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.
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發表于 2016-3-21 09:40:40
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