| Prompt gamma neutron activation analysis technology is an on-line analysis technology that has the characteristics of real-time online,non-destructive,and multi-element simultaneous measurement,and has become the best choice for real-time inspection and analysis of large-scale industrial materials.This technology has a wide range of applications in the coal industry,cement industry,steel industry and other fields.The developed countries in Europe and the United States started their studies relatively early and developed a mature industrial chain and related products.However,the research in this field in our country started late.With the development of industrial technology,the demand for on-line analysis of material composition is also increasing.In 2013,the Ministry of Science and Technology of China launched a special study on national major scientific instruments and equipment based on the real-time online detection system for industrial materials based on gamma neutron activation analysis technology.Our group is responsible for one of the sub-tasks—the development of a high counting rate electronic system.This research has achieved phased results.The prototype system has been developed and started testing in industry field.When the prototype system testing in industry field,it suffers complex working conditions and faces the following problems.Firstly,the baseline is affected by the site environment and is unstable,which will affect the resolution.Secondly,the photomultiplier tube voltage divider circuit is unstable and the detector output signal fluctuates greatly.Finally,prototype systems need to further reduce costs in order to promote industrialization.In view of the above issues,this article proposes several solutions and conducts feasibility demonstrations on the plans to determine the final prototype upgrade plan.Based on the prototype upgrade program,the main circuit of each part of the system was upgraded and designed,and corresponding testing work was conducted.For the problem of baseline instability,based on the principle of baseline recovery,this paper proposes a gating circuit design that can control and switch the working state of the photomultiplier tube under the condition that the photomultiplier tube is subjected to high voltage,so that the baseline and the signal are separately measured.Then baseline is restored by digital methods.For the problem of voltage instability in voltage divider circuits,this paper proposes an improved design that using high-precision resistors with the same temperature coefficient for voltage regulation instead of using zener diodes.The improvement is tested for optimal resolution in different detectors by changing the voltage divider ratio.This article presents an integrated chassis design,replacing the PXI chassis of the prototype system,and based on the capabilities of the prototype system,further reduce costs and promote industrialization.The innovations in this paper mainly include the following points:1)Propose a fast gating design of photomultiplier tube voltage divider circuit for baseline restoration.MOS transistor is used to control the level of the first dynode by controlling the conduction state of the MOS tube,so as to realize the control of the working state of the photomultiplier tube and realizing the independent measurement of the baseline and the signal.2)A high-precision resistance regulation scheme is proposed for voltage stablility.By selecting resistor elements with the same temperature coefficient,the voltage instability of the photomultiplier tube voltage divider circuit is less than 0.5%.3)An integrated chassis was designed to replace the PXI chassis system.Data was transmitted using the Ethernet bus.The electronics design of the prototype system was completely upgraded and replaced,and the application requirements of the composite industrial site were tested. |
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