GBS Elektronik MCA 166 - Manual (Page 19)

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LLD, ULD
LLD allows to set the lower level discriminator of the ADC. All channels below the LLD
value remain empty. The ADC deadtime, however, is not reduced. The value for LLD
must be < ULD. Default is 0.
ULD allows to set the upper level discriminator (ULD) of the ADC. All channels above the
ULD value remain empty. The ADC deadtime is not reduced. The value for ULD must be
> LLD. Default is highest possible channel.
In MCS mode (main application for this), if LLD/ULD is set, LLD and ULD define the limits
within impulses are counted.
In MCA mode, it is more recommended to use Threshold than LLD to remove noise and
low energy components of the spectrum.
ADC input (MCA mode)
Use the spacebar to toggle between the 2 different direct inputs ("+ 3V dir.", "-3 V dir.") if
you want to use, for e.g., an external amplifier, or select "Amplifier" in order to use the
internal amplifier. Default is amplifier.
Input Type (MCS mode)
Use the spacebar to select between "extern TTL" (pulses), "Input Rate" (from the MMCA
count rate meter) or LLD/ULD (Only impulses between the LLD/ULD limit are counted).
Default is TTL. This provides the highest countrate capability up to 10
6 cps.
Repeat (MCA mode)
Allows automated data collection and saving of spectra. After the preset is reached, the
spectrum is automatically recorded into a pre-selected subdirectory and then the next
measurement is started. At first a file with a filename using the scheme XXX00000.spe (3
letters and 5 digits) must be saved. XXX is user selected to distinguish between
measurement series kept in the same subdirectory. File name and directory are set under
File Save. Up to 65535 files can be automatically recorded. Default is 0 (no repetitive
measurements).
Sweeps (MCS mode)
Allows automated repetitive MCS spectra collection like Repeat in MCA mode.
3.2.2.3 Clear
Allows to clear all ROIs and all data in either the active or all memory groups. Clear ROIs:
Use the spacebar to select the right choice. Note: Set data option to "no", if only ROIs
should be cleared! Clear Data: Use the spacebar to toggle between "all" and "active
group" depending on which data should be deleted.
3.2.2.4 Active group
Allows to set one of 3 memory groups into which a spectrum is collected. The first group
is selected by default. Use the spacebar to toggle between active group 1, 2 and 3.
There are still some bugs within this function.
3.2.2.5 Mode
You can set the acquisition mode here either to MCA or to MCS mode. MCA mode
measures pulse height spectra which corresponds almost always to measure energy
spectra. MCS measures time dependent count rates. All channels correspond to an
equidistant sequence of time windows, the number of counts in the time window is stored