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電子工程網

標題: 直流納伏以下放大器 [打印本頁]
作者: 泓睿    時間: 2016-3-21 09:40
標題: 直流納伏以下放大器
詳細介紹：
EM A20是一種可以對毫微伏進行測量的敏感的放大器。根據設計，它被用在校準、低溫研究和儀器系統內。
A20的生產是為了滿足EM零位探測器內儀器具備類似靈敏度的要求。它的短路輸入很低，等同于低于10Ω的噪聲阻抗，借助很短的響應時間給出了100μV的解決方案。
對于A20能夠運行的電源電阻范圍，我們給與了特別關注。對于電源電阻針對噪聲電壓波形，我們開展了研究。這一研究表明了它的重要性。“電流”和“電壓”噪聲線路從300K被外推至3K。當A20處于室溫條件下時，它可以在氮點下對電源進行有效的測量，同時又不提高噪聲水平。
從1×102至1×106之間，存在著4種增益設定。借助25條渠道的D型連接，施加各種等級的電壓，以選擇各種增益設定。這種D型連接可以對濾波器進行控制，并能連接輸出，提供電源并發揮其他的作用。在有要求的情況下，讓用戶對增益設定進行定義是可能的。在這種情況下，在外部安裝增益設定阻抗，用戶也能對其實施控制。4個增益控制線路保持開路，增益阻抗也在連接器上的點10和11之間連接。
在機箱邊緣可以接入控制器，以將補償電壓和電流清零。輸入連接在銅制終端之上，螺帽和墊圈都由相同的高純度銅支撐，因此熱電勢效應就被最小化了。
A20被安裝在一個重型高導磁率合金內，輸入單元被裝在一個重型計量高導磁率合金雙屏之中。
The EM model A20 is a very sensitive amplifier for making sub nanovolt measurements and is designed to be used in calibration, cryogenic research and instrumentation systems.
The A20 has been produced in response to requests for an amplifier of similar sensitivity to those used in EM null detectors, having a very low short circuit input equivalent noise resistance of less than 10 ohms, giving resolution of a hundred picovolts with comparatively short response time.
Particular care has been taken with respect to the range of source resistance with which the A20 can operate. This parameter is very important when measuring cryogenic sources. A study of the graph overleaf of source resistance against noise voltage will show the importance of this. The `voltage' and `current' noise lines have been extrapolated from 300 deg K to 3 deg K. and it can be seen that the A20, while remaining at room temperature can efficiently measure a source at helium temperature, without adding significantly to the overall noise.
There are 4 gain settings from a thousand to a million and these are selected by voltage levels applied via the 25 way `D' type connector, which has a control for a filter, as well as carrying the output connection, the power supply and other functions. It is possible to have user defined gain settings if required, in which case the gain determining resistors are mounted externally and are under the user抯 control. The four gain control pins are left open circuit and the gain resistor is connected between pins 10 and 11 on the 慏&O5533; connector.
Controls are accessible at the edge of the case for nulling offset voltage and current.
The input connections are made on copper terminals with nuts and washers all made from the same high purity copper, so that thermal emf is minimised.
The A20 is mounted in a heavy duty mumetal case, and the input unit is enclosed in double
screens of heavy gauge mumetal.


A20型直流毫微伏放大器

噪聲：

同等的噪聲阻抗低于10Ω。噪聲電壓取決于帶寬，也就是，上升時間為恒定的10秒，峰峰噪聲電壓為250nVp-p。
Noise.
Equivalent noise resistance less than 10 ohms. Noise voltage depends on bandwidth e.g. rise time constant 10 seconds gives peak to peak noise voltage of 250 picovolts.


補償電壓

借助在機箱邊緣帶有10個刻度的電位計將電壓調整為0度。溫度系數優于300pV/℃。
Offset Voltage.
Adjustable to zero by a ten turn potentiometer accessible at the the edge of the case. Temperature coefficient better than 300pV per degree C.


補償電流

借助在機箱邊緣帶有10個刻度的電位計將電壓調整為0度。溫度系數優于10pV/℃。
Offset Current.
Adjustable to zero by a ten turn potentiometer accessible at the edge of the case. Temperature coefficient better than 10pA per degree C.
增益


有4個增益設定，分別為1000,10000,100000,1000000。這些增益在內部設定，精確度為0.02%，取決于本底噪聲。溫度系數為5ppm/℃。
Gain.
There are 4 gain settings 1K, 10K, 100K, and 1M. These gains are set internally.
Accuracy 0.02%, subject to noise floor.
Temperature coefficient 5ppm per degree C.


濾波器

可以選擇一個能夠給出下列上升時間常數的濾波器。
Filter.
A filter may be selected which gives the following rise time constants.


