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Pt100是一种公认的高精度测温标准传感器,其物理、化学性质都非常稳定,具有精度高、稳定性好、性能可靠的特点[8]。Pt100的电阻和温度成一定函数关系,被广泛应用于−200~850 ºC范围内的温度测量,可测固体、液体、气体等多种形态物体的温度。在理想情况下,其电阻阻值与温度关系式如式(1)所示:
式中:A = 3.908 02×10−3;B = −5.775×10−7;C = −4.183×10−12;R0为Pt100在0 ºC时的电阻值,为100 Ω;T为摄氏温度;RT为T温度时对应的电阻值[9-11]。
本设计根据Pt100的温度-阻值函数关系,通过对其阻值的测量来监测锗晶体的温度变化。从表1可以看出,Pt100的温度-阻值变化率很小,只有0.4 Ω/ºC左右,环境噪声会对输出结果造成很大影响。假如只以−163 ºC单一阈值作为触发通/断的标准,就要求保护装置具有极高的采样精度和灵敏度。为了降低设计成本并提高保护装置的可靠性,在选择触发保护的高阈值温度时保留2 ºC的余量,即在温度达到−165 ºC时输出控制信号,使高压模块切断高压输出。当锗晶体温度低于−170 ºC时,真空腔内由于没有游离粒子即可触发恢复施加高压,所以触发恢复高压的低阈值温度选择−170 ºC。5 ºC的阈值差提高了系统分辨能力,也为探测器提供了缓冲空间。由表1可知高低阈值温度对应的阻值变化仅2 Ω左右。同时,Pt100的工作电流要小于5 mA,所以,如何精确地采集到Pt100的阻值的变化以及提升系统抗干扰能力是本设计的难点所在。
T/ºC −170 −169 −168 −167 −166 −165 −164 −163 RT/Ω 31.28 31.70 32.12 32.54 32.96 33.38 33.80 34.22 -
HPGe探测器高压控制方案如图1所示,其中锗晶体浸泡在充满液态氮的腔体内,Pt100与锗晶体处于相同的环境,通过接头引线至高压模块控制器,进行阻值采样。高压模块的输出接口(CH)和探测器高压输入接口相连,高压模块选用CAEN公司的N1470高压模块,该模块的高压输出通过硬件接口INTLcK控制。当接口的1和2、3和4引脚短路时,高压模块内部处于锁定状态,停止高压输出。当接口的1和2引脚断路、3和4引脚短路时,高压模块内部会自动解锁,恢复高压输出。控制方案中利用跳线使3和4引脚保持短接,通过高压模块控制器来控制1、2引脚的接通和断开,以达到控制高压模块切断和恢复输出高压的目的[12]。
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测试系统如图11所示,利用上海正阳仪表厂ZX92A直流电阻箱代替Pt100进行高压模块控制器的测试,该电阻箱阻值范围0~1 111.10 Ω,准确度为0.1%,调节步进0.01 Ω。高压模块控制器输出利用万用表的通断测试功能进行测试。上位机通过USB转串口线缆与高压模块控制器相连,利用串口调试助手进行指令的发送和接收。
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每个通道的高低阈值初始值通过试验获取,并作为状态寄存器模块中各通道高低阈值的初始值。将电阻箱的阻值分别设定为31.28和33.38 Ω,接入每个通道,通过上位机发送读取通道采样值指令,获得每个通道的高低阈值,该高低阈值为进行了均值滤波、增益和零点漂移校正后的结果,如表2所列。
通道 低阈值 测量电压(低阈值)/V 高阈值 测量电压(高阈值)/V CH0 E2FD 4.433 41 F1BE 4.721 53 CH1 E2FE 4.433 39 F1BD 4.721 50 CH2 E2FD 4.433 40 F1BE 4.721 52 CH3 E2FC 4.433 38 F1BD 4.721 49 CH4 E2FD 4.433 41 F1BC 4.721 48 CH5 E2FE 4.433 40 F1BD 4.721 50 CH6 E2FC 4.433 36 F1BE 4.721 51 CH7 E2FD 4.433 39 F1BC 4.721 49 -
对高压模块控制器的功能进行测试。电阻箱的阻值由小到大再由大到小变化,变化范围为30.50~34.00 Ω,考察高压模块控制器的输出是否满足设计要求,具体测试如表3所列。
通道 低阈值触
发阻值/Ω对应温度
(低阈值)/ºC高阈值触
发阻值/Ω对应温度
(高阈值)/ºCCH0 31.12 −170.24 33.37 −165.12 CH1 31.13 −170.25 33.34 −165.17 CH2 31.14 −170.29 33.35 −165.11 CH3 31.14 −170.29 33.36 −165.11 CH4 31.12 −170.26 33.33 −165.13 CH5 31.13 −170.26 33.37 −165.12 CH6 31.15 −170.29 33.34 −165.16 CH7 31.15 −170.28 33.32 −165.11
Design of Multi-channel High Voltage Protection System for High Purity Germanium Detector
doi: 10.11804/NuclPhysRev.40.2023017
- Received Date: 2023-02-21
- Rev Recd Date: 2023-04-08
- Available Online: 2024-02-04
- Publish Date: 2023-12-20
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Key words:
- high purity germanium detectors /
- high voltage protection /
- Pt100 Sensor /
- analog-to-digital converter /
- FPGA
Abstract: High purity germanium detectors are widely employed for gamma ray measurements in nuclear spectroscopy experiments at the moment. The application of high voltage during operation necessitates stringent monitoring and control conditions. Traditional manual observation-based monitoring methods prove inefficient and slow in response, often resulting in varying degrees of detector damage. To address this issue, real-time temperature changes in the high purity germanium detector are converted into resistance value measurements using Pt100 sensors. Subsequently, a high-voltage module controller is designed and implemented to establish a protection system for the high purity germanium detector's high voltage supply. The hardware and logic of the controller are meticulously designed, while noise reduction algorithms are studied to enhance performance. Finally, circuit tests validate that the developed system automatically cuts off the high voltage when the detector temperature exceeds an upper threshold and restores it when the temperature falls below a lower threshold. This system effectively meets real-time protection requirements for high-voltage applications with respect to high purity germanium detectors.
Citation: | Jingzhe ZHANG, Wenkai LI, Xiaorui WANG, Linbo MA, Bo ZHANG, Jinfeng XIAO, Meiyang LIU, Xiangxiang GOU, Jiuyao ZHAO, Chengcheng SHI. Design of Multi-channel High Voltage Protection System for High Purity Germanium Detector[J]. Nuclear Physics Review, 2023, 40(4): 589-598. doi: 10.11804/NuclPhysRev.40.2023017 |