7
resolution of the null measurement.
The actual
meas urement
of
linearity is
accomplished by dialing the Pulse Height dial to 0,
resulting in the amplifier output being reduced to
zero. Since the Pulser supplies s ignals in parallel
both to the bridge for null and to the amplifier,
varying the Pulser output will have no effect on the
null if perfect amplifier linearity is assumed.
As an ex ample of this method, assume that the
amplifier under test has essentially zero output
impedance. Set R1 equal to 100
Ù
and R2 equal to
200
Ù
. Let diodes D1 and D2 be 2N2048 connected
as diodes. Only one-half of the actual amplifier
output voltage can be measured directly at point A
due to the superposition of the outputs of the Pulse
generator via R1 and the amplifier via R2. To specify
nonlinearity as a percentage of full Output voltage,
the calibration of 10 mV/cm will be equal to 10 mV/5
V or 0.2% per cm. Therefore it is seen that 0.1% is
quite easily resolved.
In addition to linearity measurements, it is obvious
that this method can be quite useful in
measurements of temperature stability.
Pulse Height Analyzer Calibration
With the
Pulser calibrated to read directly in terms of energy
as described earlier in this section, the calibration of
a complet e spectrometry system from preamplifier
to multichannel analyzer, i.e., analog to digital
convert er (ADC), can readily be accomplished by
simply feeding into the preamplifier a calibrated
energy signal and observing the corresponding
channel into which it is assigned by the ADC.
An important consideration in this test involves
ensuring that the linear system "goes through zero,"
and that the output of the pulse generator is properly
terminated. The attenuator switches in the 480 have
an accuracy controlled by 1% metal film resistors
and could be used to digitally check the linearity of
the spectrometer. In addition to the attenuator
accuracy, the Pulse Height control has independent
integral nonlinearity of ±0.25%. This control
therefore allows an integral linearity curve of the
ADC to be taken over the continuous range of the
ADC, i.e., from zero to the maximum address of the
ADC. Due to the better integral linearity control,
continuous scanning with the Pulse Height control is
the recommended method of c hecking for system
linearity. The linearity of the ADC can therefore be
determined by having previously taken the linearity
curve of the amplifier and preamplifier as outlined
earlier in this section.
5. MAINTENANCE
5.1. TESTING PERFORMANCE OF THE
PULSER
The following information is intended as an aid in
the ins t allation and checkout of the 480. These
instructions present information on front panel
controls , waveforms at test points, and output
connectors.
The following, or equivalent, test equipment is
needed:
Tektronix Model 580 Series Oscilloscope
100
Ù
BNC Terminators
Vacuum Tube Voltmeter
Before testing the performance of the 480, take the
following preliminary steps:
1. Visually check the module for possible damage
due to shipment.
2. Connect ac power to NIM-standard Bin and
Power Supply, 0RTEC 401 /402.
3. Plug module into Bin and check for proper
mechanical alignment.
4. Switch ac power on and c heck the dc Power
Supply voltages at the test points on the 402.
The performance test consists of the following:
1. Set the front panel controls on the 480 as follows:
a. relay switch to On,
Содержание ORTEC 480
Страница 6: ...vi ...
