BNC 970 Portable Multi-Channel Analyzer (MCA) - Manual (Page 25)

Model 970 Instruction Manual 22
If Ramp HV is not checked, the High Voltage will change as instantaneously as possible. This
is usually fine for most detectors. If needed, Ramp HV can be checked and the detector
supply voltage will always be changed at the rate displayed. This can range from 6 to 219
seconds per 100 volts.
The detector Input and Polarity can be selected from the dropdown menu. INPUT1 is the
series “C” connector where signal and detector supply voltage are carried on the same line.
INPUT2 is the pair of separate connectors for signal and detector supply voltage, BNC and
SHV respectively. If “Shaped Input, Positive Polarity” is selected, either of the inputs can be
used. Note: If a shaped input is used, Coarse and Fine Gain controls will have no effect on
the spectrum input. Also, take care to ensure that shaped pulses are kept in the 0 to 5V
range; an attenuator may be required.
Coarse Gain is adjusted using the Coarse Gain dropdown menu. The Gain ranges are x2, x4,
x15, x35, x125, and x250. Coarse Gain times Fine Gain equals Overall Gain. After changing
the Coarse Gain value, the Set Gain button will become enabled. Pressing this button will
apply the setting to the Model 970. If an Acquisition is currently underway, it will automatically
pause while the new setting is applied then resume using the new setting.
Fine Gain can be adjusted either by clicking on the slider bar or by clicking the arrow keys to
the right and left of the control. The Fine Gain can be adjusted in 255 steps from
(approximately) x0.004 to (approximately) x1, and the approximate Gain value is displayed
immediately above and to the left. Overall Gain (Coarse Gain times Fine Gain) is displayed
immediately above and to the right. After changing the Fine Gain value, the Set Fine button
will become enabled. Pressing this button will apply the setting to the Model 970. If an
Acquisition is currently underway, it will automatically pause while the new setting is applied
then resume using the new setting.
Use the Fine Gain control to perform small “nudges” to compensate for spectrum drift caused
by temperature changes in the detector. If an even smaller shift in Gain is needed, try
adjusting the High Voltage by tiny increments (including decimal values).
Threshold can be adjusted by either directly entering a number in the Threshold input box or
by using the up/down buttons immediately to its right. When entering the value directly, you
can use any whole number between 0 and 2498 mV. When using the up/down buttons,
Threshold
is increased/decreased in 1 mV increments. After changing the displayed
Threshold value, the Set Thsh button will become enabled. Pressing this button will apply the
setting to the Model 970. If an Acquisition is currently underway, it will automatically pause
while the new setting is applied then resume using the new setting. Note: High values of Gain
will likely necessitate increasing the Threshold.
Shaping Time can be adjusted using the dropdown menu. Possible values are 0.25, 0.5, 1, 2,
4, 6, 8, and 10 µseconds. For the vast majority of cases, a shaping of 1 µsec is appropriate.
After changing the Shaping Time value, the Set S.T. button will become enabled. Pressing
this button will apply the setting to the Model 970. If an Acquisition is currently underway, it
will automatically pause while the new setting is applied then resume using the new setting.
ROI Panel
This displays the ROI Panel, for creating or adjusting ROIs (Regions of Interest). You will not
be able to open this panel until an Energy Calibration has been performed. The intricacies of
this panel are discussed in detail on the next page.