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CHAPTER 2
BEAM LOSS MONITOR PROCESSOR MODULE (BLMP)
BLMP description
The BLMP (Beam Loss Monitor Processor module) is a CAMAC module
designed to monitor radiation levels in the PEP-II ring
tunnels. It accepts signals from the BLM sensors (Cerenkov
light detectors followed by miniature photomultiplier tubes),
provides diagnostic outputs via CAMAC, and feeds the Beam Abort
Logic system.
General
Module width: single
Channel count: 10
Input connector: Lemo 00.250
Connector to HV box: 4 pin Lemo 1B.304
Connectors to abort system: 6 pin Lemo 1B.306
Pulse counter: 24 bits, update time selectable 10 ms or 1s
Integrated signal: 10 us integration time, 12 bit ADC,
updated every 9.2 ms or on inhibit signal end
HV power: 1000v, 10 mA
Pulse Counter
The individual pulses from the detector are amplified,
discriminated, and sent a 24 bit counter. The threshold for
the discriminator is adjustable by one 12 bit DAC for the whole
module. Average maximum counting frequency is limited, by the
24 bits, to 16.7 MHz. Peak counting frequency is limited, by
the counter architecture, to 40 MHz (25 ns between pulses).
Depending on the phase relations between the input pulses and
the internal clock, pulses can be missed up to 37.5 ns between
pulses. Above that, all pulses will be counted. Every 1
second or 10 ms, the data from all counters is latched and the
counters zeroed.
Integrated signal readout
After the signals are picked off for the counter, they are
integrated on a capacitor with a 10 us integration time. this
signal is amplified and sent to a 12 bit ADC. The total
BEAM LOSS MONITOR PROCESSOR MODULE (BLMP) Page 2-2
conversion (10 input channels plus 1 HV readback channel) takes
about 211.2 us (19.2 us per channel). This is performed every
9.2 ms or on the fall of the abort inhibit signal, whichever is
sooner. This feature allows the ADC conversion to be
synchronized with the injection to look for losses at that
time.
Beam Abort system
The integrated and amplified signal is compared to a threshold.
Each channel has a separate 12 bit DAC for the threshold
setting. If it is higher and that channel is enabled for HER,
the HER abort signal is sent. If it is enabled for LER, the
LER abort signal is sent. The data and the abort signals are
latched until cleared by CAMAC. The abort system can be
inhibited by a front panel signal. This is to prevent unwanted
aborts at injection time. When the module is in an abort
state, (internally generated or received from another module)
all normal data updates are suspended. The data does not change
until the abort has been cleared by CAMAC. This feature
(freeze mode) can be disabled by a CAMAC command.
HV system
The high voltage for the BLM detectors is supplied from a
separate module powered and controlled by the CAMAC module.
The CAMAC module will send 24v power and a control voltage from
a 12 bit DAC. The box will return a voltage proportional to
the actual high voltage out. This will be sent to a 12 bit ADC
for CAMAC readout.
Security Feature
All CAMAC commands that control systems that are part of the
MPS (Machine Protection System) require that a special command
be sent first to unlock the module. These are the abort
threshold settings, the high voltage control DAC, and the beam
abort masks. The module must be relocked by another command.
Diagnostic Features
The abort signals form a continuous loop from module to module.
An abort anywhere will force the whole loop low (abort). signal
interruptions (damaged cable, unplugged connectors, faulty modules
etc.) could be difficult to locate. To help with this, there is a
special diagnostic mode which forces the abort output high, regardless
of the state of the input. The signal can then be traced, and the
interruption located. This should only be used when there is no
beam. Similarly, it would be difficult to tell if the inhibit
signal is being received properly by the modules. There is a
special test command that reads OK for 50 milliseconds after
an inhibit has been received. In practice, this would read
continuosly OK during injection (inhibits sent 40-120 Hz), and
BEAM LOSS MONITOR PROCESSOR MODULE (BLMP) Page 2-3
not at other times.
Command List for BLMP
F0 A0 read back threshold setting for for beam abort, ch 0 (12 bits)
F0 A1 read back threshold setting for for beam abort, ch 1 (12 bits)
.
.
.
F0 A9 read back threshold setting for for beam abort, ch 9 (12 bits)
F0 A10 read back threshold setting for counter discriminator (12 bits)
F0 A11 read back DAC setting for HV (12 bits)
F1 A0 read ADC for ch 0 (12 bits)
F1 A1 read ADC for ch 1 (12 bits)
.
.
.
F1 A9 read ADC for ch 9 (12 bits)
F1 A10 read ADC for actual high voltage output
F2 A0 read counter for ch 0 (24 bits)
F2 A1 read counter for ch 1 (24 bits)
.
.
.
F2 A9 read counter for ch 9 (24 bits)
F3 A0 read module serial no. (16 bits)
F3 A1 read module ID no. (16 bits)
F3 A2 read module revision no. (16 bits)
F4 A0 read back abort mask HER loop (11 bits)
F4 A1 read back abort mask LER loop (11 bits) see table 1
F5 A0 read trip state latch (10 bits) see table 1
BEAM LOSS MONITOR PROCESSOR MODULE (BLMP) Page 2-4
F6 A1 counter update readback--data = 1 update every 10 ms data = 0
update every 1 s
F6 A2 freeze mode readback--data = 1 updates are not frozen on abort.
data = 0 updates are frozen on abort.
