6.0 POWERING
All ICP® sensors require constant current excitation
for proper operation. For this reason only use
approved constant-current sources. A typical system
schematic is shown in Figure 11.
The power supply consists of a regulated 18 to 30
VDC source. In general, battery-powered devices
offer
versatility
for
portable,
low-noise
measurements, whereas line-powered units provide
the capability for continuous monitoring. This power
is regulated by a current-limiting circuit, which
provides the constant-current excitation required for
proper operation of sensors with integral
electronics.
Note:
Under no circumstances should a voltage be
supplied to an ICP® accelerometer without a current-
regulating diode or equivalent electrical circuit.
A capacitor at the output stage of the device
removes the sensor output bias voltage from the
measurement signal. This provides a zero-based, AC-
coupled output compatible with most standard
readout devices.
Today, many FFT analyzers, data acquisition
modules, and data collectors have constant-current
excitation for direct use with ICP® sensors. However,
before using this feature, check that the supply
voltage and constant current are adequate for use
with your sensor. Please contact the respective
signal conditioner manufacturer or check the
product manual for more information.
7.0 OPERATING
After completing the system setup, switch on the
conditioner, the meter (or LED) and allow the sensor
to power up. If a faulty condition is monitored, first
check all system connections, then check the
functionality of the cable and signal conditioner. If
the system still does not operate properly, consult
an IMI Application Engineer.
Note:
Always operate the accelerometer within the
limitations listed on the Specification Sheet of your
sensor. Operating the device outside of its
parameters can cause temporary or permanent
damage to the sensor.
8.0 ACCELEROMETER CALIBRATION
Note:
It is good measurement practice to verify the
performance of each accelerometer before and after
each measurement.
Accelerometers
are
precision
measuring
instruments. They are highly engineered to provide
accurate electrical signals representative of the
vibration being monitored. Each sensor is calibrated
by comparison to a known acceleration level. Some
calibrations include frequency response curves,
resonant
frequency
measurements,
transvers
sensitivity, and many other valuable tests.
Applications requiring a high degree of accuracy or
those in plants requiring certification and traceability
require full calibration test results.
Some applications have much less stringent
requirements for calibration certification. Simple
sensitivity measurements at a single frequency may
be sufficient; operational verification and certificates
of conformance to published specifications may
satisfy many plants’ calibration needs. Reducing the
final calibration requirements reduces the cost of
manufacturing the sensor and should lower the price
for predictive maintenance users.
