Information

Temperature sensors are used to measure temp-
erature and have a wide range of uses in industrial
and com mer cial applications. Temperature
measure ments are commonly made by using a
resistance temperature detector (RTD), thermistor
or thermocouple.
RTDs have wire winding or thin-fi lm serpentine
elements that exhibit changes in resistance with
changes in temperature. Thermistors, typically
made of ceramic or polymer material, also exhibit
signifi cant changes in resistance with changes
in temperature. Thermocouples consist of two
dissimilar metal wires welded together to form
two junctions. Temperature differences between
the junctions cause a thermoelectric potential (i.e.,
a voltage) between the two wires. Holding the
reference junction at a known temperature and
measuring this voltage permits the temperature
of the sensing junction to be deduced. A constant
and linear excitation source is a critical aspect
of RTD/thermistor sensing, while cold junction
compensation is the key to a good temperature
measurement with thermocouples.
With its high integration, excellent resolution
and accuracy, the ADS1248 offers a single-chip
solution to all of these types of temperature
measurements. The ADS1118 is a lower-cost
solution which has the basic core needed for
any temperature measurement and an extremely
accurate on-chip temperature sensor that is
perfect for accurate cold junction compensation.
www.ti.com/automation
Pressure sensors convert a physical value –
weight, tire pressure, level, force or fl ow – into a
differential signal in the range of millivolts per volt
and use metal thick-fi lm, ceramic thin-fi lm, or
piezoresistive technologies, to name a few. The
majority of designers use the cost-effective
piezosensors that can sense 25 mbar to 25 bar.
However, these sensors are very nonlinear and
temperature-dependent and have a large offset
and large offset drift. They also require attention
to electronic calibration and compensation.
TI’s PGA309 sensor conditioner is an ideal
choice in combination with low-cost piezoresistive
or ceramic thin-fi lm pressure sensors. It is a
complete signal conditioner for bridge sensors
with versatile features that enable linearization,
temperature compensation and digital calibration.
Features and Benefi ts
• Bridge excitation and sensor signal
conditioning
• Sensor error compensation: span, offset
and temperature drifts
• Sensor linearization circuitry
• Digital calibration via one- or two-wire
serial interface
• Low, time-stable total adjusted error
Field Transmitter: Pressure Sensor
Keypad
On/Off
LCD
Display
ADC
Integrated Solution
MCU
4-20mA
4-20
DAC
Power Management
Battery
Powered
Line
Powered
Loop
Powered
O
R
O
R
Battery
Current
Source
MUX
egrated So
AMP
Isolation
Wireless
Antenna
RS-232/RS-485
PROFIBUS
IO-Link
LCD
Backlight
Filtering
-
+
Thermocouple
V
Filtering
RTD
or
Thermistor
V/I
HART
Field Transmitter: Temperature Sensor
Features and Benefi ts
• Highly integrated solution
– Dual matched-current DACs
– Low-drift internal reference
– Low-noise PGA, temperature sensor,
burnout detection
• 24 bits, no missing codes, single-cycle
settling, up to 2 kSPS
• 50-/60-Hz rejection
+125ºC
+40ºC
T
Nonlinear
Bridge
Transducer
Pressure
Power Management
Battery
Powered
Line
Powered
Loop
Powered
O
R
O
R
Battery
Wireless
Antenna
Integrated Solution
Linearization
Circuit
VREF
DAC
MUX
AMP
ADC
TMP
ADC
Cum Cubic Feet
MCU
4-20mA
RS-232/RS-485
PROFIBUS
IO-Link
DAC
HART
Isolation