MPD-4(Data sheet V2.12_01)

4 channel particle
discriminator module
for liquid scintillators

mesytec MPD-4 is a four channel pulse shape discriminator module. MPD-4 is used forparticle discrimination in multi channel liquid scintillation detectors (for example BC501 orNE213). The identification signals are available as NIM and ECL pulses.
For discriminator monitoring only 2 channels of peak sensing ADCs per scintillator channel
are needed. Fast preamps are integrated. The 4 channel unit fits into a single width(1/12) NIM module.
Features:• fast variable gain PMT input amplifier• Signal filter, optimised for liquid scintillators• Pulse shape detection unit based on a constant fraction
discriminator (CFD) for rising edge start and a zerocrossing detector for tail length detection. The measured
tail length is converted to an amplitude signal via time toanalog converter (TAC)• for monitoring:• TAC output pulse (1 us) for neutron identification,
amplitude independent• Amplitude output pulse (1 us)• Identification signals:• Gate output (n +  signals)• Trigger output selectable n or  or both• Common trigger output, NIM, chainable(also usable as ADC gate).
• Multiple ECL trigger and amplitude / TAC signals at therear side.
• in fast mode:• deadtime reduced to 250 ns. Trigger output width
reduced to 30 ns. Analog outputs suppressed.
• all parameters can be set via front panel, USB or
mesytec control bus.

mesytec GmbH & Co. KG
Wernher-von-Braun-Str. 1, D-85640 Putzbrunn, Germany
phone: +49 - 89 / 456007-30 fax: +49 - 89 / 456007-39
info@mesytec.com - www.mesytec.com

MPD-44 channel particle discriminator

MPD-4 Schematics:

mesytec GmbH & Co. KG
Wernher-von-Braun-Str. 1, D-85640 Putzbrunn, Germany
phone: +49 - 89 / 456007-30 fax: +49 - 89 / 456007-39
info@mesytec.com - www.mesytec.com

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MPD-44 channel particle discriminator

4-fold channel section
Input:

PMT signal input (anode signal, negative), terminated with 50 Ω.
Variable gain by a factor of 20 in 16 steps.
Gain = 0 means a maximum signal of –3 V, gain = 20 means max –150 mV.
Ampl_out:

Integrated PMT charge output. Full range of 4 V and 8 V can be selected via
internal jumper.
TAC_out:

Corresponds to ratio of fast to slow component of scintillator light output. Fullrange of 4 V and 8 V can be selected via internal jumper.
Gate_out:

NIM pulse when signal exceeds CFD-threshold, not particle selective. Length isadapted to deliver ADC gate for Ampl and TAC outputs.
n/g-Trig:can be configured as neutron, gamma, all or reject output.
NIM-signal, adapted to deliver ADC gate for Ampl and TAC outputs.
accept LED:

lights up when signal exceeds CFD-threshold, is below maximum value, has aprocessable amplitude ratio of fast and slow component.
reject LED:

lights up when signal exceeds CFD-threshold and is not accepted.
Also works as channel indicator during channel adjustment.

Control section:“Chan” switch:

toggles around the following channel selections:
C1 → C2 → C3 → C4 → no channel selected (but in single channel mode)→ common (all channels selected). The selected channel will light its “reject”
LED as indicator.
“Para”-switch:

toggles around the following parameters to be tuned: thresholds → n.dis → gain.
Input_coder:central input device for all parameters: the selected parameter in the selectedchannel(s) is modified.
“fast” switch:

switches between fast an slow moderate
Sense / gnd output:

The currently tundes parameter is represented as a voltage from 0 to +2 V
Common trigger output:

NIM-trigger when any of the 4 trigger outputs respond. NIM current output–16 mA, can be dasy chained with other modules. In fast mode it outputs “all”.
TAC-outputs:

for position sensitive detectors, provides position signal.
Settings will be saved in parmanent memory and will be restored afterpower up.
mesytec GmbH & Co. KG
Wernher-von-Braun-Str. 1, D-85640 Putzbrunn, Germany
phone: +49 - 89 / 456007-30 fax: +49 - 89 / 456007-39
info@mesytec.com - www.mesytec.com

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MPD-44 channel particle discriminator

RC bus section
Bus:

Lemo input for the mesytec rc bus. Has to be terminated with 50 Ω at the lastdevice in chain.
ID:Bus address (0 … 9 … F), each device on a bus has to have a unique address.

