Development Of Multifunctional Cryogenic Resistance Measuring Instrument

Last few years, Along with the research and the development of low temperature environment, People discovered much startling phenomenon through the low temperature environment, such as Low temperature superconductive phenomenon, Currently is widely used in the field of the Electronics, Biomedical science, Transportation, the Electric Power Delivers and interrelated range of Sensor-based system. The emphasis is put on sensitivity, precision and automatic, In the research of many low temperature techniques and the low temperature physics phenomenon. All include the curve analyse of temperature and resistance measuring of sample. How to measure accurately the change of resistance relative with the temperature variety has already become an important topic in the realm of low temperature measurementThis paper is mainly about the problem of low temperature resistance measurement. This system uses the AT89C52 as the CPU of the instrument, the MAX110 as the core of data acquisition circuit. I exploit the multifunctional cryogenic resistance Measuring Instrument. The data of measured were send out through the serial communication controller to PC, so the resistance parameters can be measured by automatic.This paper introduces the multifunctional cryogenic resistance Measuring Instrument by means of hardware and software structure. The hardware system mainly includes the AT89C52 as the core of main control circuit, The MAX110 as the core of data acquisition circuit, Collection circuit of resistance signal, Collection circuit of temperature signal, Serial communication controller circuit, Commutator circuit of constant - current source etcThe main control circuit is used the AT89C52 which made by the ATMEL company as the microprocessor of the instrument. It is extensively applied in various control realm. It include reset circuit and clock circuit, We can make use of the RTS of serial communication to sent out the effective signal to reset the main control circuit. In order to increase the metrical precision, avoid the infection of thermoelectromotive force and contact electromotive force, We designed the commutator circuit of constant - current source. Pin PI.4 and PI.5 of AT89C52 to control the current of constant - current source to resistance measuring of sample or Pt resistance. For the measurement of temperature, We adopt resistance temperature detector( short for RTD ). In numerous methods of measurement, RTD is the most accurate. The method is let the current pass resistance and measure its voltage. The Pt is a kind of metal can be purify very much, And the function of the Pt resistance is very stable, The sensor of this system is use the Pt resistance, Its resistance about 100Q, When the current passed were 1mA, the voltage of his both ends about lOOmV, That is very fit to measure. Collection circuit of resistance signal Adopt the same way with collection circuit of temperature signal. We adopt two stage to amplified voltage of resistance signal. The first stage amplifier is apply the chopper-stabilized amplifier ICL7650, the second stage amplifier is amplified by OP07. P1.0 of AT89C52 control electrical relay on state or cut off state. We can let the circuit working at the emitter follower amplifying status or the same phase input amplifying status. If the voltage signal we measured is very strong then let the second stage amplifier working on the emitter follower amplifying status. The voltage signal amplified by the first stage amplifier and the emitter follower sent directly to the A/D convert circuit. If signal we measured is weak voltage, In order toimprove the precision of the measurement, we let the second stage amplifier working on same phase input amplifying status. The weak signal not only amplified by The first stage amplifier circuit but also by the second stage amplifier circuit and then sent to the A/D convert circuit. The core of data acquisition circuit is MAX110, which has two channel and 14-bit A/D converter. The data of temperature was sent to the channel 1 and the data of resistance was sent to the channel 2. The singles is passed to microcomputer after A/D converted and it can be calibrated by software and hardware. All artificial circuit and microcomputer is isolated with photocoupler. The low-frequency control lines use TPL521, the high ones use 6N137. Isolation circuit restrains the keen-edged impulse and other kinds of noise, and increases the radio of signal. Low cost MAX232 is used in the serial communication controller circuit, function of which is to convert voltage from TTL to RS232 and communicate with PC. Therefore the multifunctional cryogenic resistance Measuring Instrument not only can send the data to PC, but also can receive control order come from PC.The host machine's software is program by assembly language, which can automatic control the host. The procedure includes the main program segment, the initialization program segment, the A/D convert program segment, microcomputer recepte and execut order program segment, the key interrupt program segment, the serial port interrupt program segment, data communication program segment and data-processing program segment.The instrument' PC software is program by VB 6.0 .VB has the friendly interface and easy method for program, The controls not only reduce the tedious of program, but also provide the method to build the virtual apparatus interface. So the user oriented system can be build.By the experimental verification, this system operates well. It has high accuracy to the curve analyse of temperature and resistance measuring of sample.