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STJ Quick Start Guide v 2.01
April 1, 2021
Page 13
Fig 7: The Auxiliary tab with an STJ Analog auxiliary module connected to the currently selected MPX-32D module.
STJ RELAY
The most important setting on this panel is the STJ Relay Enable/Disable button. By default, STJ Analog
on-board relays are open (as shown above): The STJ detectors are terminated with 1M
Ω
resistors, and the
preamplifier inputs are terminated with 10k
Ω
resistors in parallel with 2nF capacitors, i.e. a ‘dummy’
detector circuit. When the relays are closed/enabled, the preamplifier inputs are connected only to the
HDDSUB-78 pins, i.e. to the STJ detectors, if present. We recommend first familiarizing yourself with the
system by using the on-board pulser to generate an input signal before working with actual STJ detectors
(see below). Note that if the STJ detectors are not connected the HDDSUB-78 connector(s), the STJ Relay
provides a convenient ‘low noise’ pulser setting: the pulser signal is much cleaner when the dummy
detector circuit has been removed via the relay.
•
The “kill” toggle switch on the analog chassis prevents the STJ relays from closing when in the
left-hand position. Make sure this switch is in the right-hand position.
•
Click the STJ Relay Enable/Disable button so that it changes from green to red. Note that the
LED on the analog chassis corresponding to the selected STJ Analog module will change from
solid green to solid red when the relays are closed.
PULSER
The Pulser Settings control a rudimentary built-in pulser circuit, which feeds a periodic signal to all
preamplifier channels on the Analog Module. The signal is generated by a DAC on the MPX-32D which
repeatedly cycles through 4K points of waveform data stored in RAM. It is quite useful for debugging and
for exercising the data acquisition system. After system initialization the Pulser Enable/Disable button
should be green (as shown above), indicating that the pulser is turned off.
•
Press the button to enable the pulser, keeping the default settings as shown, which generates
a periodic pulse with a 1
µ
s risetime and 5
µ
s decay time, at 1 kHz frequency.
•
The PULSEGAIN setting coarsely controls the pulse amplitude, which is proportional to
2^PULSEGAIN. Valid PULSEGAIN values ranges from 0 to 3.
•
The PULSERINVERT setting controls the polarity of the pulse waveform. It should be set to 0 or
1 such that pulses are positive in the ADC waveform, as viewed in the Scope panel.