# NuMI BPM Sign Convention and Signal Path

P. Prieto

4/28/04

This note describes the sign convention used in the NuMI BPM system and
the labeling signal channels between the BPM's in the tunnel and the
electronics in MI60S, MI60N, and MI65.

# System Convention:

The sign convention in NuMI BPM system matches the sign convention of
BPM's located in the Main Injector. Measured positions delivered from
the VME front-end system have a positive sign for beam positions
radially outside at horizontal locations and positions above center for
vertical locations. This fixes the polarity of signals as POSITIVE
values corresponding to beam UP or OUT and NEGATIVE values corresponding
to beam DOWN or IN.

This same convention extends into the beam line going toward the NuMI
target. Measured positions at horizontal locations will have a positive
sign for beam to the right of center (radially outside) when looking
down the NuMi tunnel facing the target. Vertical locations will have a
positive sign for beam positions above center. This means that POSITIVE
measurement values correspond to beam UP and to the RIGHT (as defined
facing the NuMI target with your back to the Main Injector) and NEGATIVE
values correspond to beam DOWN and to the LEFT.

**BPM:**

NuMI BPM's are two-electrode electrostatic-type pickups with a
diagonally split cylinder of 3.85 in. diameter and 8.0 in. in length.
The same design, rotated appropriately, is used for both horizontal and
vertical locations. There is a doghouse on the body of the pickup where
a ceramic feed-thru connects each of the pickup plates to an N
connector. Not all BPMs are installed in the beam line with the
dog-house in the same upstream/downstream, right/left, or top/bottom
orientation. Nevertheless, at ALL vertical installations the upper and
lower N connectors attach to the top and bottom electrodes respectively
and similarly, at ALL horizontal installations, the radial inside and
outside connectors attach to the inside and outside electrodes
respectively.

**Cable Connections to BPM:**

The BPM signal cable labeling convention is a three row label with the
first row indicating the cable source, the second row the cable
destination rack and the third row the signal name. At horizontal and
vertical locations, cables are labeled for example, hp106 BPMA and hp106
BPMB indicating the BPM name and the plate to which its attached.

Care must be taken when connecting the cables to the BPMs in the tunnel
that the polarity convention is maintained regardless of the BPM
Nconnector doghouse orientation. At vertical BPM locations, the doghouse
will face out either the right or left side of the BPM. In either case,
the BPMB labeled cable should be attached to the upper N connector and
the BPMA labeled cable to the lower N connector. At horizontal
locations, the doghouse will face either up or down. In either case, as
you look down the beam line facing the NuMI target, the BPMB labeled
cable should be attached to the right-hand N connector and the BPMA
labeled cable to the left-hand N connector.

The cables from 13 BPM's go to MI60N and 12 BPM's to MI65 building.

The connections for MI0South originate from MI BPM's 02, 604, 605 and
606. Signal splitters have been added to the existing RG-8 cables using
RG-58 cables going to rack XXX where an 8 slot VME\^\$X crate with a
single DDC card downconverts the MI signals.

**Building and Top Plate Cabling:**

For MI60N (rack #MI60203) and MI65 (rack #MI65105) there is a rack
assigned and a top-plate N-type feed-thru. Each of the BPM signal cables
from the tunnel terminates at the rack top plate. A drawing will be made
of the top plate assignments.

An N-to-SMA transition cable, type LMR-195 and 36 inches in length,
connects the signals from the top plate to the transition module.

**Transition and Calibration Module:**

The NuMi PBM transition module (dwg. 9820-ED-3701755) is a four-channel
board capable of handling pairs of signals from two BPM's. A VME-style
crate will hold up to 7 transition modules in addition to one
calibration board that distributes the 53 MHz and 2.5 MHz calibration
signals to each of the transition modules. Inputs to the transition
board are made through four, rear edge-mounted SMA connectors. Input SMA
in the rear of the transition module are not labeled but the top SMA
corresponds to channel A1, second channel B1, third channel A2 and
fourth SMA channel B4. Therefore cables with labels BPMA or BPMB will be
matched to either the A channel or B channels in the transition board.
Outputs from the transition board going to the DDC board are from front
panel SMA's ,top to bottom, labeled A1, B1, A2, B2.

**DDC:**

The Echotek GC814 digital receiver board has eight independent
digitizer-down-converter-FIFO channels with front panel inputs labeled
0-7. Transition module "B" outputs connect to odd-numbered Echotek input
channels and "A" outputs connect to even-numbered Echotek input
channels. This maps the BPM pickup "B" plate to the upper input and the
"A"plate to the lower input of an Echotek even-odd channel pair.

Signal cables between the transition module and the Echotek DDC board
will be labeled with the BPM name at both ends, such as VP118-A and
VP118-B. These cables will be type FMR-195, 36 inches long, with SMA's
at each end.

**Software:**

NuMi BPM software is based on Recycler software and is currently being
implemented.