范圍 時間常數

1000: 無增加

10000: 100毫秒

100000: 1秒

1000000: 10秒
Range     Time Constant
1K:          No Increase
10K:        100 milliseconds
100K:      1 second
1M:         10 seconds


輸入阻抗

在階躍輸入函數3秒之后，大于30000000Ω。隨著時間增長到1GΩ，參見輸入阻抗圖。
Input Impedance.
Greater than 30 Megohms, 3 seconds after an input step
increasing with time to 1 Gohm, see input impedance graph


電源電阻

A20嚴格遵循電源熱噪聲特性，電源阻抗的范圍在10Ω到100000Ω之間。當阻抗低于10Ω時，噪聲便會不斷下降，使得阻抗最后低至0Ω。當電阻在1000000Ω之上時，噪聲電壓將上升至熱噪聲特性之上，上升幅度為10進制的10dB。輸入噪聲特性圖展示，如果“電壓”和“電流”噪聲線被推出，那么A20將使得總體噪聲水平提升大約1K源電阻。
Source Resistance.
The A20 closely follows the source thermal noise characteristic
with sources resistances of 10 ohms up to around 100 Kohms.
With source resistances below 10 ohms, the noise is substantially
constant down to zero ohms. Above 100 Kohms, the noise voltage
increases over the thermal noise characteristic by about 10 dB per
decade of source resistance. The input noise characteristic graph
shows that, if the `voltage' and `current' noise lines are
extrapolated as far as the thermal noise line for helium
temperature, the A20 still adds insignificantly to the total noise at
around 1K source impedance.

輸入等級

A20可接受的輸入電壓高達2mV。高達2V的輸入電壓將不會造成損害，如果輸入電壓在任意時間段出現飽和現象，那么將會出現熱補償的情況，因此需要一定的時間以降低到nV的等級。
Input Level.
The A20 will accept input voltage up to 2mV. Input voltage up to 2
volts will not cause damage, but if the input is saturated for any
length of time, there may be a thermal offset, which could take
time to reduce to sub nanovolt levels.


輸出等級

A20將提供一個±3V的輸出，并將載荷提高至5mA.
Output Level.
The A20 will provide an output of plus or minus 3 volts and can
drive loads of up to 5mA.


連接器

A20的輸入連接器為純銅終端，帶有同樣材質的螺帽和墊圈。螺紋為2BA（直徑為4.8毫米）。

應當使用低熱電磁場未鍍錫的銅線實施輸入連接工作。在實際工作中，新的、未彎曲的、被細致剝除絕緣的變壓器線可滿足要求。
Connectors.
The input connectors for the A20 are pure copper terminals with
nuts and washers made from the same material. The threads are
2BA (4.8mm diameter)
Input connections should be made using low thermal emf untinned
copper wire. In practice, new, unbent transformer wire,
carefully stripped of insulation, is satisfactory.


D25 插頭連接

插頭功能

1、濾波器

2、增益 1M

3 、增益 100K

4 、增益 10K

5 、增益 1K

6 0v

7 電源負壓

8 電源正壓

10 直接輸出

11 反饋

15 濾波輸出

18 信號 0V

19 機箱

插頭外罩被連接至A20機箱。

機箱和0v.之間的絕緣最小為10GΩ。

為了對增益和濾波功能實施控制，應當將選定的銷釘連接至+5V。

所有未使用的銷釘應當保持開路。
D25 Plug Connection.
Pin Function
1 Filter
2 Gain 1M
3 Gain 100K
4 Gain 10K
5 Gain 1K
6 0v
7 Supply Negative
8 Supply Positive
10 Direct Output
11 Feedback
15 Filtered Outpu
18 Signal 0v
19 Case
The plug outer shield is connected to the A20 case.
Isolation between case and 0v. 10 Gohms minimum.
For control of gain and filter functions, the appropriate pin should
be connected to + 5 volts.


電源

最小 ± 5.5 V， 最大 ± 8 V。

常規電源± 6 V。

靜止電流要求 1.5mA。

當放大器在 1K的范圍且出現全刻度輸入的情況時，電流要求可以提高至4mA。
Power Supply.
Minimum +/- 5.5 volts. Maximum +/- 8 volts.
Nominal supply voltage +/- 6 volts
Current requirement 1.5 milliamps quiescent.
This may increase up to 4 milliamps when the amplifier sees a full
scale input on the 1K range


固定

要求M4中心設有4個洞，尺寸為8.4英寸和5.6英寸。
Fixing.
4 holes required M4 centres 8.4 inches by 5.6.inches.


規格和重量

長度 8.75英寸(222毫米)

寬度 6 英寸 (152.4毫米)

包含終端的深度 3.7 英寸(毫米)

重量 9 磅 (4 Kg)
Dimensions and Weight.
Length 8.75 inches (222mm)
Width 6 inches (152.4mm)
Depth including terminals 3.7 inches (95mm)
Weight 9 lbs (4 Kg)
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