Question

Choose the most correct answer

1. The LVDT is connected with deflection bridge for displacement and pressure measurement
   1. True
   2. False

2. In real work life, the accelerometer signal is integrated twice to obtain the displacement
   1. True
   2. False

3. The vortex flow meter measures the flow rate based on ultrasonic sensor
   1. True
   2. False

4. A force measurement system with range 0-1000 N, linearity error=0.1% FSO,

Hysteresis error=0.1% FSO, repeatability error=0.15% FSO, and zero drift=0.2% FSO, then the overall instrument error is

1. 5.1%
2. 0.63%
3. 0.29%

Answer 1

• (() False

LVDT is a normal type of transducer. The main function of this is to convert the rectangular movement of an object to the equivalent electrical signal. LVDT is used to calculate displacement and works on the transformer principle.

An LVDT measures displacement by associating a specific signal value for any given position of the core. This association of a signal value to a position occurs through electromagnetic coupling of an AC excitation signal on the primary winding to the core and back to the secondary windings. The position of the core determines how tightly the signal of the primary coil is coupled to each of the secondary coils. The two secondary coils are series-opposed, which means wound in series but in opposite directions. This results in the two signals on each secondary being 180 deg out of phase. Therefore phase of the output signal determines direction and its amplitude, distance.

An LVDT is incorporated into a pressure measurement device by connecting the core of the LVDT to the centre of a pressure sensing diaphragm, so that any flexing of the diaphragm due to changes in pressure will be detected as a position change by the LVDT.

• (a) True,

In reality, accelerometers have long been used to measure displacement. The acceleration signal coming from the sensing crystal is first conditioned, that is, made readable by subsequent measurement amplifiers. Once amplified to an acceptable level, the signal is passed through a double integrator, which is similar in design to a low pass filter. This AC signal, representative of the machine displacement, is fed into the averaging circuit, converted to the required DC value, and passed out of the sensor as a 4-20 mA signal. Now, data screens for process control machinery can be calibrated in mils displacement in the same manner that vibration velocity signals have been recorded with previous generation sensors.

• (a) True,

Since the time of ultrasonic wave propagation varies in proportion to the frequency generated by the vortexes, it follows that the flowrate can be measured by detecting changes in the time of ultrasonic wave propagation.
The ultrasonic sensors, being installed outside the conduit of the flowmeter body, allow users to perform
measurement tasks without having to touch the fluid under test. The sensing flowmeter offers greater
vibration immunity, offering a host of features, including high sensitivity.

• Option (c) = 0.29 %

An estimate of the overall instrument error is made by combining the estimates of all known errors into a term called the instrument uncertainty. The estimate is computed from the square root of the sum of
the squares of all known uncertainty values,