FAST ComTec MCA4A, User Manual

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Software Description
4.1.7 ADC Settings
Clicking the ADC Settings button in the Settings overview the ADC Settings dialog as shown in Fig. 4.10.
Here all parameters like range, etc. for PHA mode and SVA mode can be set. Select the ADC in the drop-
down listbox at top right. The Enable checkbox must be checked if the corresponding channel is active. The
ADC resolution and length of the spectrum is set by the Range listbox between 2 and 65536 in binary steps.
For the Gate input there is a choice between Don't Use, COINC, ANTI and REJ IN.
COINC means that the voltage level at the Gate input must be high to trigger an event, ANTI means that the
level must be low. A pull-up resistor in COINC mode and a pull-down resistor in ANTI mode lets the input
work if no gate input is connected, see . The gating is evaluated at the time of the threshold crossing. Set All
sets the range and Gate mode for all ADC's.
The SCA 3 boundaries can be set with the SCA Lower, Upper edit fields. Here the units are in LSB's of the 16-
bit ADC, i.e. full range is from 0 to 65535. If an event is recorded inside the SCA boundaries, a pulse signal
can be output at the corresponding monitor output at the feature connector.
The Threshold for triggering an event can be set in mV, an event will be triggered if the voltage level crosses
the zero plus threshold level. The Get Zero button calibrates the offset voltage level. It is recommended to
connect no signal when doing this offset calibration. The offsets will be saved into the default settings file
MCA4A.SET by clicking “Save” in the hardware settings dialog, and automatically reloaded when the
software is started next time. See chapter 2.5.1. As the offset calibration can cause a shift in the spectrum,
be careful not to do a new “Get Zero” within a series of measurements. The pulse height spectrum shown in
the MPANT program is an histogram of the ADC data, the offset is subtracted. Therefore the maximum pulse
height value that can be recorded when using a 64k range is 64k minus the zero value. The maximum
3 SCA: Single-channel-analyzer
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Fig. 4.10: ADC Settings dialog, right: Scope mode