3BSE030220R1 控制器
此应用程序需要120000个计数
这意味着TC520的超范围位必须用作MSB，即17位。温度为0.3ppm/°C的参考电压通常需要在30°C范围内保持稳定。这可能是一项禁止性要求。幸运的是，应变仪的输出灵敏度与施加的电源电压成正比，VSG=K（V+–V–）PSG，eq3/a，其中K是特定应变仪的常数，双斜率转换器产生的结果与其参考电压成反比：TDEINT=VIN TINT/VREF通过从电源电压导出参考电压，任何变化都将完全取消。VREF=RREF x（V+–V–）/RTOTAL eq3/b–VSG=K PSG（V+-V–）G=–RB/RA VIN=（V+？V–）PSG K G RREF=R2B+R3 RTOTAL=R1+R2+R3+R4 VREF=（V+-V–）RREF/RTOTAL TDEINT=VIN VREF TINT=（V+–V-）PSG G K G（V+-V–因此不需要参考参考电压地与使用TC500A的精密基准和应变仪的精密电源不同，将eq3/a和eq3/b组合为eq4可以生成系统的方程式：TDEINT=K G PSG TINT RTOTAL/RREF eq4注意，VIN已被应变仪上的压力（PSG）、应变仪常数（K）和放大器增益（G）的表达式所取代。实际差分参考电压仅由电阻值之比（RTOTAL/RREF）确定。VIN+BUF 7 2 6 9 11 5 4 1 3 TC500A VIN–CAZ CINT VREF+VREF–CREF+CREF–V–模拟公共10 8 VREF接地–5V.68µCINT CAZ RINT+5V VIN R1 R2a R2b R3 R4 6 4 3 2 RA VSG 7 RB–+V–V++应变计PSG–+图3：差动比参考电压。
电容器
AN780 DS00780A第4页©2002 Microchip Technology，股份有限公司.自动调零和参考电容器这些电容器上的电压保持非常恒定，因此不考虑介质吸收。长的积分时间确实需要具有极低泄漏的电容器。两种情况下均使用了0.68µF聚酯电容器。TC520计时已选择200ms积分时间。TC520有几个选项可供选择。可以结合TC520中的两个默认定时中的一个来选择精确的晶体（或时钟速率），或者，可以使用微处理器对TC520进行编程，以获得具有任意晶体频率的适当定时。主要限制是TC500A的比较器延迟约为4µS。此外，TC520在时钟输入上具有除以4的功能。这意味着1MHz左右的任何频率都可以接受。TC520可由微处理器编程，以将实际积分时间设置在约.5ms内。本应用中使用的晶体为1.0703MHz。TC520中有4个时钟/计数，基本积分计数器为256个计数。这计算出使用晶体时的时基周期为0.9567mS。200mS积分时间需要209个时基周期。由于TC520提供了256个时基周期，其中47个需要删除。该值可通过以下等式确定：fOSC x TINT 1024 N=256–=256-1.0703MHz x 200mS 1024=46.957在程序开始时，微处理器被编程为将“47”（2FH）加载到TC520中。这将导致TC500A的积分时间为199.96mS。该值将在50/60Hz时产生至少120dB的抑制。TC520还将使用TC500A自动归零相位的积分定时。17位转换将需要一个解积分时间，该时间是振荡器频率的函数，即217 x 4÷fOSC=490mS。
This application requires 120000 counts
This means that the out of range bit of TC520 must be used as MSB, that is, 17 bits. The reference voltage with a temperature of 0.3 ppm/° C usually needs to be stable in the range of 30 ° C. This may be a prohibitive requirement. Fortunately, the output sensitivity of the strain gauge is proportional to the applied power supply voltage, VSG=K (V+– V –) PSG, eq3/a, where K is the constant of the specific strain gauge, and the result generated by the double slope converter is inversely proportional to its reference voltage: TDEINT=VIN TINT/VREF By deriving the reference voltage from the power supply voltage, any change will be completely cancelled. VREF=RREF x（V+–V–）/RTOTAL eq3/b–VSG=K PSG（V+-V–）G=–RB/RA VIN=（V+？V–）PSG K G RREF=R2B+R3 RTOTAL=R1+R2+R3+R4 VREF=（V+-V–）RREF/RTOTAL TDEINT=VIN VREF TINT=（V+–V-）PSG G K G (V+- V – Therefore, the reference voltage ground is not required. It is different from the precision reference and the precision power supply of strain gauge using TC500A. Combining eq3/a and eq3/b into eq4 can generate the equation of the system: TDEINT=K G PSG TINT RTOTAL/RREF eq4. Note that VIN has been replaced by the expression of pressure (PSG), strain gauge constant (K) and amplifier gain (G) on the strain gauge. The actual differential reference voltage is only determined by the ratio of resistance values (RTOTAL/RREF). VIN+BUF 7 2 6 9 11 5 4 1 3 TC500A VIN – CAZ CINT VREF+VREF – CREF+CREF – V – Analog Common 10 8 VREF Ground – 5V 68 µ CINT CAZ RINT+5V VIN R1 R2a R2b R3 R4 6 4 3 2 RA VSG 7 RB –+V – V++Strain gauge PSG –+Figure 3: Differential ratio reference voltage.
capacitor
AN780 DS00780A Page 4 © 2002 Microchip Technology, Inc Automatic zero setting and reference capacitor The voltage on these capacitors is kept very constant, so dielectric absorption is not considered. Long integration times do require capacitors with very low leakage. 0.68 µ F polyester capacitors were used in both cases. 200ms integration time has been selected for TC520 timing. The TC520 has several options to choose from. The TC520 can be combined with one of the two default timings to select an accurate crystal (or clock rate), or a microprocessor can be used to program the TC520 to obtain an appropriate timing with any crystal frequency. The main limitation is that the comparator delay of TC500A is about 4 µ S. In addition, TC520 has the function of dividing by 4 on the clock input. This means that any frequency around 1MHz is acceptable. The TC520 can be programmed by the microprocessor to set the actual integration time within about. 5ms. The crystal used in this application is 1.0703MHz. The TC520 has 4 clocks/counts, and the basic integral counter has 256 counts. This calculates that the time base period when using crystals is 0.9567mS. The 200mS integration time requires 209 time base cycles. Since the TC520 provides 256 time base cycles, 47 of them need to be deleted. This value can be determined by the following equation: fOSC x TINT 1024 N=256 –=256-1.0703MHz x 200mS 1024=46.957 At the beginning of the program, the microprocessor is programmed to load "47" (2FH) into TC520. This will result in a TC500A integration time of 199.96mS. This value will produce a suppression of at least 120dB at 50/60Hz. TC520 will also use TC500A automatic zero phase integration timing. 17 bit conversion will require a de integration time, which is a function of the oscillator frequency, i.e. 217 x 4 ÷ fOSC=490mS.
