Atec Agilent-E9320 Series - Manual (Page 10)

Zero set
This specification applies to a ZERO performed when the
sensor input is not connected to the POWER REF.
Zero drift and measurement noise
Effect of averaging on noise: Averaging over 1 to 1024
readings is available for reducing noise. Table 9 provides
the measurement noise for a particular sensor. Use the
noise multipliers in Table 10, for the appropriate speed
(normal or x 2) or measurement mode (normal or average
only) and the number of averages, to determine the total
measurement noise value.
In addition, for x 2 speed (in normal mode) the total mea-
surement noise should be multiplied by 1.2, and for fast
speed (in normal mode), the multiplier is 3.4.
Note that in fast speed, no additional averaging is
implemented.
Example:
E9321A power sensor, number of averages = 4, free run
acquisition, normal mode, x 2 speed.
Measurement noise calculation:
(< 6 nW x 0.88 x 1.2) = < 6.34 nW
Effect of video bandwidth setting: The noise per sample
is reduced by applying the meter video bandwidth reduc-
tion filter setting (High, Medium or Low). If averaging is
implemented, this will dominate any effect of changing the
video bandwidth.
Example:
E9322A power sensor, triggered acquisition, video band-
width = High.
Noise per sample calculation:
(< 180 nW x 0.80) = < 144 nW
Effect of time-gating on measurement noise
The measurement noise will depend on the time gate
length, over which measurements are made. Effectively
20 averages are carried out every 1 us of gate length.
Table 8. Zero set
Sensor model Zero set Zero set
(normal mode) (average only mode)
E9321A, E9325A 5 nW 0.17 nW
E9322A, E9326A 19 nW 0.5 nW
E9323A, E9327A 60 nW 0.6 nW
Table 9. Zero drift and measurement noise.
Sensor
model
E9321A
E9325A
E9322A
E9326A
E9323A
E9327A
Zero drift 1
Normal Average only
mode mode
< ±5 nW < ±60 pW
< ±5 nW < ±100 pW
< ±40 nW < ±100 pW
Measurement noise 2
Normal Normal Average only
mode 3 mode 4 mode
< 6 nW < 75 nW < 165 pW
< 12 nW < 180 nW < 330 pW
< 25 nW < 550 nW < 400 pW
1. Within 1 hour after zero set, at a constant temperature, after a 24 hour warm-up of the power meter.
2. Measured over a one-minute interval, at a constant temperature, two standard deviations, with averaging set to 1
(for normal mode), 16 (for average only mode, normal speed) and 32 (for average only mode, x 2 speed).
3. In free run acquisition mode.
4. Noise per sample, video bandwidth set to OFF with no averaging (i.e. averaging set to 1) - see the note “Effect of
Video Bandwidth Setting” and Table 11.
Table 10. Noise multipliers
Mode
Average
-only
Normal
Number of
averages
Noise multiplier
(normal speed)
Noise multiplier
(x 2 speed)
Noise multiplier
(normal speed;
free run acquisition)
1
5.5
6.5
1.0
2
3.89
4.6
0.94
4
2.75
3.25
0.88
8
1.94
2.3
0.82
16
1.0
1.63
0.76
32
0.85
1.0
0.70
64
0.61
0.72
0.64
128
0.49
0.57
0.58
256
0.34
0.41
0.52
512
0.24
0.29
0.46
1024
0.17
0.2
0.40
Table 11. Effect of video bandwidth on noise per sample.
Sensor
E9321A
E9325A
E9322A
E9326A
E9323A
E9327A
Low
0.32
0.50
0.40
Medium
0.50
0.63
0.63
High
0.63
0.80
1.0
Noise multipliers
10