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參數(shù)資料
| 型號： | LMV854MT |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 運動控制電子 |
| 英文描述： | 8 MHz Low Power CMOS, EMI Hardened Operational Amplifiers |
| 中文描述： | OP-AMP, 1200 uV OFFSET-MAX, 8 MHz BAND WIDTH, PDSO14 |
| 封裝： | TSSOP-14 |
| 文件頁數(shù)： | 17/22頁 |
| 文件大?。?/td> | 994K |
| 代理商： | LMV854MT |
20202160
FIGURE 7. Pressure Sensor Application
THERMOCOUPLE AMPLIFIER
The following circuit is a typical example for a thermocouple
amplifier application using an LMV851/LMV852, or LMV854.
A thermocouple converts a temperature into a voltage. This
signal is then amplified by the LMV851/LMV852, or LMV854.
An ADC can convert the amplified signal to a digital signal.
For further processing the digital signal can be processed by
a microprocessor and used to display or log the temperature.
The temperature data can for instance be used in a fabrication
process.
Characteristics of a Thermocouple
A thermocouple is a junction of two different metals. These
metals produce a small voltage that increases with tempera-
ture.
The thermocouple used in this application is a K-type ther-
mocouple. A K-type thermocouple is a junction between Nick-
el-Chromium and Nickel-Aluminum. This is one of the most
commonly used thermocouples. There are several reasons
for using the K-type thermocouple, these include: tempera-
ture range, the linearity, the sensitivity, and the cost.
A K-type thermocouple has a wide temperature range. The
range of this thermocouple is from approximately 200°C to
approximately 1200°C, as can be seen in
Figure 8
. This cov-
ers the generally used temperature ranges.
Over the main part of the temperature range the output volt-
age depends linearly on the temperature. This is important for
easily converting the measured signal levels to a temperature
reading.
The K-type thermocouple has good sensitivity when com-
pared to many other types; the sensitivity is about 41 uV/°C.
Lower sensitivity requires more gain and makes the applica-
tion more sensitive to noise.
In addition, a K-type thermocouple is not expensive, many
other thermocouples consist of more expensive materials or
are more difficult to produce.
20202162
FIGURE 8. K-Type Thermocouple Response
Thermocouple Example
For this example, suppose the range of interest is 0°C to
500°C, and the resolution needed is 0.5°C. The power supply
for both the LMV851/LMV852, or LMV854 and the ADC is
3.3V.
The temperature range of 0°C to 500°C results in a voltage
range from 0 mV to 20.6 mV produced by the thermocouple.
This is indicated in
Figure 8
by the dotted lines.
To obtain the highest resolution, the full ADC range of 0 to
3.3V is used. The gain needed for the full range can be cal-
culated as follows:
A
V
= 3.3V / 0.0206V = 160
If R
is 2 k
, then the value for R
can be calculated for a gain
of 160. Since A
V
= R
F
/ R
G
, RF can be calculated as follows:
R
F
= A
V
x R
G
= 160 x 2 k
= 320 k
To get a resolution of 0.5°C, the LSB of the ADC should be
smaller then 0.5°C / 500°C = 1/1000. A 10-bit ADC would be
sufficient as this gives 1024 steps. A 10-bit ADC such as the
two channel 10-bit ADC102S021 can be used.
17
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LMV854MT/NOPB | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風格:SMD/SMT 封裝 / 箱體:QFN-16 轉換速度:0.89 V/us 關閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMV854MTX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:8 MHz Low Power CMOS, EMI Hardened Operational Amplifiers |
| LMV854MTX/NOPB | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風格:SMD/SMT 封裝 / 箱體:QFN-16 轉換速度:0.89 V/us 關閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMV861 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:30 MHz Low Power CMOS, EMI Hardened Operational Amplifiers |
| LMV861MG | 制造商:Texas Instruments 功能描述:OP Amp Single GP R-R O/P 5.5V 5-Pin SC-70 T/R 制造商:Rochester Electronics LLC 功能描述: |
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