Research And Design Of Temperature Field Measuring Device Based On CAN Bus

In the shape structure of the spacecraft and the recovery test of the aircraft,professional measuring devices are often required to obtain the temperature field distribution characteristics around the spacecraft shell and the temperature information of the key onboard equipment when it is working.High precision,low delay and anti-interference the temperature field measurement device can provide key data support for the optimization of the shape and structure of the aircraft and the condition monitoring of the equipment.Based on domestic and foreign investigations,this subject designs a temperature field measurement device that meets the needs of aerospace experiments.After clarifying the design index,by comparing the traditional temperature field measurement,the design idea of using the compensation wire to extend the thermocouple is used.This project converts the multi-channel temperature acquisition task into multi-node temperature acquisition.The temperature field measuring device includes 1 master measuring device and 5 slave measuring devices.A single measuring device only needs to collect 16 thermocouples,and a communication mechanism of "roll call-response" is established between the measuring devices through the CAN bus to realize the master measurement device for data transfer with and from the slave measuring device.Finally meet the measurement requirements of the temperature field.The master-slave measuring device adopts the same circuit design,and the type of the measuring device is set by downloading different programs.On the hardware circuit,a new general-purpose two-stage temperature measurement circuit integrating thermocouple cold junction compensation and signal conditioning functions is designed,and the acquisition circuit,RS422 interface circuit and CAN interface circuit are designed and analyzed.In terms of software,in order to realize the synchronous 422 communication protocol and the CAN communication application layer protocol,FPGA is selected as the main control,and the C8051 single-chip microcomputer is used as the coprocessor.According to the 422 communication protocol,the encoded temperature field data is sent to the central programmer,and the "roll call" timing is added to the single-chip microcomputer program of the main measuring device and the congestion control mechanism is added to the single-chip microcomputer program of the slave measuring device,effectively avoiding from The communication interruption caused by the abnormal off-line of the measurement device and the network congestion caused by the delayed transmission of CAN data frames improve the reliability of CAN communication.After calibration is complete,several rounds of test verifications have been carried out focusing on the full-scale measurement error of the temperature field measurement device and the stability of the CAN bus.The measurement device can realize signal acquisition of 96 thermocouples,K-type and C-type thermoelectric measurement error of the pair is less than±2°C,and the maximum error is 0.163%F.S.,which meets the device design indicators and can provide reliable data for the structural optimization and flight tests of aerospace equipment.