Download AMiBA: Automatic Level Control

Array for Microwave Background Anisotropy
Automatic level control
Chia-Hao Chang, Homin Jiang
ASIAA
ASIAA
NTU Physics
Automatic Gain Control :
Correlator temperature control:
The gain was shifted by temperature. We need stable gain when we observer.
We can control the total power by Variable gain amplifier.
Correlator box has many microwave components. Gain fluctuation in a
radio telescope will affect the output signal. We have deployed a simple and
light temperature control system with temperature controller of OMRONE5CN
Total power shifting by temperature
Control the total-power by change the voltage of VGA
450000
Rx4
40
400000
350000
20
200000
150000
100000
10
Total-Power
Total power
250000
400000
Temperature (oC)
30
300000
The tp1 of Antenna 1
The tp1 of Antenna 2
Temperature
Control box(E5CN)
300000
Fan
Tp1
200000
Tp2
100000
0
50000
0
00:00
0
12:00
12
00:00
24
0
0
00:00
48
12:00
36
1
2
3
4
5
6
7
8
9
10
Temperature
sensor
11
VGA(V)
Time
Correlator box
Control box
Testing for gain stability:
We give the system calibration source for reference and feedback control
by PID. To simulate the discrete control which will happen on the site, we
set the observation time is 1 minute, 5 minutes and 10 minutes respectively.
Variable
gain
Amplifier
Calibration
Source
Power detector
Calibration and
control
Observation
Voltage
sensor
ADAM-4024
Install control box on the platform
(voltage control)
Result:
PID running in Computer
Correlator Box:
Target temperature: 25℃
(b) One control in one calibration time
(a) Block diagram of laboratory experiment
Sensor temperature (night): 24.9-25.1 ℃
Electrical Box:
Testing result:
Target temperature: 20℃
Sensor temperature (night): 19.8-20.2 ℃
We set the target voltage is -0.7V. Sampling period is 1, 5, and 10 minutes.
When the temperature drift too much, long sampling period can’t keep the
gain between -0.7V in one control.
Output Voltage
VGA Temperature
Output Voltage
P=0.8, I=150, D=0.1, Interval: 5 minutes
P=0.8, I=30, D=0.1, Interval: 1 minutes
P=0.8, I=300, D=0.1, Interval: 10 minutes
38
-0.065
36
-0.065
36
-0.065
36
-0.07
34
-0.07
34
-0.07
34
-0.075
32
-0.075
32
-0.075
32
-0.08
30
-0.08
30
-0.08
30
-0.085
28
-0.085
28
-0.085
28
26
300
-0.09
26
300
-0.09
0
50
100
150
200
250
0
50
100
150
200
250
Minute
Minute
(a) Sampling is 1 minute
(b) Sampling is 5 minute
Voltage(V)
-0.06
Voltage(V)
38
30
Electrical box
25
Correlator Box
20
ambient
15
10
5
Temperature(V)
-0.06
Temperature(C)
38
-0.09
35
VGA Temperature
-0.06
Temperature(C)
Voltage(V)
VGA Temperature
40
Temperature(C)
Output Voltage
45
0
2007/8/5
12:00
0
50
100
150
200
250
26
300
600000
 Pij   k v
RMS  g pi g pj
2
2007/8/7
12:00
2007/8/8
00:00
2007/8/8
12:00
(c) Sampling is 10 minute
We can get RMS from 3rd section. Total base lines give 21 equations.
The gain of antenna can be calculated by function-a. Then, auto-tuning
the gain to target value.
2
2007/8/7
00:00
Take temperature data during 2007/8/5-8/8.
Minute
Conclusion:
2
B
2007/8/6
12:00
Hilo Time
800000
2
2007/8/6
00:00
2
i
g g
2
j
 s2
---(a)

 K i K j S c2  K i K j S T2  K i S T TSYSi  K i S T TSYSj  TSYSiTSYSj
Total power
700000

500000
400000
Antenna 4
300000
Antenna 5
200000
100000
0
2007/8/12
18:00
2007/8/13
0:00
2007/8/13
6:00
2007/8/13
12:00
2007/8/13
18:00
Hilo Time
There are the total power of Ant.4 and Ant.5.
Conclusion:
By the PID temperature controller, the fluctuation of the temperature
was depressed to ± 0.2 degree Celsius. There are some microwave
components in IF/LO box. Installing the temperature control in IF/LO
box can get more stable gain.