GBS Elektronik MCA 166 - Manual (Page 24)

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The MCA-166 must be connected to the detector of your choice (usually HPGe or other high-resolution
detector) and to the computer (see chapter 2). Place the detector in correct position for a measurement.
Switch on the MCA-166 and the computer, and start the SPEC User Program. Usually you will have a setup
file prepared and stored on your computer, which is specific for your task and the detector to be used. By
reading this file, the correct settings of the MMCA will automatically be restored. You will need only switch on
the HV and a fine tuning of the gain (in case of high-resolution measurements also of the pole-zero
adjustment) before starting a measurement.
Once SPEC is started, you should reset the MMCA (answer the corresponding question in the startup screen
with Yes). Navigate through the menus with the Arrow and Tab keys, open a menu with the Enter key, accept
settings by leaving a menu with the Escape and Enter keys. Use the context-sensitive on-line help which is
available if you press the function key F1. In the menu screens which are used to define or change settings,
the active fields are highlighted. You will find information on how to change the highlighted parameter in the
bottom line of the active menu screen. The user interface of the SPEC program is almost identical with the
generic multi channel analyzer program MCA, which is described in chapter 3.2
To start a measurement, proceed as follows:
• Read the setup file prepared previously: Setup => Read setup file.
• Switch on the HV: Setup => Detector high voltage setup.
• Choose your preset (life time, real time, or none): Setup => Presets.
• Check - or change, if necessary - the MCA resolution (channels), thresholds, lower/upper levels for
spectrum collection: Setup => MCA Setup
.
The optimum choice for your task is probably already defined in the setup you read in, but you have access
to all of these parameters. Here you can also toggle the options for the signal input (internal amplifier,
direct input of positive or negative signals from external amplifier).
• Adjust the fine gain:
Setup => Amplifier setup => Do visual gain adjustment
.
• Check the PZC adjustment:
Setup => Amplifier setup => Do visual PZC adjustment.
The displayed value of Zero offset should be 0±2. Correct if necessary.
Check again the fine gain adjustment if large changes were necessary in the PZC adjustment.
Now you are ready to measure a spectrum. With Data acquisition => Measurement you
enter the graphics screen (Acquire screen). Possible operations like Start / Stop / Expand / Change vertical
full scale (Y) and others are indicated at the bottom text line (which is adapted to the HP 200LX Palmtop
computer) and controlled by the function keys F2 - F10. Use F1 to obtain more detailed information about
possible operations in the Acquire Screen!
Other operations like saving spectra and getting information about peak areas, centroids, and integrals in
regions of interest (ROIs) are possible only if you enter the Evaluation screen (press F2!). Once a
measurement is finished - either by pressing F5 or by reaching the chosen preset - the Evaluation screen is
automatically activated. Now you may save a spectrum by pressing F4. To start the next measurement, you
must switch back to the Acquire Screen (F2). Exiting the graphic screen is always possible (press F10), even
if a measurement is still running. You may come back later to the Acquire Screen (choose Data
acquisition => Measurement
) and inspect your running (or finished) measurement.
Here you find a brief list of features which are available in SPEC:
• Defining ROIs: Move the cursor to the ROI begin, press the Shift key, move the cursor to the ROI end
while pressing Shift, release the Shift key. The selected ROI is highlighted.
• Deleting ROIs: Move the cursor into the ROI, press the Del key.