Thermocouple and RTD Modules for Compact FieldPoint
cFP-RTD-124
The cFP-RTD-124 includes eight inputs for 2- and 4-wire RTDs. The module
uses a stable current source for sensor excitation and an onboard
microcontroller that linearizes and scales the measurements to temperature
units. You can configure each channel of the modules to return data scaled
to temperature (°C, °F, or °K) or resistance. Four-wire RTDs used with the
cFP-RTD-124 are ideal for applications involving long signal wires or high
signal noise. The 4-wire configuration eliminates the voltage drop caused
by lead wire resistance and reduces errors caused by noise.
Smart I/O Modules
The cFP-TC-12x and cFP-RTD-12x modules offer 16-bit resolution for
high-accuracy measurements, and you can connect directly to industrial
sensors or units under test with the safety isolation available. The
modules filter, calibrate, and scale raw sensor signals to engineering
units, as well as perform self-diagnostics to look for problems such as
open thermocouples. With cFP-TC-12x and cFP-RTD-12x modules, your
software application reads a linearized, calibrated, scaled value from the
I/O module, eliminating the error-prone step of converting binary values
to temperature. For increased accuracy and noise rejection, the modules
use a16-bit delta-sigma analog-to-digital converter (ADC) with an
integrated notch filter on each channel, which is configured for 50 and
60 Hz rejection. With high-accuracy 16-bit delta-sigma ADCs on the I/O
modules, you also get instrument-quality measurements on an industrially
rugged, distributed, embedded system. The cFP-TC-12x and cFP-RTD-12x
modules offer a variety of update rates to fit your application, ranging
from 0.22 s with filters off and 1.08 to 1.13 s with filters enabled. Overall
data throughput depends on filter settings across all channels, software
loop speeds, and network speeds.
Isothermal Connectivity for cFP-TC-12x Modules
For maximum accuracy, NI recommends using an isothermal connector
block with a cFP-TC-12x. The cFP-CB-3 isothermal connector block
minimizes the temperature gradient across wiring connections,
improving the accuracy of the cold-junction measurement, and,
therefore, of thermocouple measurements.
Compact FieldPoint I/O Connections
Compact FieldPoint modules include a built-in power distribution bus
that provides multiple power connections on the module. A field-wired
power supply connected to the voltage (V) and common (C) terminals is
internally connected to a power distribution bus that features additional
breakout terminals for voltage supply (VSUP) and common (COM). These
terminals offer a convenient way to distribute power to field devices that
require external power.
Each cFP-TC-12x input channel has two terminals for differential input:
1. Thermocouple positive input (IN+)
2. Thermocouple negative input (IN-)
Each cFP-RTD-122 input channel has three terminals:
1. Excitation output (EXCITE)
2. Sensing input (SENSE)
3. Common input (COM)
Each cFP-RTD-124 input channel has four terminals:
1. Excitation output (EXCITE)
2. Positive sensing input (SENSE+)
3. Negative sensing input (SENSE-)
4. Common input (COM)
cFP-TC-120
The cFP-TC-120 includes eight differential inputs for thermocouples.
It also provides cold-junction compensation using a thermistor embedded
in the connector block. An onboard microcontroller compensates and
linearizes the thermocouple reading to the NIST ITS-90 standard,
using an advanced linearization routine for maximum accuracy.
cFP-TC-125
In addition to the thermistor and linearization features of the cFP-TC-120,
the cFP-TC-125 provides 250 V
rms
of common-mode rejection, ideal for
applications where differences in voltages might exist between connected
thermocouples. The cFP-TC-125 also offers 0.22 s update rates when the
50/60 Hz filter is not enabled.
cFP-RTD-122
The cFP-RTD-122 includes eight inputs for 2- and 3-wire RTDs.
The module uses a stable current source for sensor excitation and an
onboard microcontroller that linearizes and scales the measurements to
temperature units. You can configure each channel of the module to
return data scaled to temperature (°C, °F, or °K) or resistance. The 3-wire
configuration used with the cFP-RTD-122 eliminates errors caused by
lead wire resistance but does not reduce errors caused by noise. If your
application involves high noise or long wires, you should use 4-wire RTDs
with the cFP-RTD-124.
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