24
Specification Guide
SR620 Universal Time Interval Counter
TIMEBASE SPECIFICATIONS
The specifications of the timebase affect both the resolution and error of measurements made with the
SR620. A timebase may be specified by two parameters: its short-term stability and its long-term stability.
SHORT-TERM STABILITY
The short-term stability of an oscillator is a measure of the changes in the output frequency of the oscillator on
a short time scale- seconds or less. These changes in the frequency are usually random and are due to
internal oscillator noise, output level modulation,etc. These random changes in frequency affect the resolution
of the measurement just as other internal noise does. The short-term stability of an oscillator is usually
characterized by specifying either its Allan variance or its phase noise. The SR620's timebase short-term
stability is specified by its Allan variance. Typical values for several gate times are:
standard
oscillator oven
oscillator
1.0s
gate
1.2x10
-10
2.3x10
-11
10s
gate
2.3x10
-10
1x10
-11
100s
gate
1.25x10
-9
4.2x10
-11
spec. limit at1s
3x10
-10
5x10-11
The resolution of the SR620 is specified as resolution = ((25ps)
2
+ (time interval x short-term stability)
2
)
1/2
rms
so for time interval greater than 125ms (standard oscillator) or 500ms (oven oscillator) the short-term stability
of the timebase will dominate the resolution limit of the SR620.
LONG-TERM STABILITY
The long-term stability of an oscillator is a measure of its changes in frequency over long time intervals-
hours, days, months, or years. It is the long term stability of the timebase that will ultimately limit the absolute
Graph 1: Differential Non-linearity for time
differences of 0 to 11 ns. This shows the
residual non-linearity of the time-to-amplitude
converters.
Graph 2: Differential Non-linearity for time
differences of 0 to 11ms.
Содержание SR620
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Страница 6: ...iv Table of Contents SR620 Universal Time Interval Counter...
Страница 8: ...vi Safety and Preparation for Use SR620 Universal Time Interval Counter...
Страница 12: ...x Specifications SR620 Universal Time Interval Counter...
Страница 58: ...42 Programming Commands SR620 Universal Time Interval Counter...
Страница 72: ...56 Programming Examples SR620 Universal Time Interval Counter...
Страница 76: ...60 Troubleshooting Tips SR620 Universal Time Interval Counter...
Страница 82: ...66 Performance Test SR620 Universal Time Interval Counter...
Страница 90: ...74 Calibration Procedure SR620 Universal Time Interval Counter...
Страница 102: ...86 Circuit Description SR620 Universal Time Interval Counter...
Страница 124: ...108 Parts List SR620 Universal Time Interval Counter...