công cụ tìm kiếm bảng dữ liệu linh kiện điện tử |
|
ADVFC32 bảng dữ liệu(PDF) 6 Page - Analog Devices |
|
ADVFC32 bảng dữ liệu(HTML) 6 Page - Analog Devices |
6 / 7 page REV. B ADVFC32 –5– application of Figure 2, a 10 ppm/ °C input resistor used with a 100 ppm/ °C capacitor may result in a maximum overall circuit gain drift of: 100 ppm/ °C (ADVFC32BH) + 100 ppm/°C (C1) + 10 ppm/ °C (R IN) = 210 ppm/ °C Although RIN and C1 have the most pronounced effect on tem- perature stability, the offset circuit of resistors R4 and R5 may also have a slight effect on the offset temperature drift of the circuit. The offset will change with variations in the resistance of R4 and supply voltage changes. In most applications the offset adjustment is very small, and the offset drift attributable to this circuit will be negligible. In the bipolar mode, however, both the positive reference and the resistor used to offset the signal range will have a pronounced effect on offset drift. A high quality refer- ence and resistor should be used to minimize offset drift errors. Other circuit components do not directly influence temperature performance as long as their actual values are not so different from nominal value as to preclude operation. This includes integration capacitor C2. A change in the capacitance value of C2 results in a different rate of voltage change across C2, but this is compensated by an equal effect when C2 is discharged by the switched 1 mA current source so that no net effect occurs. The temperature effects of the components described above are the same when the ADVFC32 is configured for negative or bipolar input ranges, or F/V conversion. OTHER CIRCUIT CONSIDERATIONS The input amplifier connected to Pins 1, 13, and 14 is not a standard operational amplifier. Although it operates like an op amp in most applications, two key differences should be noted. First, the bias current of the positive input is typically 40 nA while the bias current of the inverting input is ±8 nA. Therefore, any attempt to cancel input offset voltage due to bias currents by matching input resistors will create worse offsets. Second, the output of this amplifier will sink only 1 mA, even though it will source as much as 10 mA. When used in the F/V mode, the amplifier must be buffered if large sink currents are required. MICROPROCESSOR OPERATED A/D CONVERTER With the addition of a few external components the ADVFC32 can be used as a ±10 V A/D microprocessor front end. Although the nonlinearity of the ADVFC32 is only 0.05% maximum (0.01% typ), the resolution is much higher, allowing it to be used in 16-bit measurement and control systems where a mono- tonic transfer function is essential. The resolution of the circuit shown in Figure 5 is dependent on the amount of time allowed to count the ADVFC32 frequency output. Using a full-scale frequency of 100 kHz, an 8-bit conversion can be made in about 10 ms, and a 2 second time period allows a 16-bit measurement, including offset and gain calibration cycles. As shown in Figure 5, the input signal is selected via the AD7590 input multiplexer. Positive and negative references as well as a ground input are provided to calibrate the A/D. This is very important in systems subject to moderate or extreme temperature changes since the gain temperature coefficient of the ADVFC32 is as high as ±150 ppm/°C. By using the calibration cycles, the A/D conversion will be as accurate as the references provided. The AD542 following the input multiplexer provides a high impedance input (10 12 ohms) and buffers the switch resistance from the relatively low impedance ADVFC32 input. If higher linearity is required, the ADVFC32 can be operated at 10 kHz, but this will require a proportionately longer conversion time. Conversely, the conversion time can be decreased at the expense of nonlinearity by increasing the maximum frequency to as high as 500 kHz. HIGH NOISE IMMUNITY, HIGH CMRR ANALOG DATA LINK In many applications, a signal must be sensed at a remote site and sent through a very noisy environment to a central location for further processing. In these cases, even a shielded cable may not protect the signal from noise pickup. The circuit of Figure 6 provides a solution in these cases. Due to the optocoupler and voltage-to-frequency conversion, this data link is extremely insensitive to noise and common-mode voltage interference. For even more protection, an optical fiber link substituted for the HCPL2630 will provide common-mode rejection of more than several hundred kilovolts and virtually total immunity to electrical noise. For most applications, however, the frequency modulated signal has sufficient noise immunity without using an optical fiber link, and the optocoupler provides common-mode isolation up to 3000 V dc. Figure 5. High Resolution, Self-Calibrating, Microprocessor Operated A/D Converter |
Số phần tương tự - ADVFC32_17 |
|
Mô tả tương tự - ADVFC32_17 |
|
|
Link URL |
Chính sách bảo mật |
ALLDATASHEET.VN |
Cho đến nay ALLDATASHEET có giúp ích cho doanh nghiệp của bạn hay không? [ DONATE ] |
Alldatasheet là | Quảng cáo | Liên lạc với chúng tôi | Chính sách bảo mật | Trao đổi link | Tìm kiếm theo nhà sản xuất All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |