A data logger is preferred to a spot reading when the quantity
Answer: C
A single reading of a fluctuating load is worth very little, and a week of logging reveals the night-time base load, the shift pattern and the peaks. Accuracy is a property of the instrument rather than of the logging.
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A spot measurement of a varying load can mislead an audit because it may catch the load
Answer: D
A compressor measured while unloaded, or a furnace measured between charges, gives a figure that understates the annual consumption badly. Logging over a representative period, or at least several spot readings, is what protects the estimate.
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An intrusive measurement is avoided in an audit where possible because it
Answer: A
A plant manager will rarely stop production to let a meter be fitted, so the audit must work with clamp-on and non-contact instruments. Intrusive methods are often the more accurate, which is the compromise being accepted.
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Calibration traceable to a national standard matters for an audit instrument because
Answer: B
Correct answer: the savings claimed rest on the readings being defensible
An audit produces figures that justify capital spending, support a performance contract or are reported for compliance, and those figures are only as good as the instruments behind them. Traceable calibration is what allows a reading to be defended when it is challenged, along with a stated uncertainty. It has nothing to do with the instrument’s range or with any blanket legal requirement.
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An instrument's accuracy specified as a percentage of full scale means the error at a tenth of full scale is
Answer: C
One per cent of full scale on a reading of a tenth of full scale is ten per cent of that reading, which is why the range must be chosen so the reading sits high in it. A specification as a percentage of reading behaves quite differently.
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An instrument used on a 415 V distribution board must carry
Answer: D
The category expresses the transient the instrument and its leads can survive at that point in the installation, and one rated for a socket outlet is not safe at a main switchboard. It is a safety requirement rather than an accuracy one.
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Match the instrument with what it establishes.
1. Flue gas analyser 2. Lux meter 3. Ultrasonic leak detector
P. Compressed air escaping from a main Q. Illumination at the working plane R. Excess air in the combustion
Answer: A
Correct answer: 1-R, 2-Q, 3-P
Three instruments for three quite different quantities. The flue gas analyser measures oxygen and carbon dioxide in the stack and reports the excess air, which is the first thing a boiler audit wants. The lux meter measures illumination at the working plane, which is what a lighting scheme must deliver. And the ultrasonic detector hears the high-frequency hiss of compressed air escaping through a leak, which is inaudible above the plant noise.
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Match the flow instrument with its characteristic.
1. Orifice plate 2. Clamp-on ultrasonic 3. Vane anemometer
P. Non-intrusive, defeated by aeration Q. Air velocity at a grille R. Permanent, with a lasting pressure loss
Answer: B
Each suits a different medium and a different constraint, and the pressure loss of the first is itself an energy cost the audit should note. Choosing the wrong one either interrupts the process or produces a figure that cannot be trusted.
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Consider the following statements about audit instruments.
1. An averaging clamp meter reads low on a distorted current 2. An infrared thermometer needs the emissivity to be set 3. A spot reading is adequate for a varying load
Answer: C
Correct answer: 1 and 2 only are correct
Statements 1 and 2 are correct: an averaging meter is calibrated for a sine wave and under-reads a distorted current, so a true RMS instrument is needed wherever drives or electronic loads are present; and an infrared thermometer computes temperature from radiance, so the emissivity setting must match the surface. Statement 3 is wrong - a varying load needs logging over a representative period, since a spot reading captures one moment of it.
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Which of the following would NOT be established with a power analyser?
Answer: D
Correct answer: the illumination level in the workshop
Illumination is measured with a lux meter, which responds to light rather than to voltage and current. Harmonic distortion, power factor and logged energy are all standard power analyser outputs, and it is precisely that combination in one instrument that makes it the workhorse of an electrical audit.
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