Output section
TAC_/ Amplitude out:corresponds to ratio of fast to slow component of scintillator light output.
Full range of 4 V and 8 V can be selected via RC.
Trigger – ECL:

ECL pulses. Length adapted to deliver ADC gate for Ampl and TAC outputs.
Three different triggers are available per channel.

Serial connection
USB:

Serial connection for device control.
Virtual Com Port drivers for several operating systems can be found atwww.ftdichip.com/Drivers/VCP.htm

mesytec GmbH & Co. KG
Wernher-von-Braun-Str. 1, D-85640 Putzbrunn, Germany
phone: +49 - 89 / 456007-30 fax: +49 - 89 / 456007-39
info@mesytec.com - www.mesytec.com

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MPD-44 channel particle discriminator

Jumper settings
Inside the MPD-4 there are four jumper positions
to control the output voltage and the source forfront trigger, ECL trigger and “common” outputs.

A label inside the device also shows these settings

Parameter setting

Qwin

Threshold

The PMTs are directly connected to the inputs.
The CFD threshold is preadjusted to an offset of
1 % full range, allowing a dynamic range of
100:1. For lowest threshold setting we suggest topower on the detectors, remove any source andadjust the threshold to give a low or no count rate.
gain

The "gain" value should be selected as low aspossible. Prefer to increase the PMT voltage
which will result in better noise immunity of theconnection from PMT to MPD-4.
ndis

The MPD-4 TAC-output has a fixed discrimination threshold of 1.9 V (0.95 V in 4 V mode) todiscriminate neutrons from gammas. If the TAC
output is below the threshold, gammas are identified, above the threshold neutrons are identified.
With '"ndis" parameter the TAC outputs can beshifted up and down to get the correct identification cut.
The typical difference in TAC amplitude for neutrons and gammas are 1 V to 1.5 V (8 V range).
walk (adjustment range 50...150)

If the maximum discrimination resolution isneeded, the additional parameter "walk" can be
adjusted: take a spectrum "Ampl vs. TAC" withgammas on the scintillator and adjust the curvewith the "walk" parameter to get a flat top for thegamma line. The "walk" parameter influences theTAC amplitude in the low energetic region.

is only for outmost optimisation purpose andshould normally not be changed (default = 100).
It will also influence the "walk" parameter.
Stability of TAC signals

The MPD-4 has to handle output signals of manydifferent PMTs combined with different scintillator liquids and scintillator geometries. So thefactory calibration only can give start values for“walk” and “ndis” values. Some detector combinations may give no defined output values with thedefault settings. In this case start with a significantly higher value of “walk” and then adjust it
down to the correct value. Also “ndis” may not bea good start value and has to be adjusted.

Operating modes
Slow mode

Used for system adjustment or very precise measurements or at moderate rates to preserve all information. Amplitude and TAC signals are available. Dead time is determined by the Amplitude
and TAC output signals and the conversion andreadout time of the external peak sensing ADC(typ 2 us with MADC-32).
Fast mode

For non position sensitive scintillator panels,
usually only the number of neutron hits within theacquisition time is important. By using scalers tocount neutron events and, if necessary, total
number of events (for dead time determination)
the amount of data and the dead time can be
reduced by large factors. The MPD-4 allows toswitch to fast mode which reduces the total deadtime to 250 ns.

mesytec GmbH & Co. KG
Wernher-von-Braun-Str. 1, D-85640 Putzbrunn, Germany
phone: +49 - 89 / 456007-30 fax: +49 - 89 / 456007-39
info@mesytec.com - www.mesytec.com

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MPD-44 channel particle discriminatorstandard mode fast mode

Command list

Ampl_out

1 us long pulse,
4V/8V-(each cmd terminated by <CR>)

TAC_out

1 us long pulse,
4V/8V

-

VER
DS

trig-Gate_out

1 us long pulse

60 ns

Gam/n_out

1 us long pulse

60 ns

Pos_TAC

1 us long pulse-rear side ECL

1 us

60 ns

com trigger

1 us

60 ns

common position
TACs

1 us long pulse
4V/8V

-

dead time per event

1.25 us250 nssignal

SN chan val
ST chan val
SW chan val

Power consumption+12 V+6 V–6 V

SG chan val

120 mA
600 mA–800 mA

CCCS

Remote Controlled Operation

MPD-4 can be remotely controlled in two modes:
USB control and mesytec remote control (MRC).

