Tests performed during the heavy maintenance (2007.06.20)
Goals
Identify the origin(s) of the "acceleration" problem in MAMBO2.
- Is the acceleration problem due to a mechanical or electrical process ?
- What is the influence of the driving program on its intensity (Basic/Cascade) ?
- Any difference in the peak noise whether it is an on-off in elevation or in azimuth ?
People
Pico Veleta: DJ, SL, SN, JP
Methods
- An inclinometer was installed on the Mambo2 platform (see picture below) to measrue the vibrations during the measurements.
attachment:inclinometerPhoto.jpg
On-off measurements on an absorber. The on-off are done w/o the wobbler taking offset in azimuth and elevation to activate the Basic or Cascade controller. The Basic/Cascade limits are (600,400) arcsec in (Azimuth,Elevation). We point out that these observation are not reproducing exactly the standard bolometer observations with wobbler and a throw < 90 arcsec.
- An extra weight was added on the bolometer platform to check the effects of a change in the platform response to the vibration.
- Oscilloscope monitoring directly on Mambo2 was performed during an on-off measurements.
You can find the list of the absorber on-off scans [:AbsorberTests: here]
Results
- Inclinometer measurements for two on-off measurements with the Cascade and the Basic controller.
BR attachment:inclinometerBolo.jpg
The Basic controller leads to movements smoother than with the Cascade controller. On the bottom panels the inclinometer measurements indicate excursion on the bolometer platform about 10 times larger with the Cascade controller than with the Basic controller. BR BR
- On-off measurements with the offsets in elevation: 360" (scan 47, Cascade) and 440" (scan 50, Basic)
BR Cascade controller: scan 47 attachment:scan47-elev-cascade.jpg
Basic controller: scan 50 attachment:scan50-elev-basic.jpg
The tests showed (surprisingly?) that the peak noise was much stronger (~5-10 times) with the offsets in elevation than in azimuth. Without extra-weight on the platform the maximum peak noise reached 1 Jy in elevation, For the basic/cascade tests we used elevation offsets.BR All the measurements have shown a larger peak noise with the Cascade controller (offsets<400arcsec) than with the Basic controller. Nevertheless the peak of noise are not completely suppressed with the Basic controller but are much lower as shown on the scan 50.
- An extra weight was put on the bolometer platform (scan 51)
attachment:scan51.jpg
The add of an extra weight on the bolometer platform changed the response of that platform to the vibrations. In case of "acceleration" peak due to electrical leakage the behavior of the noise should be similar. But the scan 51 showed a peak of noise much higher (~2Jy), which seems to corroborate the the explanation of mechanical origin for the "acceleration" problem.
- Measurements of electrical peak with the oscilloscope during an on-off measurements with the offsets in elevation (scan 53).
No correlation was found between the beginning of the scans where the extra noise peaks appeared and the electric activity. A peak frequency of 5 sec was observed but which may be related to the air conditioned system. BR These measurements confirm the mechanical origin of the "acceleration" problem.