LTC2414IGN datasheet(36/48 Pages) LINER

36 / 48 page

LTC2414/LTC2418

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

CH0

CH1

GND

VCC

350

Ω

BRIDGE

2414/18 F41

LTC2414/

LTC2418

R1 AND R2 CAN BE USED TO INCREASE TOLERABLE AC COMPONENT ON REF SIGNALS

LT1019

0.1

µF

0.1

µF

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

LTC2414IGN Datasheet(PDF) 36 Page - Linear Technology

LTC2414IGN Datasheet(HTML) 36 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Datasheet Download

Link URL