Research On Real-time Decoding And Control System For Signals Of Motion Position Sensor At Beamline Station

The synchrotron radiation experiment at SSRF(Shanghai Synchrotron Radiation Facility)requires the beamline station system to support high real-time on-the-fly mode.The core is to develop a system between the motion control subsystem and the data acquisition subsystem.It could decode signals of motion position sensor and output trigger control signals in real time,named the real-time decoding and control system for signals of motion position sensor.It is the link between motion position sensor signal decoding and actuator control,which could greatly shorten the beamline station experiment time and realize the conversion from step-by-step to on-the-fly mode.The system is designed with modular hardware and software subsystems.Specifically,it supports subsequent upgrades,multi-voltage domain signal processing,and other features.Also,the RTL(Register Transfer Level)subsystem in the FPGA(Field Programmable Gate Array)chip is highly scalable.The system,implemented on a programmable FPGA chip,is designed to process multi-channel signals of the different high-precision motion position sensor with a noise background in real time.For high-precision QID(Quadrature Incremental Decoding Motion Position Sensor)signals,the system applies a digital filter based on LFSR(Linear Feedback Shift Register)to adjust the low-pass band frequency of multichannel signals through an ? matrix.The identification and correction method is used to distinguish features between QID signal and noise signal.Meanwhile,the redundancy counting method uses 4 times counting to reduce errors.The system is also designed with an SSI(Synchronous Serial Interface)signal parser for decoding the SSI absolute value motion position sensor signals.The decoding of QID signals has high real-time performance and each decoding channel has a fixed delay time,while the SSI absolute value motion position sensor and its parser are more focused on the accuracy of the position information.The system outputs a real-time trigger control signal according to the decoding value of motion position sensor and configuration data,plus a preset single or multichannel increase/decrease self-trigger mode.When working in the outer trigger mode,the system responds to the external trigger signal with rising edge feature,and stores the decoding value of motion position sensors in the FIFO(First In First Out)at the corresponding time.After the work ends and the system receives the read command from the user,the data in the FIFO is read out and stored in the SD(Secure Digital)card.The test and experimental results show that the real-time decoding and control system could detect multi-channel QID signals in parallel with an SNR(Signal Noise Ratio)of 1:1.The overall error rate is less than 0.5% when the filter parameter ? is between 8 and 250.For a QID signal with a frequency between 25 kHz and 800 kHz,? values range from 8 to 11 and the error rate is less than 0.05%.The QID signal decoding time for each channel is proportional to ?,3?+3 sampling clock cycles.And the system has a real-time performance.