NCEES PE Agricultural and Biological Engineering · USA · NCEES (ASABE is the content partner)
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
NCEES PE Agricultural and Biological Engineering
Applying sensors and data acquisition in system problems: flow measurement for irrigation and processing, environmental monitoring of animal and plant facilities, control strategies for dryers and ventilation.
How our questions for NCEES PE Agricultural and Biological Engineering spread across the units of Instrumentation, Sensors & Process Control. Difficulty: 6 easy, 22 medium, 17 hard.
| IoT sensor networks | 9 | |
| Moisture measurement | 6 | |
| Control modes: on-off, P, PI and PID | 6 | |
| Pressure, flow and level measurement | 5 | |
| Data acquisition and data loggers | 5 | |
| Programmable logic controllers | 4 | |
| Force, torque and strain: strain gauges and load cells | 3 | |
| Signal conditioning | 3 | |
| The generalised measurement system | 2 | |
| Static and dynamic characteristics of instruments | 1 | |
| Temperature transducers | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
PTO power is calculated as P = 2πNT/60. Torque T is measured to ±1.0% and shaft speed N to ±0.5%, independently. What is the most probable relative uncertainty in P?
D. ±1.12%
For a product of powers, relative uncertainties combine by root sum of squares (each exponent is 1): √(1.0² + 0.5²) = 1.12%. ±1.50% is the worst-case arithmetic sum; ±0.75% is the average; ±0.50% keeps only the smaller term.
Dryer plenum air warms steadily at 2 °C per minute. The air-temperature sensor is first-order with a time constant of 30 s. Once the ramp is established, how far does the reading lag behind the true temperature?
B. 1.0 °C
For a ramp, a first-order sensor lags by rate × τ = (2 °C/60 s) × 30 s = 1.0 °C. 60 °C multiplies 2 by 30 without converting minutes to seconds; 2.0 °C would correspond to a 60 s time constant; 0.033 °C is the rate per second, not the lag.
An infrared thermometer set to emissivity 0.95 is pointed at the bare polished stainless-steel outer wall of a hot-air duct and reads far below a contact thermocouple. What is the most likely cause?
A. The polished metal has low emissivity, so it emits less than the 0.95 setting assumes
Shiny metals have low emissivity (often well below 0.3), so with the instrument set to 0.95 it underestimates temperature, and it also picks up reflected radiation from the surroundings. The fix is high-emissivity tape or paint on the spot, or a contact measurement. Infrared does not see through steel.
A turbine meter on a fertigation line has a K-factor of 50 pulses per litre. A counter records 1500 pulses in 60 s. What is the flow rate?
A. 30 L/min
Volume = 1500/50 = 30 L in 60 s, i.e. 30 L/min (0.5 L/s). 75 L/min multiplies 1500 by 50 and divides by 1000; 3000 L/min multiplies the K-factor by the 60 s count period; 1.25 L/min takes the 75 L/min slip and divides it by 60 again.
A TDR probe has 0.20 m rods. The two-way travel time of the pulse along the rods is 5.33 ns (c = 3×10⁸ m/s). Using the Topp equation, what is the volumetric water content?
B. 0.291 m³/m³
Ka = (c·t/2L)² = (3×10⁸ × 5.33×10⁻⁹ / 0.40)² = (3.998)² = 16.0. Topp: θv = −0.053 + 0.0292(16) − 5.5×10⁻⁴(256) + 4.3×10⁻⁶(4096) = 0.291. 0.467 keeps only the linear term; 0.689 treats 5.33 ns as a one-way time (Ka = 64); 0.055 forgets to square, using Ka = 4.
In a grain plant, the bucket elevator motor trips on overload while the intake conveyor and the bin-fill conveyor are running. What should the interlock logic do?
B. Stop the intake conveyor feeding the elevator at once, and let the bin-fill conveyor run on to empty
Every machine feeding a stopped machine must stop, or grain piles up and chokes the elevator. Machines downstream can run on to empty. Automatic restart after an overload trip is unsafe; the cause must be found first.
In an ultimate-cycle test on a dryer burner loop, sustained oscillation occurs at Ku = 8 with period Pu = 120 s. What are the Ziegler–Nichols PID settings?
D. Kp = 4.8, Ti = 60 s, Td = 15 s
Ziegler–Nichols PID: Kp = 0.6Ku = 4.8, Ti = Pu/2 = 60 s, Td = Pu/8 = 15 s. Kp = 3.6 with Ti = 100 s is the PI rule; 0.5Ku is the P-only rule. These settings give quarter-amplitude decay and are usually softened in practice.
What is the main trade-off of a mesh topology compared with a star topology in a field sensor network?
B. It extends coverage around obstacles, but relaying nodes use more energy and add latency
In a mesh, nodes relay each other's packets, so the network can reach around obstacles and beyond one hop, at the cost of extra listening and transmitting energy on relaying nodes, and more complex routing. A star needs every node in direct range of the gateway.
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.
An automated irrigation system starts a pump whenever one soil-moisture node reports a value below threshold. One night the node's probe is pulled partly out of the soil by a rodent and the pump runs for 10 hours. What design change best prevents this?
D. Cross-check against other sensors or a water-balance model, flag sudden steps, and cap run time
No sensor is immune to physical failure. Automated decisions should check plausibility (sudden steps, out-of-range values), agree with redundant sensors or a model, and have hard limits such as maximum run time and flow-meter confirmation. More frequent faulty readings do not help.
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