Campbell AVW1, Instruction Manual

Page: 16 / 36

AVW1/AVW4
3-4
Example: Using sensor number 3998 and
assuming a sensor temperature of 15
o
C, the
corrected pressure would be:
Pt = P psi + (-0.0698 psi/
o
C)*(15
o
C - 24
o
C)
= P psi + 0.6282 psi
3.6 DELAY BETWEEN
MEASUREMENTS
The vibrating wire sensor should not be excited
more often than once every five time constants
if high resolution is important. If more than one
repetition is specified the "delay before
excitation applied" parameter can be used to
ensure the proper amount of delay between
excitations. Excitation of the sensor while the
wire is still vibrating can cause the signals to
add or subtract (in phase or out of phase)
causing the wire to vibrate excessively hard or
almost not at all.
If two back to back measurements are required
they can be done one of two ways. With the
AVW4 the repetitions parameter must be set to
2--. The "--" instructs the CR10 to excite both
sensors, delay 20 ms, measure the first sensor,
and then measure the second sensor. There is
no delay or re-application of the excitation
between the measurements. Back to back
measurements require that the sum of the
number of cycles measured on each sensor not
exceed the time constant of the last sensor or
the signal may have become too week to be
measured. (e.g., two sensors measured
separately, each having a time constant equal
to 700 cycles would have to be measured back
to back with a maximum of 350 cycles.) Back
to back measurements with two AVW1s and
two excitation channels can be done simply by
entering Instruction 28 twice, once for the first
sensor and once for the second. In this case
the second AVW1 measurement will begin 170
milliseconds after the first one ended.