Design Of Voltage Dividers Research Articles

Simulation of electron transport and secondary emission in a photomultiplier tube and experimental validation

The electron amplification and transport within a photomultiplier tube (PMT) has been investigated by developing an in-house Monte Carlo simulation code. The secondary electron emission in the dynodes is implemented via an effective electron model and the Modified Vaughan’s model, whereas the transport is computed with the Boris leapfrog algorithm. The PMT gain, rise time and transit time have been studied as a function of supply voltage and external magnetostatic field. A good agreement with experimental measurements using a Hamamatsu R13408-100 PMT was obtained. The simulations have been conducted following different treatments of the underlying geometry: three-dimensional, two-dimensional and intermediate (2.5D). The validity of these approaches is compared. The developed framework will help in understanding the behavior of PMTs under highly intense and irregular illumination or varying external magnetic fields, as in the case of prompt gamma-ray measurements during pencil-beam proton therapy; and aid in optimizing the design of voltage dividers with behavioral circuit models.

Calibration Method of a Wideband AC Resistance Voltage Divider Based on an Equivalent Model.

Aiming at the problem of large measurement error and phase shift in resistance voltage dividers under high-frequency conditions in the field of power measurement, such as power harmonics, an error correction method is proposed for an alternating current (AC) resistance voltage divider based on the equivalence principle. Firstly, the frequency error model of the AC resistance voltage divider precision is established, and the angle difference of the continuous spectrum ratio difference from 50 Hz to 100 kHz is corrected by determining the shielding structure and the resistance parameters and fine-tuning the shielding potential correction method to reduce the capacities error of the AC resistance voltage divider design precision. At the same time, the performance parameters such as the direction and magnitude of the shielding potential compensation capacitive error are investigated. Finally, the precision voltage divider (the maximum voltage applied is 480 V) calibration experiments verify that the important characteristic judgment factor of the voltage divider is independent of the frequency and the equivalent capacitance value, which effectively solves the phase correction problem of harmonic power measurement.

Accurate Numerical Modelling of MV and HV Resistive Dividers

An effective computational tool for the simulation and design of voltage dividers has been realized. It takes advantage of a finite-element procedure for the accurate computation of the divider stray capacitances. These latter are then the input of a circuit solver procedure based on the modified node potential technique, which provides the divider frequency response. Furthermore, a test divider has been set up for the purpose of the tool validation. A very good agreement has been found between measured and computed results. This paper highlights that a correct representation of the resistors is necessary in the finite-element method (FEM) model, during the computation of the stray parameters. This issue has been clarified for the first time in this paper. In addition, a comparison between the FEM and boundary-element method has been carried out before the implementation of the numerical code, stating the superior effectiveness of FEM. The computational tool has been finally tested on a real voltage divider. Good results have been found in terms of computational accuracy. Limited discrepancies between measured and computed results have been found up to 10 kHz, with 5.7% for the scale factor and less than 24 mrad for the phase error.

A gain-programmable transit-time-stable and temperature-stable PMT Voltage divider

A gain-programmable, transit-time-stable, temperature-stable photomultiplier (PMT) voltage divider design is described in this paper. The signal-to-noise ratio can be increased by changing a PMT gain directly instead of adjusting the gain of the preamplifier. PMT gain can be changed only by adjusting the voltages for the dynodes instead of changing the total high voltage between the anode and the photocathode, which can cause a significant signal transit-time variation that cannot be accepted by an application with a critical timing requirement, such as positron emission tomography (PET) or time-of-flight (TOF) detection/PET. The dynode voltage can be controlled by a digital analog converter isolated with a linear optocoupler. The optocoupler consists of an infrared light emission diode (LED) optically coupled with two phototransistors, and one is used in a servo feedback circuit to control the LED drive current for compensating temperature characteristics. The results showed that a six times gain range could be achieved; the gain drift was <0.5% over a 20/spl deg/C temperature range; 250 ps transit-time variation was measured over the entire gain range. A compact print circuit board (PCB) for the voltage divider integrated with a fixed-gain preamplifier has been designed and constructed. It can save about $30 per PMT channel compared with a commercial PMT voltage divider along with a variable gain amplifier. The preamplifier can be totally disabled, therefore in a system with a large amount of PMTs, only one channel can be enabled for calibrating the PMT gain. This new PMT voltage divider design is being applied to our animal PET camera and TOF/PET research.

The development of a detection system for TDPAC studies of 75Se

A fast-slow timing system employing a pair of barium fluoride scintillation counters for gamma—gamma coincidence measurements is currently being developed to enable the binding of 75Se to the protein glutathione peroxidase to be studied using the time differential perturbed angular correlation (TDPAC) technique. Consideration has been given to the need to optimise the system time resolution whilst maintaining reasonable energy resolution. Factors such as scintillator quality, surface treatment, voltage divider design and time pick-off are discussed. The improvements in time resolution realised by making certain changes to the original system are reported.