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參數(shù)資料
| 型號： | LMV844 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | CMOS Input, RRIO, Wide Supply Range Operational Amplifiers |
| 中文描述： | CMOS輸入，RRIO，寬電源電壓范圍運算放大器 |
| 文件頁數(shù)： | 15/18頁 |
| 文件大?。?/td> | 419K |
| 代理商： | LMV844 |
20168370
FIGURE 7. K-Type Thermocouple Response
Thermocouple Example
Suppose the range we are interested in for this example is
from 0°C to 500°C, and the resolution needed is 0.5°C. The
power supply for both the LMV841 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 shown in
Figure 7
To obtain the best accuracy the full ADC range of 0 to 3.3V is
used.
We can calculate the gain we need for the full input range of
the ADC : A
V
= 3.3V / 0.0206V = 160.
When we use 2 k
for R
, we can calculate the value for R
F
with this gain of 160. We can use A
= R
F
/ R
G
to calculate
the gain, so we can calculate R
F
by using R
F
= A
V
x R
G
= 160
x 2 k
= 320 k
.
To get a resolution of 0.5°C we need a step smaller then the
minimum resolution, this means we need at least 1000 steps
(500°C / 0.5°C). A 10-bit ADC would be sufficient as this will
give us 1024 steps. This could be a 10 bit ADC like the two
channel 10-bit ADC102S021.
Unwanted Thermocouple Effect
At the point where the thermocouple wires are connected to
the circuit, usually copper wires or traces, an unwanted ther-
mocouple effect will occur.
At this connection, this could be the connector on a PCB, the
thermocouple wiring forms a second thermocouple with the
connector. This second thermocouple disturbs the measure-
ments from the intended thermocouple.
We can compensate for this thermocouple effect by using an
isothermal block as a reference. An isothermal block is a good
heat conductor. This means that the two thermocouple con-
nections both have the same temperature. We can now mea-
sure the temperature of the isothermal block, and thereby the
temperature of the thermocouple connections. This is usually
called the cold junction reference temperature.
In the example, an LM35 is used to measure this temperature.
This semiconductor temperature sensor can accurately mea-
sure temperatures from 55°C to 150°C.
The ADC in this example also coverts the signal from the
LM35 to a digital signal. Now the microprocessor can com-
pensate the amplified thermocouple signal, for the unwanted
thermocouple effect.
20168353
FIGURE 8. Thermocouple Amplifier
15
www.national.com
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LMV844MA | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:CMOS Input, RRIO, Wide Supply Range Operational Amplifiers |
| LMV844MA/NOPB | 功能描述:運算放大器 - 運放 12V CMOS RRIO Amp 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(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMV844MAX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:CMOS Input, RRIO, Wide Supply Range Operational Amplifiers |
| LMV844MAX/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(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMV844MT | 制造商:Texas Instruments 功能描述:OP Amp Quad GP R-R I/O 12V 14-Pin TSSOP Rail 制造商:Texas Instruments 功能描述:IC, OP AMP, RRIO, 12V, TSSOP14, 844 |
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