ICAR AIEEA-PG — Agricultural Engineering & Technology (Major Subject Group 10) · India · National Testing Agency for ICAR
Original practice questions written to the published syllabus · not past papersMeasuring temperature, pressure, flow, force and moisture, logging the data, and controlling processes automatically.
In the exams: ICAR AICE subjects 38 (Unit 7), 39 (Unit 8) and 41 (Unit 9); NCEES PE sensors and data acquisition; NCEES FE 4–6 questions
ICAR AIEEA-PG — Agricultural Engineering & Technology (Unit II)
Basic instruments and measurement: errors, sensitivity, transducer classification, temperature and pressure measurement, ADC resolution and simple amplifier circuits.
How our questions for ICAR AIEEA-PG spread across the units of Instrumentation, Sensors & Process Control. Difficulty: 36 easy, 4 medium, 0 hard.
| The generalised measurement system | 5 | |
| Static and dynamic characteristics of instruments | 4 | |
| Temperature transducers | 4 | |
| Pressure, flow and level measurement | 4 | |
| Moisture measurement | 4 | |
| Signal conditioning | 4 | |
| IoT sensor networks | 4 | |
| Data acquisition and data loggers | 3 | |
| Programmable logic controllers | 3 | |
| Control modes: on-off, P, PI and PID | 3 | |
| Force, torque and strain: strain gauges and load cells | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
In the generalised measurement system, which functional element changes the magnitude of a signal without changing its physical nature?
A. The variable-manipulation element, for example an amplifier raising a millivolt signal to volts
Variable manipulation changes size, not kind: an amplifier makes a small voltage into a larger voltage. Variable conversion changes the kind of signal (pressure to displacement), the primary element senses the measurand, and the presentation element shows or stores the result.
Which of these transducers is self-generating (active), producing an output without any external excitation supply?
C. A thermocouple, which produces an emf from the temperature difference between its junctions
A thermocouple generates its own emf by the Seebeck effect. RTDs, strain gauges and capacitive sensors are passive: their resistance or capacitance changes, and an excitation voltage or current is needed to turn that change into a signal.
A grain-probe temperature sensor has a time constant of 8 s. About how long after a step change does it show 95% of the change?
B. 24 s
A first-order response reaches 1 − e^(−3) = 95.0% at three time constants: 3 × 8 = 24 s. 8 s gives only 63.2%, 16 s (2τ) gives 86.5%, and 40 s (5τ) gives 99.3%.
What does the designation 'Pt100' on a resistance temperature detector mean?
B. A platinum element whose resistance is 100 Ω at 0 °C
Pt100 is a platinum RTD with R0 = 100 Ω at 0 °C; at 100 °C it is about 138.5 Ω (α = 0.00385 /°C). It is a resistance device, not a thermocouple, and has no emf sensitivity.
A Pt100 sensor (α = 0.00385 /°C, linear model) in a pasteuriser hot-water line reads 119.4 Ω. What is the temperature?
C. 50.4 °C
R = R0(1 + αT), so T = (R/R0 − 1)/α = (1.194 − 1)/0.00385 = 50.4 °C. 310.1 °C forgets to subtract 1; 19.4 °C takes the ohms change as degrees; 7.5 °C multiplies the 19.4 Ω change by α (with a factor-of-100 slip) instead of dividing.
Which thermocouple law allows a copper-wired voltmeter to be inserted into a thermocouple circuit without affecting the reading, provided both new junctions are at the same temperature?
B. The law of intermediate metals
The law of intermediate metals: a third metal inserted with both its junctions at the same temperature adds no net emf. The law of intermediate temperatures allows emfs over adjoining temperature intervals to be added; the homogeneous-circuit law says a single uniform wire produces no emf whatever its temperature gradient.
A 120 Ω foil strain gauge with gauge factor 2.0 is bonded to a plough beam that is strained to 500 µε. What is the change in its resistance?
A. 0.12 Ω
ΔR = R·GF·ε = 120 × 2.0 × 500×10⁻⁶ = 0.12 Ω. 1.20 Ω uses 5000 µε; 0.06 Ω forgets the gauge factor. Changes this small are why a Wheatstone bridge is needed.
What is the main advantage of the 'live zero' of 4 mA in a 4–20 mA signal from a field level transmitter?
C. A reading of 0 mA shows a broken wire or failed transmitter, not a zero level
With 4 mA as zero, any current well below 4 mA indicates a fault, and 4 mA can also power a two-wire transmitter. Immunity to cable resistance comes from current signalling in general, not from the live zero.
What is the size of one least significant bit (LSB) for a 12-bit ADC with a 0–5 V input range?
C. 1.22 mV
LSB = FS/2ⁿ = 5/4096 = 1.22 mV. 4.88 mV is the 10-bit value; 417 mV divides by the number of bits instead of 2ⁿ; 2.44 mV assumes a 10 V range.
Low-power wide-area network (LPWAN) radios are chosen for many farm sensors. What do they trade away to gain multi-kilometre range on battery power?
D. Data rate: they send only small packets, infrequently
LPWAN achieves long range at low power by using very low data rates and small payloads, often with duty-cycle limits. That suits a soil-moisture reading every 15 minutes, not video. Encryption is supported, and the radio does not change sensor accuracy.
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