【導讀】設計采用了單片機AT89C52來實現(xiàn)，硬件部分是以單片機為核心，還包括A/D模數(shù)轉換模塊，顯示模塊，和串行接口部分。該系統(tǒng)下位機負責數(shù)據(jù)采集并應答上位機機的命令。4路被測電壓通過模數(shù)轉換器。MAX232傳輸?shù)缴衔粰C，由上位機負責數(shù)據(jù)的接受、處理和顯示，并用LED數(shù)碼顯示器來顯示所采集的結果。軟件部分應用VB編寫控制軟件，對數(shù)據(jù)采集系統(tǒng)、模數(shù)轉換系統(tǒng)、數(shù)據(jù)顯示、數(shù)據(jù)通信等程序進行了設計。本設計經(jīng)調試完成了數(shù)據(jù)采集、模數(shù)轉換、顯示及上位機繪圖各項功能。[關鍵詞]:數(shù)據(jù)采集;89C52單片機;ADC0809;MAX232;由于這種數(shù)據(jù)采集系統(tǒng)的性能優(yōu)良，超過了傳統(tǒng)的自動檢測儀表和專用數(shù)據(jù)采。該階段的數(shù)據(jù)采集系統(tǒng)采用模塊式結構，根據(jù)不同的應用要求，通過簡。因此能夠開發(fā)出能滿足實際應用要求的、電路結構簡單的、可靠性高的數(shù)據(jù)采集系統(tǒng)。我國的數(shù)字地震觀測系統(tǒng)主要采用TDE-124C型TDE-224C型地震數(shù)據(jù)采集系統(tǒng)。

　　

【正文】 conditioning. Signal conditioning may be more plex. An input signal from a nonlinear sensor may be converted to a voltage that is linear in the quantity being measured, pensation may be made for secondorder effects such as temperature, or an indirect effect such as a frequency shift may be converted to a voltage. Integrated Digitizer As the cost of A/D converters declines, the digitizing function can be moved into the amplifier. For example, the HEKA elektronik EPC9 patchclamp amplifier contains a built in digitizing unit (an Instrutech ITC16). Integrating a digitizer into an amplifier can substantially reduce total noise in the digitized signal, since the analog signal is not carried over a cable from the amplifier to an external digitizer. Be careful of instrument specifications when paring an analog amplifier to one with a builtin digitizer. Including the digital electronics in the amplifier housing may increase noise, and the digitizer itself may add noise to the signal. However, the total noise in the digitized signal may be much less than if an external digitizer is used. Compare an amplifier with an integrated digitizer to the bination of an analog amplifier and an external digitizer. A major advantage of integrating a digitizer into an amplifier is that the amplifier designer can easily include features for puter control. A data acquisition program connected to such an amplifier can then offer an integrated user interface, simplifying operation. In addition, the acquisition program can record all amplifier settings, simplifying data analysis. From Signals to Samples A digitizer consists of an A/D (analog to digital) converter that samples an analog input signal and converts it to a sequence of digital values. Aliasing The sampling theorem states that, in order to be able to reconstruct a signal, the sampling rate must be at least twice the signal bandwidth. What happens if a signal contains ponents at a frequency higher than half the sampling frequency? The frequency ponents above half the sampling rate appear at a lower frequency in the sampled data. The apparent frequency of a sampled signal is the actual frequency modulo half of the sampling rate. For example, if a 26kHz signal is sampled at 50kHz, it appears to be a 1kHz signal in the sampled data. This effect is called aliasing. AntiAliasing Filter If a signal to be digitized has ponents at frequencies greater than the half the sampling frequency, an anti aliasing filter is required to reduce the signal band width. The antialiasing filter must cut off signal ponents above one half the sampling rate. Most signal sources are inherently bandlimited, so in practice, antialiasing filters are often not required. However, some signal sources produce broadband noise that must be removed by an antialiasing filter. For example, patchclamp amplifiers have builtin anti aliasing filters. The pipette used for patchclamp recording inherently filters signals above a low frequency in the range of 1kHz. The good high frequency response of a patch clamp amplifier is achieved only by boosting the high frequency ponent of the signal to pensate for the frequency response of the pipette. This can produce significant highfrequency noise. A patchclamp amplifier provides a filter to eliminate this noise. Integrating Converters The discussion of aliasing assumes instantaneous sampling. The output value produced by the A/D is represents the instantaneous analog signal amplitude. Such sampling A/D converters are the most mon for use in instrumentation. Some A/D converters employ an integrating conversion technique. The output value produced by such a digitizer represents the integral of the analog signal amplitude over the sampling interval. Such converters eliminate aliasing. They can be viewed as containing a builtin antialiasing filter. Integrating converters are rarely used in highspeed control applications. The most mon techniques for implementing highspeed integrating converters result in a delay of many sample intervals between an analog sample and the corresponding digitizer output value. This delay can introduce considerable phase shift at high frequencies in closedloop response if the digitizer is used in a control system. Resolution Typically a digitizer provides the puter with fixed length binary numbers. For example, the Axon Instruments Digidata 1200A produces 12bit numbers, while the Instrutech Corporation ITC16 produces 16bit numbers. The length of each value is called the resolution of the device, measured in bits. The resolution can be translated to an absolute input level. Most digitizers measure swings of up to approximately 10V from zero, for a total range of 20V. A 12bit value has a resolution of 1 part in 4096, so the resolution of a 12bit digitizer is 20V divided by 4096, or approximately 5mV. This is expressed by saying that a change of one count (or one least significant bit, or LSB) represents 5mV. 8 b i t s1 0 b i t s1 2 b i t s1 4 b i t s1 6 b i t s1 8 b i t sD i g i t i z e r R e s o l u t i o n ( + 1 0 V R a n g e )R e s o l u t i o nD i s t i n c t V a l u e s1 L S B( a p p r o x i m a t e )2 5 61 0 2 44 0 9 61 6 3 8 46 5 5 3 62 6 2 1 4 48 0 m V2 0 m V5 m V1 . 2 5 m V3 0 0 μ V7 5 μ V Since analog instruments rarely have an accuracy significantly exceeding %, it might seem that 10 or 11 bit resolution would be sufficient in a digitizer. However, additional bits of resolution are needed because the input signal frequently does not use the entire input range. For example, even if the instrumentation amplifier gain has been adjusted to yield an input signal with a 20V range, small ponents of the signal with a 2V range might also be of % resolution of a 2V signal within a 20V range requires a