Several LHO ISI T240s should have their masses centered.

Posted in SEI log 911.  Repeated here verbatum:

LLO lost lock Christmas Eve: LLO aLog 23821.  They found railing T240s and centering the T240 masses solved the issue.  Stuart emailed me and set me down my current hole.  Most of the things I found down there I knew before but I still appreciate the reminder and I learned a few things on the way back out.

Yes the T240 Mass Positions are monitored, for example:

Slow: H1:ISI-ETMX_T240MON_U1_INMON
Fast: H1:ISI-ETMX_T240MON_U1_IN1 (4k tp)

These are counts with a calibration of   20V/2^16cts/2

The second divide 2 is from the 2x gain in the T240 Interface chassis (still waiting for Ben to confirm this interpretation.)

Here is a snip from the T240 operations manual:

• If the values are outside the ±3.5 V range the sensor may not be able to report seismic signals properly. For this condition, mass centring must be done.

• If the values are within the range ±3.5 V but not within ±2 V range the sensor is sufficiently centred that it will report seismic signals properly. However, it is strongly recommended the masses be recentred.

• If the values are within the range ±2 V but not within the ±0.3 V range the sensor is sufficiently centred that it will report seismic signals properly. However, the closer the mass positions are to 0 V, the more room there is to tolerate further ambient temperature changes. For this condition, centring the masses is recommended if it is convenient to do so.

• If the mass positions are all within the range ±0.3 V there is no need to recentre, although it can be done if desired

So here more may be less in that too many options make decisions harder.  Given what we are doing, it makes sense though, that we require the T240 to stay within the +- 0.3V which is much tighter than the STS2 centering voltage limits: +-2.0 or 1.5V (depending on the manual source.)  The output voltage range for the T240 and the STS2 are respectively +- 4.5 and 10.0 volts.

Kissel made a script for the STS2 and I've modified it to work for the IFOs ISI T240s.  It is found in /opt/rtcds/userapps/release/isi/common/scripts.  This is commited to the svn r12384.  Here is the output for H1:

scripts 0$ ./check_T240_centering.py H1
Averaging Mass Centering channels for 10 [sec] ...


There are 19 T240 proof masses out of range ( > 0.3 [V] )!
ETMX T240 2 DOF X/U = -1.95 [V]
ETMX T240 2 DOF Y/V = -2.184 [V]
ETMX T240 2 DOF Z/W = -1.098 [V]
ITMX T240 1 DOF X/U = -3.175 [V]
ITMX T240 1 DOF Z/W = 0.474 [V]
ITMX T240 2 DOF Y/V = 0.576 [V]
ITMX T240 3 DOF X/U = -3.158 [V]
ITMY T240 1 DOF X/U = -0.396 [V]
ITMY T240 1 DOF Y/V = 0.38 [V]
ITMY T240 1 DOF Z/W = 0.366 [V]
ITMY T240 2 DOF Y/V = 0.445 [V]
ITMY T240 2 DOF Z/W = -0.31 [V]
ITMY T240 3 DOF X/U = -0.861 [V]
ITMY T240 3 DOF Z/W = -3.168 [V]
BS T240 1 DOF Y/V = 0.951 [V]
BS T240 1 DOF Z/W = 0.427 [V]
BS T240 2 DOF X/U = 1.008 [V]
BS T240 2 DOF Z/W = 0.509 [V]
BS T240 3 DOF Z/W = 0.983 [V]


All other proof masses are within range ( < 0.3 [V] ):
ETMX T240 1 DOF X/U = 0.13 [V]
ETMX T240 1 DOF Y/V = 0.103 [V]
ETMX T240 1 DOF Z/W = 0.125 [V]
ETMX T240 3 DOF X/U = 0.099 [V]
ETMX T240 3 DOF Y/V = 0.094 [V]
ETMX T240 3 DOF Z/W = 0.071 [V]
ETMY T240 1 DOF X/U = 0.139 [V]
ETMY T240 1 DOF Y/V = 0.101 [V]
ETMY T240 1 DOF Z/W = 0.151 [V]
ETMY T240 2 DOF X/U = -0.058 [V]
ETMY T240 2 DOF Y/V = 0.134 [V]
ETMY T240 2 DOF Z/W = 0.175 [V]
ETMY T240 3 DOF X/U = 0.162 [V]
ETMY T240 3 DOF Y/V = 0.124 [V]
ETMY T240 3 DOF Z/W = 0.244 [V]
ITMX T240 1 DOF Y/V = -0.092 [V]
ITMX T240 2 DOF X/U = -0.163 [V]
ITMX T240 2 DOF Z/W = 0.261 [V]
ITMX T240 3 DOF Y/V = 0.214 [V]
ITMX T240 3 DOF Z/W = -0.293 [V]
ITMY T240 2 DOF X/U = 0.227 [V]
ITMY T240 3 DOF Y/V = -0.293 [V]
BS T240 1 DOF X/U = 0.232 [V]
BS T240 2 DOF Y/V = 0.236 [V]
BS T240 3 DOF X/U = 0.137 [V]
BS T240 3 DOF Y/V = 0.256 [V]


Assessment complete.
hugh.radkins@opsws8:scripts

So while most of the units out of 'range' are less than 1 volt, there are three masses at greater than 3volts.  And no, LHO has not been monitoring these--thanks to Stuart for the prod to look closer.

Additionally, trekking to the CER is not required for centering.  The X bank of the T240INF has an AutoZ (FM6) tied to the Binary Out for centering.

Again from the manual:

How to initiate mass centring

You can initiate mass centring using either of these two methods:

Pull the MC/RX pin high for at least 1 second (referenced to DGND)

The other method is through RS232.  The 1 second duration is the thing I wanted to highlight.

Attached are the mass positions for H1 ETMX T240s for 60 days.  Very interesting...seven of the nine masses are wandering about +-200counts and the path is very similar, likely the temperature affect.  The other two masses though (same T240) are masking most of the temperature swings with a 3000 count drift.  Don't know what this tells me other than "please center me."