Monitoring the aux cables and towers.

27oct20

Links:
    Intro
        Photo showing how strain and temp sensors are mounted

    Acquiring the data

manuals

The cable temperature data

Plot the aux cable temperature data vs date, hour (.ps) (.pdf)

Tower 8 and tower12 temperature oscillations (.ps) (.pdf)

Histogram of cable temps shows dropouts every .5 degF above 80F(.ps) (.pdf)

Rate of change of temp vs hour of day (.ps) (.pdf)

The tower tilt data

Plotting the tower tilts vs date and hour of day (.ps) (.pdf)

Plotting the radial tower tilts vs the (main-backstay) cable temperature differences (.ps) (.pdf)

The strain gauge differences at each aux socket

Summary of things to look into.

Notation:

main cable: from tower to platform. also called platform cable.
backstay cable: from tower to anchor.
aux cable: installed 1995 during gregorian upgrade to support the added weight.

aux main. 2 cables from each tower connect to the platform about 60 feet from the farther platform corners
aux backstay: 2 cable from each anchor to up and connect to the top of the tower.

Updates:

02nov20: updated to data through 31oct20

Intro

WJE installed monitoring equipment on the 305 meter telescope on 12oct20. As of 27oct20 they are monitoring:

Cable temperatures:

At the towers:

auxmain cables
auxbackstay cables

At the anchors: (as of 27oct20 data not yet available for download)

T12 backstay auxcable west
T4 backstays auxcable north

Tilt sensors:

At the towers

tilt sensor aligned with the radial direction of the cables
tilt sensor aligned perpendicular to the radial direction

Strain measurements

vibrating wire strain gauges
At the towers:

2 strain gauges are connected on each side (horizontal) of each aux cable socket

to measure cable slippage from socket:

lvdt connected between cable socket and cable

T12 aux backstay west
T4 aux backstay north

Photo showing temp sensors and strain gauges mounting (.jpg)

this is on top of tower 8. You see the platform aux cables. The drone is in the south looking north

The closest cable is T8platformaux south

The aluminum tape is covering the strain gauge.

Each socket has a strain gauge on each side (you can see the opposite side gauge on the far cable)

The black bands around the near cable hold the temperature sensor under the cable.

there is only 1 temperature sensor for a set of platform or backstay cables

Acquiring the data:

Data is sent via wire to a campbell scientific data logger

There is a datalogger at the top of each tower, and at T12 anchor and T4 anchor

The logger then sends the data via wireless modem to a base station (in phil's office)

The antenna on top of tower 4 acts as a relay for the station at anchor 4.

The downloadable data is sampled at 1 minute intervals

I need to find out the actual sampling rate and averaging that is done.

Manuals for the acquisition equipment:

cr6 data logger

rf451 radio

instruction manual (.pdf)

FreeWave spread spectrum wireless transceiver (oem board inside the rf451.. not sure of the model)

The data is uploaded from the base station in phil's office to the wje AO web page in chicago.

You can access the data via their AO website.

You can generate plots of the data
You can also download the data in csv format for a user requested date range.

The lvdt is not yet available for download (27oct20).

The temperature data

Plot the aux cable temperature data vs date, hour (.ps) (.pdf)

Colors label the cables
Note that all temperatures are taken on the tower (platform and backstay sides).
Page 1: cable temperature vs daynumber of year

Top: platform aux cable temps vs dayno
Middle: backstays aux cable temps vs dayno

Bottom: Tower PlatformTemp - Backstay temp

for 12 and 8 the main and backstay temp is on the same side: P12West -B12West,P8South-B8south
for 4 : P4South - B4North (P4north failed)

Tower 8 platform and backstay cable temps are noisier than t12, and t4.

Page 2: Cable temperature vs hour of day.

Top: Platform aux cable temps vs hour of day

Tower 12 has a few days with a large oscillation

middle: backstay aux cable temps vs hour of day.
bottom: Platform - backstay cable temps.

Page 3: average cable temperatures

The data from each day is averaged.
During the morning:

T12 and T8 main cables heat up before the backstays
T4 backstay heats up before the main cables
This is just the geometry of the cable and sun.

You would expect that a temperature difference in the main,backstay would be seen it the tower tilts (see below).

processing: x101/cables/wjepro/plottemp.pro

Tower 8 and tower12 temperature oscillations (.ps) (.pdf)

Page 1: 12oct20,25oct20 platform and backstay cable temps

The green T8 temps are noisier on 12oct20 and continue noisy through the current date
the Black T12 temps show an oscillation on 25oct20. the started around 20oct20.

Page 2: blowup showing T8 temp oscillation

this is the first 100 minutes of 12oct20. The data is sampled at 1 minute intervals
The oscillation amplitude is +/- .5 deg F. The period is 8 minutes.
The oscillation is in the platform and the backstay data. It is probably a sampling or processing error.

Page 3: fft of the temperature data showing oscillation frequencies

This uses 15 days of data.
The green data peaks around 2.08 milliHz or 8 minutes. It is present in the platform and backstay temps of T8
You can also see a peak around .6- to .7 milliHz (24 to 28 minute period) in the T12 data (platform and backstay).

Page 4: Tower 12 temperature oscillation

data for 8am to 12pm is over plotted for 20-25oct20
Top: T12 platform temps showing the oscillation during the day
Bottom: T4 platform temps for the same time period. No oscillation.

Page 5: blowup of T12 oscillation

A linear fit was subtracted from the 8-12 data.
top: T12

on 23oct20 there were 10 periods in 4 hours (24 minute period).
the amplitude is up to +/- 2degF

Bottom: T4 temps show no oscillation.

processing: x101/cables/wjepro/tempdiag.pro

Histogram of cable temps shows dropouts every .5 degF above 80F(.ps) (.pdf)

The binsize of set to .1 deg F.
Page 1: 70 to 95 degrees.

