Among other thngs, during the week of the 11th of January, we measured the altitude (z direction in the VRS system)  of the 3 detection benches in the detection lab, i.e. SDB1, SDB2, EDB.

 

To measure this we use a leica level set on a tripod, and took as a reference the altitude patches glued on the wall of the detection lab.

 

SDB1 measurement :

 

To measure the SDB1altitude, we set the leica level on the north side of the detection tower and we looked at the SDB1 bench through a viewport.

This viewport has no tilt in the vertical direction, and a very small wedge (of about 100 urad), so its impact is negligible.

It should be noted that one should look through the viewport far from its edges as it degrades the visibility through the leica level  and so perturbing the measurement.

 

We placed a height ruler at different position on SDB1, and read with the leica level the value on the ruler (h), the measure are reported below for different position on SDB1(x,y) of the ruler :

x = 75 mm, y = 0 mm ==> h = 249.9 mm;

x = 100 mm, y = 0 mm ==>h = 249.9 mm;

x = 150 mm, y = 0 mm ==> h = 249.9 mm;

x = 250 mm, y = 0 mm ==> h = 249.9 mm;

x = 150 mm, y = -50 mm ==> h = 249.9 mm;

x = 150 mm, y = 75 mm ==> h = 249.9 mm;

 

This height correspond to an altitude of 156 mm in the VRS.

 

It gives us the altitude of the bench SDB1, z = 156 - 249.9 mm = -93.9 mm

 

According to the document "The reference solution to deal with vertical wedge" (VIR-0267C-15), the bench should be at an altitude of -92.9 mm

Then we found SDB1 to be 1 mm too low.

 

This measurement also gives us an estimate of the pitch (Tx) and roll (Ty) angles of this bench.

Considering that the value read on the ruler was always the same we can estimate this read-out error to be of +-0.1 mm.

 

So the pitch and roll angles of SDB1 are of 0 mrad +- 0.8 mrad and of  0 mrad +- 0.57 mrad respectively.

 

SDB2 measurement :

 

Using the same method for SDB2, we set the leica level on the north side of SDB2 on its tripod and look at the height ruler set on the SDB2 table.

At each corner, we read the value on the ruler :

SE : h = 245 mm

SW : h = 244.9 mm

NE : h = 247 mm

NW : h = 246.5 mm

 

This height correspond to an altitude of 153 mm VRS.

 

Then the altitude of SDB2 is on the north side : z = 153 - 246.75 mm = -93.75 mm

Then the altitude of SDB2 is on the south side : z = 153 - 244.95 mm = -91.95 mm

 

SDB2 roll angle (Tx) is then of (246.75 -244.95)/1250 = 1.4 mrad +- 0.1 mrad.