参数资料
型号: DC571A
厂商: Linear Technology
文件页数: 30/48页
文件大小: 0K
描述: BOARD DELTA SIGMA ADC LTC2418
软件下载: QuikEval System
设计资源: DC571A Design File
DC571A Schematic
标准包装: 1
系列: QuikEval™
ADC 的数量: 1
位数: 24
采样率(每秒): 7.5
数据接口: MICROWIRE?,串行,SPI?
工作温度: 0°C ~ 70°C
已用 IC / 零件: LTC2418
已供物品:
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LTC2414/LTC2418
36
241418fa
BRIDGE APPLICATIONS
Typical strain gauge based bridges deliver only 2mV/Volt
of excitation. As the maximum reference voltage of the
LTC2414/LTC2418 is 5V, remote sensing of applied exci-
tation without additional circuitry requires that excitation
be limited to 5V. This gives only 10mV full scale input
signal, which can be resolved to 1 part in 10000 without
averaging. For many solid state sensors, this is still better
than the sensor. Averaging 64 samples however reduces
the noise level by a factor of eight, bringing the resolving
power to 1 part in 80000, comparable to better weighing
systems. Hysteresis and creep effects in the load cells are
typically much greater than this. Most applications that
require strain measurements to this level of accuracy are
measuring slowly changing phenomena, hence the time
required to average a large number of readings is usually
not an issue. For those systems that require accurate
measurement of a small incremental change on a signifi-
cant tare weight, the lack of history effects in the LTC2400
family is of great benefit.
For those applications that cannot be fulfilled by the
LTC2414/LTC2418 alone, compensating for error in exter-
nal amplification can be done effectively due to the “no
latency” feature of the LTC2414/LTC2418. No latency
operation allows samples of the amplifier offset and gain
to be interleaved with weighing measurements. The use of
correlated double sampling allows suppression of 1/f
noise, offset and thermocouple effects within the bridge.
Correlated double sampling involves alternating the polar-
ity of excitation and dealing with the reversal of input
polarity mathematically. Alternatively, bridge excitation
can be increased to as much as
±10V, if one of several
precision attenuation techniques is used to produce a
precision divide operation on the reference signal. An-
other option is the use of a reference within the 5V input
range of the LTC2414/LTC2418 and developing excitation
via fixed gain, or LTC1043 based voltage multiplication,
along with remote feedback in the excitation amplifiers, as
shown in Figures 46 and 47.
Figure 41 shows an example of a simple bridge connec-
tion. Note that it is suitable for any bridge application
where measurement speed is not of the utmost impor-
tance. For many applications where large vessels are
weighed, the average weight over an extended period of
time is of concern and short term weight is not readily
determined due to movement of contents, or mechanical
resonance. Often, large weighing applications involve load
cells located at each load bearing point, the output of
which can be summed passively prior to the signal pro-
cessing circuitry, actively with amplification prior to the
ADC, or can be digitized via multiple ADC channels and
summed mathematically. The mathematical summation
of the output of multiple LTC2414/LTC2418’s provides the
benefit of a root square reduction in noise. The low power
consumption of the LTC2414/LTC2418 makes it attractive
for multidrop communication schemes where the ADC is
located within the load-cell housing.
REF+
REF
SDI
SCK
SDO
CS
20
18
17
16
CH0
CH1
GND
VCC
FO
11
R1
12
350
BRIDGE
21
22
2414/18 F41
15
9
19
LTC2414/
LTC2418
+
R2
R1 AND R2 CAN BE USED TO INCREASE TOLERABLE AC COMPONENT ON REF SIGNALS
LT1019
0.1
F
0.1
F
10
F
Figure 41. Simple Bridge Connection
A direct connection to a load cell is perhaps best incorpo-
rated into the load-cell body, as minimizing the distance to
the sensor largely eliminates the need for protection
devices, RFI suppression and wiring. The LTC2414/
LTC2418 exhibits extremely low temperature dependent
drift. As a result, exposure to external ambient tempera-
ture ranges does not compromise performance. The in-
corporation of any amplification considerably compli-
cates thermal stability, as input offset voltages and cur-
rents, temperature coefficient of gain settling resistors all
become factors.
APPLICATIO S I FOR ATIO
WU
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