高精度静电重力梯度仪中远距离低噪声电容位移传感研究

High-precision electrostatic accelerometer is one of the key payloads in the gravity field measurement satellite and low-noise capacitive position sensor is the key technique of the electrostatic accelerometer. The key payload of GOCE satellite is the electrostatic gravity gradiometer which consists of six high-precision electrostatic accelerometers. In order to realize the resolution requirement of mE level gravity gradient measurement, the noise level of single accelerometer must achieve 2×10^(-12)m/s^2/Hz^(1/2)，meanwhile, the thermal stabilization of the gradiometer core which includes the ultrastable carbon-carbon structures and accelerometer sensor head must reach 100 μK level. It is much more rigorous to the position sensor. First, the resolution of the capacitive position sensor must reach the picometer level. Second, it must separate the power consumption circuit far from the gradiometer core to reduce the circuit’s thermal effect, where the thermal control of the circuit is just mK level. It means there must be a long wire between the position transducer and the accelerometer sensor head. So how to reduce the effect of the long wire and to realize the high precision thermal control at the same time must be investigated further. For this problem, the objective of this project is to develop a long-distance which means the position sensor is away from the accelerometer sensor head about 1~3 meters, low-noise capacitive position sensor with the resolution of picometer, equivalent 10^(-7)pF/Hz^(1/2) level. This technique will be applied in higher precision electrostatic accelerometer and the gravity gradient measurement mode gravity satellite missions.

高精度静电加速度计是重力卫星的关键载荷之一，而低噪声电容位移传感是加速度计研究的关键。GOCE卫星中为了实现其核心载荷静电重力梯度仪mE量级的梯度测量指标，要求加速度计的分辨率需达到2×10^(-12)m/s^2/Hz^(1/2)，同时超稳碳碳结构和加速度计敏感探头的热稳定性需达到百μK量级。这对位移传感提出了更严要求，一方面位移检测分辨率需达到皮米量级，另一方面需将发热的电子线路（温控水平仅为mK量级）远离敏感探头以降低其热影响，这意味着传感电路和敏感探头之间会有长距离的导线。如何权衡高精度温控要求与降低长距离导线对位移检测的影响需要深入研究，本项目将针对这一问题，在前期研究工作基础上开展位移分辨率达到皮米量级、等效电容分辨率在10^(-7)pF/Hz^(1/2)量级的远距离（传感电路远离加速度计敏感探头）低噪声电容位移传感研究，为更高精度静电加速度计及其在重力梯度测量卫星中的应用服务。

低噪声电容位移传感是高精度静电加速度计的关键技术之一。针对静电加速度计在重力梯度卫星中的应用，由于梯度仪核心机械单元高精度温控的需求，此时需要有源位移检测电路远离机械单元，因此研制出分辨率达10-7 pF/Hz1/2量级的长距离电容位移传感电路有重要应用意义。.本项目完成的主要研究内容、重要成果和关键数据包括：（1）提出了两种长距离导线传输电容位移传感方案；（2）完成了电容位移传感标定平台研制，其理论标定误差小于1%，并基于此平台分别标定了传感电路的灵敏度系数；（3）验证了高精度电容位移传感电路中传输导线不同接入方式、绕线方式、导线类型、振动干扰和不同温度等对电路性能的影响实验，测试结果表明采用同轴电缆均优于普通导线，绕线方式和振动对前端电路噪声无影响，实验测试结果表明电容分辨率在0.1Hz处均达到10-7pF/Hz1/2量级。.本项目完成了预期研究目标，实现了电容分辨率达到10-7 pF/Hz1/2量级的远距离电容位移传感电路，满足未来重力梯度卫星中高精度静电重力梯度仪对电容位移传感分辨率噪声及敏感探头高精度热控的应用需求。