Essential Concepts in Measurement and Instrumentation Systems
Draw and explain working of ramp type ADC with block diagram and waveform.
Working Principle:
Start
Signal
A start signal initializes the ramp generator and resets the counter.
Ramp
Generation
The ramp generator starts generating the sawtooth waveform.
Comparison
The comparator continuously compares the ramp voltage with the analog input voltage.
Counting
As long as the ramp voltage is lower than the analog input, clock pulses are allowed to pass through the gate circuit and are counted by the counter.
Stop Signal
When the ramp voltage equals or exceeds the analog input voltage, the comparator triggers a stop signal, disabling the gate and halting the counter.
Digital Output
The number of clock pulses counted by the counter at the point of stop is the digital representation of the analog input voltage.
Draw and explain magnetic tape recording process.
Recording process
Signal Conversion:
An electrical signal (representing audio or video) is fed into the recording head.
2. Magnetic Field:
The recording head, which is essentially an electromagnet, creates a magnetic field that varies according to the input signal.
3. Tape Movement:
The magnetic tape is drawn past the recording head at a constant speed.
4. Magnetic Imprint:
As the tape passes, the varying magnetic field from the head aligns the tiny magnetic particles in the tape’s coating, creating a magnetic pattern that represents the original signal.
Explain displacement measurement using LVDT with phase-sensitive demodulation.
Working of LVDT (Linear Variable Differential Transformer):
1. Construction
Contains one primary coil (P) and two secondary coils (S1 and S2) placed on either side of the primary.
A movable soft iron core is placed inside the coils.
2. Operation
An AC voltage is applied to the primary coil.
The core movement causes differential voltages in S1 and S2.
If core is centered, voltages in S1 and S2 cancel ⇒ output = 0.
If core moves towards S1, Vₒ becomes positive.
If core moves towards S2, Vₒ becomes negative.
✅ Role of Phase Sensitive Demodulator (PSD)
The LVDT output is an AC signal whose amplitude and phase depend on the core position.
The PSD converts this AC signal into a DC voltage:
Magnitude ∝ amount of displacement.
Polarity indicates direction (positive or negative displacement).
This gives a linear, noise-free, and direction-sensitive output.
✅ Applications
Accurate linear displacement measurement in automation, robotics, and control systems.
Draw and explain the block diagram of a generalized instrumentation system.Describe each block in brief.
Primary sensing element
The primary sensing element is also known as sensor. Basically transducers are used as a primary sensing element. Here, the physical quantity (such as temperature, pressure etc.) are sensed and then converted into analogues signal.
Variable conversion element
It converts the output of primary sensing element into suitable form without changing information. Basically these are secondary transducers.
Variable manipulation element
The output of transducer may be electrical signal i.E. Voltage, current or other electrical parameter. Here, manipulation means change in numerical value of signal. This element is used to convert the signal into suitable range.
Data transmission element
Sometimes it is not possible to give direct read out of the quality at a particular place (Example – Measurement of temperature in the furnace). In such a case, the data should transfer from one place to another place through channel which is known as data transmission element.
Data presentation or controlling element
Finally the output is recorded or given to the controller to perform action. It performs different functions like indicating, recording or controlling.