An LVDT has the following data : input = 6.3 V, Output = 5.2 V, range = ± 0.5 cm. The value of output voltage, when it is at 0.45 cm from the centre is given by
4.68 V
An LVDT is linear over its rated range, so the output is simply proportional to the displacement.
Step 1 — find the sensitivity. The quoted output of 5.2 V corresponds to the full-scale displacement of 0.5 cm:
\(S=\dfrac{5.2\ \text{V}}{0.5\ \text{cm}}=10.4\ \text{V/cm}\)
Step 2 — scale to the actual displacement.
\(V_{o}=S\times x=10.4\times0.45=4.68\ \text{V}\)
or equivalently \(V_{o}=5.2\times\dfrac{0.45}{0.5}=4.68\ \text{V}\) — option 1. The three distractors are the same figure divided by ten, a hundred and a thousand, so the only real risk is a units slip.
Note what the 6.3 V input is for. It is the primary excitation, and it does not enter this calculation, because the output figure of 5.2 V is already quoted for that excitation. It would matter only if the sensitivity were expressed per volt of excitation, as V/V/cm — here \(10.4/6.3=1.65\ \text{V/V/cm}\). Recognising which given quantity is redundant is part of the question.
How the device produces that linear output. A single primary is flanked by two identical secondaries wound in series opposition. With the ferromagnetic core centred, the two induced voltages are equal and cancel:
\(V_{o}=V_{s1}-V_{s2}=0\ \text{at the null}\)
Displacing the core increases the coupling to one secondary and decreases it to the other, so the difference grows linearly with displacement, and its phase reverses on passing through the null — which is how the direction of travel is recovered by phase-sensitive detection.
| Property | LVDT |
|---|---|
| Measures | Linear displacement |
| Null output | Ideally zero (a small residual in practice) |
| Friction | None — the core does not touch the coils |
| Resolution | Effectively infinite, limited by the electronics |
The frictionless, non-contacting construction is the LVDT's great advantage: nothing wears out, so it lasts indefinitely and offers extremely fine resolution — which is why it is standard in gauging, servo position feedback and load cells. Its rotary counterpart, for angular measurement, is the RVDT.
Hence, the output voltage is 4.68 V.
Similar Questions
An LVDT is used for measuring the deflection of bellows. The sensitivity of LVDT is 40V per mm. The bellows is deflected by 0.125 mm by a pressure of 0.8 x 106 N per m2. Determine the sensitivity of the LVDT in V per N/m2, when the voltage output of LVDT is 3.1 V.
Consider the following statements regarding the advantages of Anderson Bridge
A. It is the modification of the Maxwell's inductance Capacitance Bridge
B. For measuring the low Q of coils, it is not superior to Maxwell's bridge
C. It is not simple as compared to Maxwell's Bridge
D. It can be used to determine mutual inductance
Choose the correct answer from the options given below:
Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R
Assertion A : Potentiometric type accelerometer have higher resolution than LVDT accelerometer.
Reason R : The resistance offered to the motion is less in LVDT accelerometer than in potentiometric accelerometer.
In the light of the above statements, choose the most appropriate answer from the options given below :
An angular position to be measured using a transducer. Which of the following types of transducers can be used for this purpose ?
1. Circular potentiometer
2. LVDT
3. E-pick off
4. SynchroSelect the correct answer using the codes given below :
Codes :
Important Questions from Inductive Transducers - Teaching
An LVDT is used for measuring the deflection of bellows. The sensitivity of LVDT is 40V per mm. The bellows is deflected by 0.125 mm by a pressure of 0.8 x 106 N per m2. Determine the sensitivity of the LVDT in V per N/m2, when the voltage output of LVDT is 3.1 V.
Consider the following statements regarding the advantages of Anderson Bridge
A. It is the modification of the Maxwell's inductance Capacitance Bridge
B. For measuring the low Q of coils, it is not superior to Maxwell's bridge
C. It is not simple as compared to Maxwell's Bridge
D. It can be used to determine mutual inductance
Choose the correct answer from the options given below:
Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R
Assertion A : Potentiometric type accelerometer have higher resolution than LVDT accelerometer.
Reason R : The resistance offered to the motion is less in LVDT accelerometer than in potentiometric accelerometer.
In the light of the above statements, choose the most appropriate answer from the options given below :
An angular position to be measured using a transducer. Which of the following types of transducers can be used for this purpose ?
1. Circular potentiometer
2. LVDT
3. E-pick off
4. SynchroSelect the correct answer using the codes given below :
Codes :
