Information

www.ti.com/automation
Electronic weigh scales, which are found in many
industrial applications, use a load cell as the
primary transducer. Load-cell designs can be
distinguished according to the type of output
signal they generate – pneumatic, hydraulic or
electric. Strain-gauge load cells convert the load
acting on them into electrical signals in the range
of millivolts per volt. A major challenge in
designing weigh scales is that they must sample
multiple load cells while producing extremely low
input referred noise.
Another important factor is the analog circuitry’s
long-term stability with regard to offset drift and
gain. Here the accuracy of the amplifi ed input
signal, either single-ended or differential, must
be guaranteed over years of operation. Hence
the signal chain has to handle the small signals
accurately in the presence of noise in addition
to conditioning for offset, drift, temperature
dependency and other factors.
TI’s ADS1232 is designed as a highly integrated
delta-sigma ADC for low-level, high-precision
measurements, especially for weigh-scale
applications. The device consists of a low-drift,
low-noise instrumentation amplifi er (selectable
gain) and a high-order, chopper-stabilized
modulator followed by a digital fi lter in a
monolithic device. This is a single-chip solution
that can be directly interfaced as a front end to a
load-cell bridge output.
Features and Benefi ts
• Complete front-end solution for weigh
scales
• Very low-noise PGA
• Only 17-nV input-referred noise with gain
of 128
• 23.5 effective bits with gain of 1
• Excellent 50-/60-Hz rejection:
100 dB (min)
Electronic Weigh Scale
Load Cell
Load Cell
Load Cell
Load Cell
LCD
Backlight
RS-232
RS-485
Ethernet
Filtering
ADC
AMP
Battery
Powered
Line
Powered
Power Management
O
R
AC
Adapter
AC Line
Plug
Integrated ADC
Solution
MCU
VREF
Wireless
The electromagnetic fl owmeter consists of a
nonferromagnetic tube wrapped with a magnetic
coil. Electrodes in the tube’s inner isolated surface
are in contact with a conductive liquid that fl ows
through the tube. The coils around the pipe
generate a magnetic fi eld within the tube. The
magnetic fi eld inducts a voltage in the liquid that
is proportional to the speed of the liquid in the
tube. This voltage is measured via the electrodes.
Because the measured voltage is very low, precise
low-noise signal conditioning is required.
Coriolis fl owmeter is a popular fl owmeter
that directly measures mass fl ow rate. Applying a
strong magnetic fi eld to a pipe through which fl uid
is fl owing makes the pipe oscillate at a particular
resonant frequency. When the fl uid starts fl owing
through the pipe, it is subject to Coriolis force.
The oscillatory motion of the pipe superimposes
on the linear motion of the fl uid, exerting twisting
forces on the pipe. This twisting is due to Coriolis
acceleration acting in opposite directions on either
side of the pipe and to the fl uid’s resistance to
the vertical motion. Sensor electrodes placed on
both the inlet and outlet sides pick up the phase
difference caused by this motion. This phase shift
due to the twisting forces is a direct measurement
of mass fl ow rate.
Low-noise instrumentation amplifi ers followed
by precision ADCs is typical of the signal-chain
path. Precision DACs or PWM drivers are used to
excite the fi eld coils. Multiple-channel ADCs with
simultaneous sampling architectures make it
possible to take multiple measurements such as
temperature, phase, density, etc. at the same time.
TI’s ADS1274, which is a 24-bit, 4-channel,
simultaneous-sampling delta-sigma converter
with up to 144 kSPS, is the perfect front end for
fl owmeters requiring multiple measurements
(Coriolis). The ADS1259 is a high-linearity, low-
drift, 24-bit, delta-sigma converter commonly used
in electromagnetic fl owmeters.
Features and Benefi ts
• Multiple channels and simultaneous
sampling for measuring multiple process
variables at the same time
• Excellent AC and DC performance
• Selectable operating modes: High speed,
high resolution, low power
Flowmeters: Electromagnetic/Coriolis
IO-Link
Processor
Processor
Power Management
ADC
ADC
ADC
Driver
The Magnetic-Inductive Flowmeter
Driver
The Coriolis Flowmeter
Isolation
PROFIBUS
RS-232/RS-485
Wireless
4-20mA
DAC
HART
Isolation
Line
Powered
Loop
Powered
O
R
IO-Link
PROFIBUS
RS-232/RS-485
Wireless
4-20mA
DAC
HART
Flow
Flow