Strain Gage Module for Compact FieldPoint
Overview
The National Instruments cFP-SG-140 is a versatile resistance bridge input
module for Compact FieldPoint that you can use to measure values from
resistor bridges including full- and half-bridge strain gages, quarter-bridge
strain gages (using an external completion register), and load and torque
sensors. The NI cFP-SG-140 includes built-in excitation, overranging, and
onboard diagnostics to ensure trouble-free installation and maintenance.
The module measures and linearizes signals on board to return scaled
values to your control or monitoring software. The cFP-SG-140 comes with
a NIST-traceable calibration certificate, ensuring accurate and reliable
analog measur
ements.
Strain Gage
With the cFP-SG-140, you can connect directly to industrial sensors or units
under test and get high-accuracy measurements. The module filters,
calibrates, and scales raw sensor signals to engineering units, as well as
perfor
ms self-diagnostics to look for problems with the module or wiring.
With the cFP-SG-140 module, your software application reads a linearized,
calibrated, and scaled value from the I/O module, eliminating the error-
pr
one step of conver
ting binar
y values.
Because the cFP-SG-140 measures in units of millivolts per volt, it
can interface with a wide variety of transducers, such as load cells and
pressure sensors. The module uses a pulsed excitation of up to 21 mA per
channel that turns on and off the excitation to each channel. This reduces
self-heating effects and pr
ovides mor
e accurate and repeatable strain
measurements. The cFP-SG-140 also of
fers tr
ue ratiometric
readings to
eliminate errors caused by variations in excitation voltage. You can
configure each channel on the module for a different excitation level of 2.5,
5, or 10 V. For increased accuracy and noise rejection, the cFP-SG-140 uses
a 16-bit delta-sigma ADC with an integrated lowpass filter on each channel,
which you can configure for 15, 60, or 240 Hz. With a high-accuracy 16-bit
delta-sigma ADC, you also get instrument-quality measurements on an
industrially rugged, distributed, embedded system.
The cFP-SG-140 has three update rates to fit your application, ranging from
0.87 to 1.11 Hz. These rates vary based on the noise filter setting selected on
the module. Overall data throughput depends on software loop speeds and
network speeds. W
ith over
ranging and under
ranging, the modules can zer
o
out unstrained readings in software to compensate for field devices with span
errors of up to 12 percent.
Isolation
The cFP-SG-140 features optical bank isolation with 2,300 V
r
ms
of
breakdown isolation. These Compact FieldPoint modules do not have
channel-to-channel isolation.
Field 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 offers additional breakout
terminals for voltage supply (V
SUP
) and common (COM). These terminals
deliver a convenient way to distribute power to field devices that require
external power.
• Accepts full- and half-bridge strain gage
inputs directly
• Quarter-bridge gages require external
bridge-completion resistor
• Compatible with load cells, force
sensors, and torque sensors
• Built-in signal conditioning
• 15, 60, and 240 Hz noise rejection
• Pulsed excitation to prevent
self-heating
• 16-bit resolution
• Input ranges software-configurable
per channel
•
2,300 V
r
ms
b
ank isolation for transient
overvoltage protection
• Hot-swappable with autoconfiguration
• -40 to 70 °C operating range
NI cFP-SG-140
M
odule
I
nput Channels
R
esolution
Input Ranges
(
Software-Configurable per Channel)
15/60/240 Hz
N
oise Filter
All Channel
U
pdate Rate
1
c
FP-SG-140
8 1
6 bits
±
3.5 mV/V, ±7.5 mV/V, ±30 mV/V, ±60 mV/V
S
oftware selectable
1
.11 to 0.87 Hz (rate varies with filter settings)
1
The all-channel update rate refers to the time the module takes to sample all channels. The overall system update rate is affected by other factors, such as the aggregate module update rate and
software loop rate. To calculate the system update rate, visit
ni.com/info and enter “systemrate.”
(33 paginas)
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