Appendix D. Engineering output
and calibration
The
basic
measurement
outputs
given
by
the
CRVW3
are
sensor
frequency
and,
if
a
thermistor
is
used,
sensor
temperature.
These
values
can
be
used
both
to
calculate
an
output
value
in
engineering
units,
as
well
as
to
form
the
basis
for
calibration
adjustments
that
are
stored
and
applied
to
the
outputs.
D.1
Engineering
output
The
frequency
reading
on
the
CRVW3
is
expressed
both
in
units
of
Hertz
(Hz)
and
in
units
of
digits
(Hz
2
/1000).
The
CRVW3
can
be
configured
to
calculate
an
output
value
that
is
specified
in
engineering
units
of
measure
or
dimensions.
Examples
of
units
are
kPa,
millibar,
mmHg,
mmH
2
0,
in.,
ft,
or
m
for
piezometers,
µε
(microstrain)
or
ε
(strain)
for
strain
ga
u
ges,
kg,
ton,
or
lb
for
load
cells,
and
mm
or
in.
for
crackmeters.
The
CRVW3
implements
a
polynomial
that
works
with
most
vibrating-wire
sensors,
and
it
uses
frequency
and
temperature
as
inputs.
NOTE:
Some sensor calibration sheets report data in units of digits or B units. The relationship
between Hertz and digits or B units is shown in the following formula:
digits or B units = Hz
2
/ 1000
The sensor manual should include information that describes the process of converting a
frequency and temperature value pair into engineering output. Sometimes the temperature
value is not used. Constants involved in the calculation are often slightly different for each
manufactured sensor, in which case a calibration sheet or calibration record will be provided with
each individual sensor. This information will be necessary in configuring the settings of the
CRVW3 to obtain the desired result. Determine most of the details for calculating engineering
output by using typical sensors in the lab or office before field deployment.
The settings used on the CRVW3 to configure engineering output are found in
Device
Configuration Utility
> Settings Editor > Channel 1, Channel 2, and Channel 3. See
(p. 21) for more information.
A temperature reading cannot be used as part of the calculation unless it is expressed in units of
degrees Celsius; raw resistance in ohms will not work. To use temperature as part of the output
CRVW3 3-Channel Vibrating-Wire Data Logger
81
