LTPDA Toolbox™ contents Principles and theory   Estimate equivalent acceleration from simulation data

Tools for estimating the equivalent acceleration in LTPDA

In previous page we have discovered as the equivalent acceleration can be in principle estimated from the interferometer displacement signal. LTPDA provides a dedicated tool for the purpose. The tool name is 'ltp_ifo2acc', it is a method of the class 'ao' and it is provided with the external module 'LPF_DA_Module'. If the module is correctly installed 'ltp_ifo2acc' help can be obtained with the command 


    help ao/ltp_ifo2acc
  

  ltp_ifo2acc convert ifo data to acceleration
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
  DESCRIPTION: ltp_ifo2acc converts interferometer data to acceleration
 
 
  CALL:                 bs = ltp_ifo2acc(o1,od,pl);
                        [a1,ad] = ltp_ifo2acc(o1,od,pl);
  
 
  INPUTS:      
        - o1, channel 1 interferometer output
        - od, differential channel interferometer output
        - pl, plist containing parameters
               
  OUTPUTS:     
        - a1, Force per unit of mass on TM1 in the spacecraft reference
        frame
        - ad, Differential force per unit of mass between TMs
  
  Parameters Description
 
  REFERENCES:
 
  
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

With a click on the 'Parameters Description' link, we obtain a list of method's parameters together with a description.

In this training session we will concentrate only on 7 parameters of the full list:

LSS v4.9.2
Key Default Value Options Description
GDF 1 none thrusters actuation gain

GSUS 1 none suspension actuation gain

W1 -1.3e-06 none The parasitic stiffness per unit of mass on TM1 (s^-2)

W2 -1.9999999999999999e-06 none The parasitic stiffness per unit of mass on TM2 (s^-2)

SD1 0.0001 none Cross-talk channel 1 to diff channel

OMS DELAY O1 0.40000000000000002 none OMS processing delay on channel 1 [s]

OMS DELAY OD 0.40000000000000002 none OMS processing delay on differential channel [s]

HDF -1 none Drag-free controller model.
You can choose between 3 options:
  • -1, Uses the default builtin model ().
  • 0, calculation with Hdf will be skipped, acom1 = 0.
  • Input model, input your own model.It can be a miir, mfir, pzmodel, smodel or an ao with the commanded force
HSUS -1 none Electrostatic suspension controller model.
You can choose between 3 options:
  • -1, Uses the default builtin model ().
  • 0, calculation with Hsus will be skipped, acomD = 0.
  • Input model, input your own model.It can be a miir, mfir, pzmodel, smodel or an ao with the commanded force

In particular, parameters 'HDF' and 'HSUS' can be used to input the commanded forces to the method. The method can also calculate automatically the expected commanded forces on the basis of a built-in model for the controllers. Unfortunately, since such a model has a pole at zero, the resulting output is affected by huge transients and is not completely representative of the 'true' commanded forces provided by the control system (one should know the initial state of the DFACS to perform the correct calculation). For this reason it is always advisable to make use of the true commanded forces if available. OMS DELAY O1 and OMS DELAY OD should instead be set at 0.3 s in order to match current 'ssm' default values.

Here is a table matching current parameters names with method parameters names

Current name Method name
FEEPS_XX GDF
CAPACT_TM2_XX GSUS
IFO_X12X1 SD1
-1 * EOM_TM1_STIFF_XX W1
-1 * EOM_TM2_STIFF_XX W2


Principles and theory  Principles and theory   Estimate equivalent acceleration from simulation data Estimate equivalent acceleration from simulation data

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