SQ chan val

USB Control

For USB control a USB 1.1 or 2.0 connection isrequired. The MPD-4 operates as a generic serial
device on a virtual com port. Virtual Com Port(VCP) drivers for various operating systems forthis rc mode can be derived from the manufacturerof the USB interface chip:www.ftdichip.com/Drivers/VCP.htm
The MPD-4 can then be controlled e.g. using aterminal program or a proprietary control software.

show firmware revision
Display Setup(lists gains, thresholds,Ndis values, mode,…)set Gainchan = 0…4 (4 = all common)
val = 0…15
set Ndis valuechan = 0…4 (4 = all common)
val = 0…255
set Threshold valuechan = 0…4 (4 = all common)
val = 0…255
set corr. value for Walk
chan = 0…3
val = 100 ± 50 (100 = no corr.)
set to common mode
only FW-Rev ver 2.7 and higher
set to single mode
only FW-Rev ver 2.7 and higher
Set corr. value for integration
window for short signal
componentchan = 0…3
val = 100 ± 100 (100 = no corr.)
Default values need not to bemodified normally.

Settings via USB remote control will also be
saved in permanent memory and will be restored
after next power up. For Fw-Rev 2.7 and higher
common or single mode should be set to define
which parameter set to load (also at next powerup). In the older revisions this selection must be
done via front panel switch. Set to “none” toselect single, and “common” to set common mode
set. The push button must be pressed at least once
after USB programming.
MRC control

MPD-4 can also be controlled using the MRC-1
controller module.
Up to 16 modules (not only MPD-4) can beconnected on one bus, up to 32 on the two busesof the MRC-1, just using T-pieces.
The last module on a bus has to be terminatedwith 50 Ω.
Remote control via MRC-1 is basically reading
and writing the control register page ofthe MPD-4.
mesytec GmbH & Co. KG
Wernher-von-Braun-Str. 1, D-85640 Putzbrunn, Germany
phone: +49 - 89 / 456007-30 fax: +49 - 89 / 456007-39
info@mesytec.com - www.mesytec.com

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MPD-44 channel particle discriminator

Memory List MPD-4
MPD-4 can be controlled by reading / writing thecontrol register page via the mesytec rc bus.
The following table shows the memory layout:ADR parameter0
Gain channel 1
1
Gain channel 22
Gain channel 3
3Gain channel 4
4
Ndis channel 1
5
Ndis channel 2
6
Ndis channel 3
7
Ndis channel 4
8Qwin channel 1
9Qwin channel 210Qwin channel 3
11Qwin channel 412131415
16
171819232540

comment
Gain setting forchannel 1 … 3,Values from 0 … 15
TAC shift forchannel 1 … 3,
Values from 0 … 255

Corr. val. f. integration of short sign.
Component, Values
100 ± 100
(100 = no corr.)
Threshold channel 1 Threshold settings
Threshold channel 2 for channel 1 … 3,Threshold channel 3 Values from 0 … 255
Threshold channel 4
Walk corr. channel 1 Offset to factory
Walk corr. channel 2 walk correction
Walk corr. channel 3 Values 100 ± 50
Walk corr. channel 4 (100 = no offset)
Fast mode
0 = slow mode
1 = fast mode
Output range
0=4V(read only)
1=8V
Output source
Output source for(read / write)
trig
falls back to jumper outputs:
setting after power 0 = neutrons, 1 =up and "RC off"
gammas,2 = reject, 3 = all(n+g)

The memory positions can be written with
SE command and can be read with RE command.

RC mode has to be ON for writing,reading is possible also with RC OFF.
While RC ON, front panel control will beblocked.
The ON/OFF command makes the remote control
active or inactive. The power up default is inactive. While inactive the manual values from thefront panel elements are set.
When shut down during RC on, the RC values
will be restored after next power up and rc will be
active again. Output range and source will restartwith jumper setting.
Command Summary

Each MRC command has to follow the format
described below.
CMD bus [dev] [adr] [val]data formats:busdevadrval= bus number [0...1]= device number [0...15]= parameter number [0...31]= [0...255] (or [0...15] for gain);Mnemonic Description
SC busreturns id code:
IDC = 21

ON bus dev

activate rc fordevice dev on bus bus

OFF bus dev

turn off rc fordevice dev on bus bus

SE bus dev adr val

set memory cell adr for
device dev on bus bus
to value val

RE bus dev adr

read memory cell adr
from device dev onbus bus

mesytec GmbH & Co. KG
Wernher-von-Braun-Str. 1, D-85640 Putzbrunn, Germany
phone: +49 - 89 / 456007-30 fax: +49 - 89 / 456007-39
info@mesytec.com - www.mesytec.com

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