F6 A3 bypass state readback--data = 1 abort signals bypassed on
power-off. (power-off will not cause an abort). data = 0 abort
signals stopped on power-off. (power-off will cause an abort).
set by hardware jumpers.
F6 A4 test abort loop input--HER loop; data = 1 means input is high
(not abort)
F6 A5 test abort loop input--LER loop; data = 1 means input is high
(not abort)
F6 A6 test activity on inhibit input--data = 1 means a pulse has been
received on the abort inhibit line within the last 50 ms.
F8 A0 clear trip state latch (no data)
F16 A0 set threshold for beam abort for ch 0 (12 bits) (module must be
unlocked Q=0 if not permitted)
F16 A1 set threshold for beam abort for ch 1 (12 bits) (module must be
unlocked Q=0 if not permitted)
.
.
.
F16 A9 set threshold for beam abort for ch 9 (12 bits) (module must be
unlocked Q=0 if not permitted)
F16 A10 set threshold for counter discriminator (12 bits)
F16 A11 set DAC for HV (12 bits) (module must be unlocked Q=0 if not
permitted)
F19 A0 set module serial no. (16 bits) (jumper required) wait 10 ms
before any other F19 or F3 commands
F19 A1 set module ID no. (16 bits) (jumper required) wait 10 ms before
any other F19 or F3 commands
F19 A2 set module revision no. (16 bits) (jumper required) wait 10 ms
before any other F19 or F3 commands
F20 A0 set abort mask HER loop (11 bits 0-9 for ch0-9, 10 for
diagnostic) (module must be unlocked Q=0 if not permitted)
BEAM LOSS MONITOR PROCESSOR MODULE (BLMP) Page 2-5
F20 A1 set abort mask LER loop (11 bits 0-9 for ch0-9, 10 for
diagnostic) (module must be unlocked Q=0 if not permitted) Bit n
set to "0" means ch n above threshold will abort beam. "1"
means ch disabled (see table 1)
F22 A1 set 10 ms counter update--data = 1 update every 10 ms data = 0
update every 1 s
F22 A2 set non-freeze mode--data = 1 updates are not frozen on abort.
data = 0 updates are frozen on abort.
F22 A3 dummy command--returns X and Q (for bypass state readback)
F22 A4 data = 1 set abort loop diagnostic--HER loop. Abort loop output
is forced high (not abort); input is ignored. Cleared after 45
seconds. data = 0--clear abort loop diagnostic--both loops
(module must be unlocked Q=0 if not permitted)
F22 A5 data = 1 set abort loop diagnostic--LER loop. Abort loop output
is forced high (not abort); input is ignored. Cleared after 45
seconds. data = 0--clear abort loop diagnostic--both loops
(module must be unlocked Q=0 if not permitted)
F22 A6 dummy command--returns X and Q (for inhibit input test)
F24 A0 clear abort loop diagnostic--both loops
F24 A1 clear abort loop diagnostic--both loops
F26 A0 set abort loop diagnostic--HER loop. Abort loop output is forced
high (not abort); input is ignored. Clears after 45 sec.
(module must be unlocked Q=0 if not permitted)
F26 A1 set abort loop diagnostic--LER loop. Abort loop output is forced
high (not abort); input is ignored. Clears after 45 sec.
(module must be unlocked Q=0 if not permitted)
F27 A0 test abort loop input--HER loop; Q=1 means input is high (not
abort)
F27 A1 test abort loop input--LER loop; Q=1 means input is high (not
abort)
F27 A2 test abort inhibit signal--returns Q=1 for 50 ms after inhibit
signal received.
F29 A14 unlock module for MPS functions
F29 A15 lock module for MPS functions
BEAM LOSS MONITOR PROCESSOR MODULE (BLMP) Page 2-6
Beam Loss Monitor CAMAC Module
table 1
beam abort mask spec.
HER abort loop
loaded by F20 A0, read back by F4 A0
bit 1 = "0" ch 0 enabled--will abort beam when above threshold
bit 1 = "1" ch 0 disabled
bit 2 = "0" ch 1 enabled--will abort beam when above threshold
bit 2 = "1" ch 1 disabled
.
.
.
bit 10 = "0" ch 9 enabled--will abort beam when above threshold
bit 10 = "1" ch 9 disabled
bit 11 = "0" will always abort beam, regardless of the state of the inputs
bit 11 = "1" allows normal operation
(diagnostic)
LER abort loop
loaded by F20 A1, read back by F4 A1
bit 1 = "0" ch 0 enabled--will abort beam when above threshold
bit 1 = "1" ch 0 disabled
bit 2 = "0" ch 1 enabled--will abort beam when above threshold
bit 2 = "1" ch 1 disabled
.
.
.
bit 10 = "0" ch 9 enabled--will abort beam when above threshold
bit 10 = "1" ch 9 disabled
bit 11 = "0" will always abort beam, regardless of the state of the inputs
bit 11 = "1" allows normal operation
(diagnostic)
Trip state latch, read by F5 A0, cleared by F8 A0.
bit 1 = "1" ch 0 was above threshold
bit 2 = "1" ch 1 was above threshold
.
.
.
bit 10 = "1" ch 9 was above threshold
Data is latched and remains until cleared by F8 A0. Data is available
BEAM LOSS MONITOR PROCESSOR MODULE (BLMP) Page 2-7
whether or not the channel is enabled for HER or LER.