Title: optimising photomultiplier performance at low power
1optimising photomultiplier performance at low
power
- Tony Wright, Electron Tubes Ltd
VLVnT2 Catania 8 - 11 November 2005
2optimising photomultiplier performance at low
power
- battery operated
- solar powered ( Auger, satellite)
- under-water and under-ice experiments
heat generation is never a good thing!
- two considerations
- consuming the power (voltage divider)
- providing the power (power supply)
3voltage divider considerations
- Requirement
- establish maintain a set of fixed dynode
potentials - Two types available
- resistor type
- active divider (FET)
- The all-resistor divider always fails the
requirement but why and how - badly?
4all-resistor divider
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6two possibilities
- light source is absolutely constant
- mean anode current Ia does not change
problem goes away
- light source varies with time constant greater
than that of the voltage divider
gain will shift as Ia changes
7solutions
- increase ID0 by decreasing all R values
- or
- reduce R(dn-a) only
- use either a fully or partially active divider
based on emitter follower action - capacitors for pulsed signals
8active divider networks
9power supplies
- CW type with n individual socket outputs
- Active divider with n individual outputs
- Low power dc-dc converter with single output
- Industrial dc-dc converter with single output
10power supply outlines
PS1800/PS1806
PS2010
PS2001
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13power supplies
14Multichannel high voltage and control system for
photomultipliersHVSys
illustrating the system configuration for the
control and supply of up to 254 pmts. Only a
single 12V supply is required with the HV
generated by the individual power bases
15functional diagram of 1 channel. The hardware
shown is integrated within each power base
enclosure
16illustrating the superior performance of an
active divider compared with conventional
resistor types. One of the basic requirements of
any detector is that its gain should remain
constant and independent of input signal
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18current per channel as a function of mean anode
current with 12 V supply. The inset illustrates
the low power consumption for multiple channels
19specification
(1) at 1 kV, per power base (2) 100 k? //5 pF
load (3) to within 1 (4) to 40 V output
20summary and features eliminates expensive and
bulky HV cable and connectors one PCI card can
control up to 254 individual power bases
system expansion is possible via additional
RS485 cards programmable options for setting
and monitoring parameters utilises up to 16
preset voltage settings low power consumption
per power base exceptional dc and pulse
linearity facility for monitoring temperature
or other transducers high voltages are
restricted to the power supply and
photomultiplier this reduces the electrical
shock hazard associated with traditional
multi- channel power supplies graphical
display of parameters easy maintenance
21Simplistic explanation g a Vn
dg n dV .(1)
g V but dV ? Ia R where Ia is the
mean anode current, n ? 10 and V 1000 volts low
power consumption dividers typically use 1 M?
resistors and draw 100 ?A divider current, so
dg 10 (10-6 x 106) g
1000 1 per ?A of Ia