There are no counts in a fixed spacing above 80 F.
This is not seen below 73 F

Page 2: Blowup 80 to 85 degrees

The 0 count bins are every .5 degF
This occurs for all temperature measurements

I don't know the resolution of the temperature sensors
If the data is being averaged over say 60 seconds, then you would expect the resolution to increase.
It's odd that this resolution limit is not seen on the low side of the temperature range..

processing: x101/cables/wjepro/temphist.pro

Rate of change of temp vs hour of day (.ps) (.pdf)

the temperature data was interpolated to 1 minute samples (in case there was missing samples)
The temperature rate was computed by subtracting adjacent samples.
Page 1: temp Rate vs hour of day 0-24 hours

Black is the platform aux cables temperature rate.
red is the backstay temperature rate
The 3 frames are T12,T4, T8
The digitization during the day may be coming from the dropouts seen in the histograms above.
The vertical spikes in T12 are the 24 minute oscillations
The large spread in the T8 rates come from the 8 minute oscillations.

Page 2: blowup temperature rates 8 to 11 am

Each day is over plotted in a separate color
Each frame is a separate tower
I've offset the Main +.5F/min and backstays -.5F/min for display.
Top: t12

The large oscillations are the days with the 24min oscillation
Looking closely at AuxMainW there is a coherent temperature rate oscillation 8am to about 9am

I think this is a shadowing of T12AMainW by the other T12 cables as the sun rises.
As it moves up , each main cable can shadow the T12aux for a short period of time.

Middle T4; looks normal
bottom:T8 : large from 8 minute oscillation.

processing:x101/cables/wjepro/temprate.pro

Temperature summary

Temperature difference Platform - backstay

T12

T12Pwest is always warmer than T12Bwest.

T4:

T4BNorth warms much faster than T4Psouth
around 9:30 am the trend reverses and the platform begins to catchup.

T8

There is less difference in the T8 platform and backstay cable temperatures.

T8 temperature values have an 8 minute oscillation of +/- .5degF.

This is probably from the data acquisition (the actual temperature is not doing this)

T12: shows 24 minute oscillations during the day. starting around 20oct20.
Histograms of the data with .1 deg bin size show no counts every .5 deg above 80deg

If the data is being averaged for 60 seconds, this should not occur.
If the data is a single sample each 60 seconds then you might expect this.

Tower tilts

Tilt sensors on top of the tower measure the radial (in cable direction) and transverse tilts.
I don't know how accurately the sensors were mounted. There may be a dc tilt from the mounting. It is probably best to look at the change in tilt.

Plotting the tower tilts vs date and hour of day (.ps) (.pdf)

Page 1: tilts vs daynumber

Each tower is plotted in a different color
Top: radial tilts (positive is toward the platform).

T12 tilt was drifting down until dayno 294 (20oct20) when it stabilized.
T4 has the largest change in tilt

Bottom: Tangential tilts vs daynumber

T12 is also showed in downward drift until 20oct20
T8 tangential tilt does not register.

Page 2: tilts vs hour of day

Top: radial tilts

T4 has the steepest decline in tilt
T8 has very little change in tilt.

bottom: tangential tilts

processing: x101/cables/wjepro/plottilt.pro

Plotting the radial tower tilts vs the (main-backstay) cable temperature differences (.ps) (.pdf)

Each tower if plotted in a separate color
The T12 data showed a drift in tilt.

To correct for this, a linear fit was removed from all tilts using data from 0-5am and 20-24 hours.

Data from 6:30 to 10:00 hours were used for the main- backstay temps.
There is a clear correlation between the tower radial tilt and the temperature difference of the main and backstay cables.
Tower 4 has the largest temperature difference as well as the largest tilt.

Tower 4 tilt of .03deg is .128' or 1.5 inches at the top of the tower if you use 245' for the height of T4.

The 1960 drawings say the standard motion can be up to +/- .1 ft.

It looks like the sign of the radial tower tilt might be reversed.

Temp tower - temp Backstay < 0 --> the backstay cables are hotter
If the backstay cables are warmer, they should stretch more and lower their tension
So the tower should tilt toward the main cables (or platform).
The current definition of the tilts says a tilt toward the platform if positive.
We are seeing a negative tilt in the tilt data.

processing: x101/cables/wjepro/tiltvstempdif.pro

Strain gauge differences

Each aux socket at the platform has a strain gauge on each side of the socket. The plots below plot the difference in strain
vs various parameters.
Notes:

When processing the data i've removed the original strain gauge sample from each measurement set (so they all start at 0).
Plotting vs day, the x axis is labeled: yymmdd:hh
The "all" plots clip the T4 platform diff's so you can't see after the T4M break differences.. The "afterM4break" plots, center the vertical scale on the larger difference.

type of plot	Date range	Platform	Backstays
Vs date	All	(.pdf)	(.pdf)
Vs date	afterM4 break	(.pdf)	(.pdf)
Vs hour of day	All	(.pdf)	(.pdf)
Vs hour of day	afterM4 break	(.pdf)	(.pdf)
Vs cable temperature	All	(.pdf)	(.pdf)
	afterM4 break	(.pdf)	(.pdf)

Summary of things to look into.

Things to be looked into:

T8 temps have an 8 minute +/- .5deg F oscillation
T12 temps have a 24 minute +/- 2degF oscillation that started around 20oct20
With a histogram of .1 degF binsize, there are bins with no counts every .5 deg starting at 80F

If the data is being averaged, this shouldn't occur.

Tower12 tilts were drifting until 20oct20
Tower8 tangential tilts are all 0
It looks like the sign of the radial tilts might be reversed.