|
Sensor element
|
VW
Sensors
|
FSG (Foil strain gage type) Sensors
|
|
Output
|
Frequency signal (㎐, μsec)
|
DC Voltage
|
|
Accuracy
|
Very accurate
|
Accurate
|
|
Applied gage factor : 0.5 ∼ 1.0 % FSR
Applied ABC factor : 0.1 ∼ 0.5 % FSR
|
Applied gage factor : 0.2 % ∼ 2.0 % FSR
|
|
Measuring
environments
|
Optimum in static measurement, VW sensors ate
incompetent in dynamic measurement.
|
Optimum in static measurement, Electrical resistance
sensors are rather competent in dynamic measurement
|
|
Be measured or not with
VW readout units manufactured by other company
|
VW sensors may be measured with any VW readout units, but
sometimes they may be not measured according to performance of them
|
Electrical resistance sensors may be not measured
according to input and output voltage, makers.
|
|
Thermal
zero shift
|
They are affected by coefficient of linear expansion
of materials. Thus they need to measure frequency and temperature signal and
to compensate temperature variations
|
Electrical resistance sensors that foil strain gages
are bonded to the body, compensate automatically for temperature variations.
On the contrary, electrical resistance sensors that are equipped with
potentiometers or electrolytic level sensors, need to compensate for
temperature variations.
|
|
Transmittable length
|
Usually 2 to 3 kilometers
|
Usually 200 to 300
meters
|
|
The frequency signal
means alternating current. Thus VW sensors are affected by cable resistance
and length. They can be transmitted to maximum 4 kilometers in shielded cable
|
The output from the
electrical resistance sensors is direct current. Voltage drop in cable
increases as its length become long
|
|
Effect of noise and
electromagnetic waves
|
Little influence
|
Great influence
|
|
When sources of vibration or impact supplied on the
transducer that the vibrating wire is fixed on one point, the instrument is
affected by them. In installation of those instrument. It needs to protect
the transducer from damage.
|
DC output from electrical resistance sensors is
feeble, so its magnitude may be altered by noise or electromagnetic waves. To
prevent these troubles, signal cables must be shielded on ground and be far
away from power cables and sources of electromagnetic waves. In addition,
signal cables must be installed perpendicular with power cables, if that
installation is inevitable. If troubles are not eliminated by means of
previous descriptions, the outer surface of signal cables must be covered
with tapes made by copper and then it must be grounded
|
|
Effect of vibrations and
impacts
|
Comparatively little
|
Very little
|
|
Permanent monitoring
|
Semi-permanent
|
A little restriction
|
|
VW sensors that are assembled with a music wire of high
elasticity of modulus are affected by secular change and fatigue, but effect
of creep is within error. Thus they can be monitored semi-permanently.
Permanent monitoring depends on design, manufacturing
skill and productive facilities for VW sensors
|
Foil strain gages bonded to the body with an adhesive
agent may come off. Permanent monitoring depends on design, skill bonding
gages and field environments for electrical resistance sensors
|
|
(Note) This table is just the general character to help
choosing a measurement device owing for a condition of a site and output
device that we have, So it can't be an absolute yardstick.
|
