.py.txt

* SetConverterRackAttenuation.py.txt

Documentation

When there is a large difference in power received by the GBT between two positions on the sky, it is advantageous to balance the IF system power levels to be at the mid-point of the two power levels. Typically this is needed when the "source position" is a strong continuum source. A simple Astrid Scan Type, BalanceOnOff(), has been created to handle this senario. BalanceOnOff() slews to the source position and then balances the IF system. It then determines the power levels that are observed in the IF Rack. Then the telescope is slewed to the off position and the power levels are determined again. The change in the power levels is then used to determine attenuator settings that put the balance near the mid-point of the observed power range. Note that the balance is determined only to within +/- 0.5 dB owing to the integer settings of the IF Rack attenuators.

In some cases it might be desirable if the observer can "manually" change all the attenuator settings in the IR Rack or the Converter Rack by the same amount. The function ChangeAttenuation() allows the observer to do this.

  • BalanceOnOff(SourceName,Offset)
BalanceOnOff() takes two arguments. The first is SourceName which is a string containing the name of the source. The source name should exactly match the name of a source in your source Catalog. The second argument, Offset, is an Offset that determines where the off position for determining the balancing point is reltative to the source position.

  • ChangeAttenuation(DeviceName, AttenuationChange)
ChangeAttenuation takes two arguments. The first is DeviceName, which is a string that can be either "IFRack" or "ConverterRack". This specifices the device in which the attenuators will be changed. The second argument is ,noop>AttenuationChange, a float. This specifies how much the attenuators should be changed. This value can be both positive or negative.

It should be noted that if any new attenuator setting is less than zero or exceeds the maximum value, 31 for the IF Rack and 31.875 for the Converter Rack, then the attenuator settings is made to be the appropriate limiting value.

There are two more useful astrid scripts:

This function balances the specified Converter Rack modules to the requested voltage. To use this function you would use the following in your astrid script:

execfile("/users/tminter/astrid/BalConvRack.py")
BalConvRack( module_list, target_values)

where "module_list" is an array with a list of converter module numbers and "target_values" is a corresponding array with a list of RF values. For example if one wants to adjust CM1 to an RF value of 2.5, and CM5 to 3.5, then one says:

BalConvRack( [1,5], [2.5, 3.5] )

This adjusts the converter module attenuators such that the target power levels are attained, to within a threshhold of 0.15 volts as read by the RF power samplers.

A python function which you can use that sets all the attenuators in the Converter Rack with the same amount of attenuation. This would replace the 16 "SetValue" commands that I gave you earlier. The two lines of code are

execfile("/users/tminter/astrid/SetConverterRackAttenuation.py")
SetConverterRackAttenuation(15.)

The first line lets you use the function and the second line is a call to the function to set all the Converter Rack attenuators to 15 dB.

--Main.ToneyMinter - 20 Aug 2007

Topic attachments
I Attachment Action Size Date Who Comment
BalConvRack.py.txttxt BalConvRack.py.txt manage 3 K 2007-10-05 - 13:57 ToneyMinter  
Balance.configconfig Balance.config manage 1 K 2007-09-14 - 13:45 ToneyMinter Configuration file used for tests
BalanceOnOff.py.txttxt BalanceOnOff.py.txt manage 6 K 2007-09-14 - 14:52 ToneyMinter The BalanceOnOff() function code
BalanceTest.py.txttxt BalanceTest.py.txt manage 809 bytes 2007-09-14 - 13:44 ToneyMinter Example astrid script for tests
ChangeAttenuation.py.txttxt ChangeAttenuation.py.txt manage 4 K 2007-09-14 - 14:53 ToneyMinter The ChangeAttenuation() function code
SetConverterRackAttenuation.py.txttxt SetConverterRackAttenuation.py.txt manage 957 bytes 2007-10-05 - 13:58 ToneyMinter  
balancetest.astrid.loglog balancetest.astrid.log manage 140 K 2007-09-14 - 13:42 ToneyMinter Atrid log from balancing tests on the GBT
Edit  | Attach | Print version | History: r13 < r12 < r11 < r10 | Backlinks | View wiki text | Edit wiki text | More topic actions
Topic revision: r12 - 2007-10-05, ToneyMinter
This site is powered by FoswikiCopyright © by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding NRAO Public Wiki? Send feedback